ADDITIVE MANUFACTURING PROCESSES AND ADDITIVELY MANUFACTURED PRODUCTS

[0001] The present application is a non-provisional of, and claims benefit or priority from each of U.S. Provisional Patent Application No. 62/806,901, filed Feb. 17, 2019, and U.S. Provisional Patent Application No. 62/717,444, filed Aug. 10, 2019, each of which is expressly incorporated herein by reference in its entirety.

[0002] The present invention relates to the field of additive manufacturing, and more particularly to additive manufacturing by controlled focused energy (e.g., laser or electron-beam) melting of particles, on a dissimilar substrate, specifically glasses and ceramics.

[0003] Each reference cited herein is expressly incorporated by reference in its entirety, for all purposes.

[0004] Additive manufacturing is well known. See the following U.S. patents and published patent applications: U.S. Pat. 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20170151719; 20170154713; 20170155309; 20170157850; 20170159447; 20170164700; 20170165532; 20170165751; 20170165752; 20170165753; 20170165754; 20170165781; 20170165790; 20170165791; 20170165792; 20170165916; 20170167000; 20170167270; 20170167274; 20170173628; 20170173681; 20170173683; 20170173688; 20170173691; 20170173692; 20170173693; 20170173694; 20170173695; 20170173696; 20170173697; 20170173735; 20170173736; 20170173737; 20170173747; 20170173868; 20170173872; 20170173874; 20170173877; 20170173878; 20170173879; 20170173883; 20170173892; 20170175756; 20170181291; 20170182556; 20170182558; 20170182560; 20170182594; 20170182596; 20170182598; 20170183497; 20170183870; 20170186143; 20170189553; 20170189961; 20170189962; 20170189963; 20170189964; 20170189965; 20170191177; 20170197246; 20170197278; 20170197330; 20170197359; 20170203355; 20170203363; 20170203364; 20170203365; 20170203387; 20170203391; 20170203406; 20170203408; 20170203517; 20170209908; 20170209923; 20170209929; 20170209931; 20170209954; 20170209958; 20170209963; 20170210070; 20170210144; 20170211331; 20170216916; 20170216921; 20170216966; 20170217093; 20170217095; 20170217105; 20170217181; 20170218228; 20170219855; 20170220031; 20170225227; 20170225228; 20170225229; 20170225393; 20170225394; 20170225398; 20170226362; 20170231783; 20170232511; 20170232513; 20170232514; 20170232515; 20170232518; 20170232519; 20170232549; 20170232552; 20170232557; 20170232637; 20170232674; 20170233574; 20170234138; 20170239718; 20170239719; 20170239720; 20170239721; 20170239722; 20170239723; 20170239724; 20170239725; 20170239752; 20170239887; 20170239891; 20170239892; 20170241830; 20170242424; 20170246682; 20170246689; 20170246709; 20170246804; 20170247785; 20170248319; 20170249440; 20170252787; 20170252806; 20170252812; 20170252813; 20170252814; 20170252815; 20170252816; 20170252817; 20170252818; 20170252819; 20170252820; 20170252846; 20170252851; 20170252854; 20170252860; 20170252967; 20170252978; 20170259502; 20170260865; 20170266759; 20170266879; 20170271837; 20170274454; 20170274456; 20170276023; 20170282246; 20170282247; 20170282296; 20170282297; 20170282455; 20170284676; 20170291077; 20170291260; 20170291261; 20170291263; 20170291362; 20170292174; 20170292195; 20170294288; 20170294291; 20170297097; 20170297098; 20170297099; 20170297100; 20170297101; 20170297102; 20170297103; 20170297104; 20170297106; 20170297108; 20170297109; 20170297111; 20170297267; 20170297275; 20170297674; 20170299181; 20170299973; 20170304894; 20170304895; 20170304896; 20170304897; 20170304900; 20170304944; 20170304945; 20170304946; 20170304947; 20170306221; 20170306447; 20170306448; 20170306449; 20170306450; 20170306457; 20170306458; 20170306459; 20170306460; 20170306766; 20170307859; 20170312821; 20170312822; 20170312826; 20170312857; 20170312858; 20170312984; 20170312985; 20170314109; 20170314114; 20170315538; 20170320162; 20170320168; 20170320264; 20170320277; 20170322487; 20170323627; 20170326668; 20170326681; 20170326690; 20170326788; 20170326797; 20170326805; 20170326816; 20170332733; 20170333994; 20170333995; 20170334023; 20170334024; 20170334133; 20170334136; 20170334725; 20170335436; 20170338392; 20170341141; 20170341142; 20170341175; 20170341182; 20170341183; 20170342303; 20170342535; 20170348458; 20170348792; 20170348906; 20170348909; 20170350259; 20170354805; 20170354806; 20170355135; 20170355138; 20170355146; 20170355147; 20170356068; 20170360534; 20170361405; 20170368603; 20170368640; 20170368647; 20170368740; 20170368816; 20180000501; 20180000502; 20180000503; 20180000571; 20180001423; 20180001424; 20180001547; 20180001553; 20180001556; 20180001557; 20180001567; 20180009007; 20180009054; 20180009064; 20180009134; 20180010001; 20180010221; 20180010237; 20180014844; 20180015564; 20180015565; 20180015566; 20180021473; 20180021877; 20180021878; 20180022022; 20180022065; 20180027615; 20180027616; 20180029124; 20180029125; 20180029241; 20180029294; 20180029295; 20180029306; 20180031028; 20180036939; 20180036945; 20180036953; 20180038167; 20180042718; 20180043455; 20180043467; 20180044523; 20180050390; 20180050423; 20180050490; 20180050493; 20180050495; 20180052087; 20180055641; 20180056389; 20180056390; 20180056391; 20180056392; 20180056396; 20180056446; 20180057142; 20180061279; 20180065144; 20180065178; 20180065181; 20180065182; 20180065186; 20180065208; 20180065209; 20180065295; 20180065298; 20180065300; 20180065304; 20180065305; 20180065306; 20180065307; 20180065308; 20180065309; 20180065316; 20180065317; 20180065318; 20180065320; 20180065322; 20180066358; 20180066603; 20180067464; 20180071819; 20180071821; 20180071825; 20180071949; 20180071986; 20180071988; 20180071989; 20180072040; 20180072630; 20180078936; 20180079003; 20180079029; 20180079033; 20180079034; 20180079125; 20180085605; 20180085826; 20180085856; 20180086004; 20180087157; 20180088462; 20180089824; 20180093325; 20180093347; 20180093418; 20180093419; 20180094953; 20180095450; 20180096175; 20180098919; 20180099331; 20180104770; 20180105903; 20180111191; 20180111193; 20180111194; 20180111195; 20180111196; 20180111197; 20180111198; 20180111219; 20180111317; 20180111318; 20180111319; 20180111334; 20180113445; 20180115072; 20180116762; 20180117674; 20180117675; 20180117713; 20180117845; 20180122541; 20180124341; 20180125365; 20180126460; 20180126461; 20180126462; 20180126487; 20180126637; 20180126638; 20180126639; 20180126640; 20180126641; 20180126642; 20180126648; 20180126649; 20180126650; 20180126655; 20180126666; 20180126720; 20180127317; 20180128803; 20180133583; 20180133801; 20180133804; 20180133839; 20180133840; 20180133956; 20180133958; 20180134027; 20180136458; 20180141119; 20180141123; 20180141126; 20180141127; 20180141159; 20180141160; 20180141162; 20180141174; 20180141235; 20180141274; 20180141305; 20180143147; 20180144934; 20180147627; 20180147628; 20180147653; 20180147654; 20180147655; 20180147669; 20180147779; 20180148378; 20180148379; 20180148380; 20180148585; 20180149039; 20180151048; 20180153205; 20180154437; 20180154438; 20180154439; 20180154440; 20180154441; 20180154442; 20180154443; 20180154444; 20180154484; 20180154574; 20180154580; 20180154591; 20180154657; 20180159016; 20180161873; 20180161874; 20180161875; 20180161932; 20180161934; 20180161935; 20180161954; 20180162013; 20180162044; 20180162047; 20180162048; 20180162053; 20180163311; 20180166251; 20180166665; 20180168254; 20180168294; 20180169351; 20180169756; 20180169784; 20180169950; 20180169951; 20180169952; 20180169960; 20180169970; 20180170107; 20180172369; 20180178284; 20180178285; 20180178286; 20180178287; 20180178288; 20180178325; 20180178326; 20180178413; 20180178491; 20180179332; 20180179956; 20180180803; 20180180812; 20180180813; 20180180874; 20180180896; 20180185098; 20180185893; 20180185921; 20180185961; 20180185965; 20180186067; 20180186078; 20180186080; 20180186081; 20180186082; 20180187569; 20180193916; 20180193923; 20180193953; 20180193954; 20180193955; 20180194080; 20180195186; 20180195684; 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20180272610; 20180272652; 20180273707; 20180281236; 20180281237; 20180281282; 20180281283; 20180281284; 20180281294; 20180289493; 20180290212; 20180290373; 20180296343; 20180297113; 20180297114; 20180297117; 20180297272; 20180297296; 20180303491; 20180303616; 20180304353; 20180304359; 20180304360; 20180304361; 20180304363; 20180304364; 20180304365; 20180304369; 20180304370; 20180304537; 20180304540; 20180305266; 20180307209; 20180309202; 20180311731; 20180311735; 20180311738; 20180318657; 20180318922; 20180318925; 20180318928; 20180318932; 20180318933; 20180319108; 20180319150; 20180320006; 20180323514; 20180326488; 20180326663; 20180326664; 20180326665; 20180326668; 20180333911; 20180333912; 20180333913; 20180337110; 20180338196; 20180345367; 20180345382; 20180345405; 20180345575; 20180345576; 20180354304; 20180354860; 20180355199; 20180360609; 20180361510; 20180361660; 20180361661; 20180361666; 20180361674; 20180369918; 20180370114; 20180370120; 20180370125; 20180370147; 20180370846; 20180370860; 20180371244; 20180374262; 20190000166; 20190001412; 20190001553; 20190001563; 20190001564; 20190001570; 20190001576; 20190002353; 20190009472; 20190010270; 20190017185; 20190020105; 20190022427; 20190022428; 20190022725; 20190022926; 20190026499; 20190030601; 20190030602; 20190030605; 20190030809; 20190030810; 20190030811; 20190031908; 20190031911; 20190033719; 20190033737; 20190039182; 20190039294; 20190039367; 20190047047; 20190047212; 20190047214; and 20190047277; and more generally CPC classes B33Y, B23K and B22F.

[0005] The current paradigm is to use a focused energy source (e.g., laser or electron beam) to fuse metal powders into a solid part by building on a baseplate that is identical or very similar to the build metal, to facilitate wetting. Capabilities offered by selective laser melting (SLM) enable industries to fabricate complex parts faster and cheaper by eliminating traditional forging, machining, and welding techniques. For instance, heat pipes have been directly metal printed via SLM with the wick structure made out of a printed lattice structure that enables low resistance fluid flow, while also producing the capillary driving force to draw coolant to the evaporator.[1, 2] A flat-plate oscillating heat pipe, that drives liquid coolant via temperature driven pressure variations has also been additively manufactured.[3] Performance enhancements have also been demonstrated for novel metal printed heat sinks and heat exchangers with lattice-architectures that are too complex to conventionally manufacture.[4, 5]

[0006] A prior additive manufacturing process does permit bonding of stainless steel substrates to Zr-metal glasses via laser welded V/Ti/Zr intermediate foil layers in a process called laser-foil-printing,[6] and laser welding dissimilar metals, like stainless steel and Ti via foil interlayers. [7, 8]

[0007] A prior technology permits low-temperature bonding of metal alloys onto semiconductor and ceramic substrates using active brazes. Elements such as Ti, Zr, V, Nb, Hf, Ta, Mo, Cr, and W can form intermetallic compounds (like silicides on Si and SiC, and carbides on graphite) or amorphisized mixtures of the substrate and reactive metal elements on the surface of many dissimilar substrates.[9-26] However the timescale of this bonding in these typical processes are more than three orders-of-magnitude longer than typical additive manufacturing processes energy source exposures in various additive manufacturing processes (powder bed fusion, directed energy deposition).[9, 19, 27, 28]

[0008] However, the art does not provide means to directly integrate these novel additively manufactured devices directly onto electronic devices.

[0009] The removal of heat from electronic circuits is important for reliability of electronic devices. The current electronic packaging paradigm has a microprocessor packaged with a bottom thermal interface material, a lid, and a top thermal interface material, and finally a heat removal device[29]. One embodiment of the technique developed herein can enable direct manufacture of heat removal devices on electronic devices, by removing the temperature drops due to thermal interface materials. Computational energy of integrated circuits versus temperature can be predicted via the changing power consumption with temperature[30, 31]. Furthermore, a leading cause of device failure is interconnects that break because of thermal cycling and electromigration. These interconnects are heated by the microprocessor, and their mean-time-to-failure is an exponential relation with temperature (Black's Law)[32]. A significant amount of e-waste can be reduced per year as many electronic device failures are thermally exacerbated, so the benefit of directly manufacturing heat sinks according to that embodiment is great.

[0010] Good wetting, as characterized by low contact angles, is an indication of strong mechanical bonding. Lower contact angles occur when more energetically favored bonding occurs between, for example, a liquid metal and a semiconductor, implying a stronger bond between the two surfaces. This wetting of dissimilar materials occurs via diffusion and dissolution of the substrate into the molten metal, and/or the metal into the substrate [9]. For example, intermetallic compounds may form. For reactive systems, wetting is limited by the diffusion of reactive elements and local reaction kinetics [10]. Many metals that melt at low temperatures do not wet silicon well, because they do not form silicides (e.g., Sn and Ag) [11]. While elements like Ti can amorphously bond to silicon at lower temperatures [12, 13], a stronger silicide bonds can be achieved above 550° C. [14]. Similar trends also exist for wetting of SiC, graphite and diamond, for instance.

[0011] An intermetallic (also called an intermetallic compound, intermetallic alloy, ordered intermetallic alloy, and a long-range-ordered alloy) is a type of metallic alloy that forms a solid-state compound exhibiting defined stoichiometry and ordered crystal structure. Intermetallic compounds may be defined as solid phases containing two or more metallic elements, with optionally one or more non-metallic elements, whose crystal structure differs from that of the other constituents. Under this definition, Electron (or Hume-Rothery, see en.wikipedia.org/wiki/Hume-Rothery_rules, www.phase-trans.msm.cam.ac.uk/2004/titanium/hume.rothery.html; Massalski, Tadeusz Bronislav, and Uichirō Mizutani. “Electronic structure of Hume-Rothery phases.” Progress in Materials Science 22, no. 3-4 (1978): 151-262; Mizutani, Uichiro. “The Hume-Rothery rules for structurally complex alloy phases.” In Surface Properties And Engineering Of Complex Intermetallics, pp. 323-399. 2010; Hume-Rothery, William. “The structure of metals and alloys.” Indian Journal of Physics 11 (1969): 74-74; Paxton, A. T., M. Methfessel, and D. G. Pettifor. “A bandstructure view of the Hume-Rothery electron phases.” Proceedings of the Royal Society of London. Series A: Mathematical, Physical and Engineering Sciences 453, no. 1962 (1997): 1493-1514.) compounds; Size packing phases. e.g., Laves phases (Stein, Frank, Martin Palm, and Gerhard Sauthoff. “Structure and stability of Laves phases. Part I. Critical assessment of factors controlling Laves phase stability.” Intermetallics 12, no. 7-9 (2004): 713-720; Stein, Frank, Martin Palm, and Gerhard Sauthoff. “Structure and stability of Laves phases part II—structure type variations in binary and ternary systems.” Intermetallics 13, no. 10 (2005): 1056-1074; Johnston, Roy L., and Roald Hoffmann. “Structure-Bonding Relationships in the Laves Phases.” Zeitschrift für anorganische und allgemeine Chemie 616, no. 10 (1992): 105-120.), Frank-Kasper phases (en.wikipedia.org/wiki/Frank-Kasper_phases; Joubert, J. M.; Crivello, J. C. (2012). “Non-Stoichiometry and Calphad Modeling of Frank-Kasper Phases”. Applied Sciences. 2 (4): 669. doi:10.3390/app2030669; Berne, C.; Sluiter, M.; Pasturel, A. (2002). “Theoretical approach of phase selection in refractory metals and alloys”. Journal of Alloys and Compounds. 334: 27. doi:10.1016/S0925-8388(01)01773-X.) and Nowotny phases (en.wikipedia.org/wiki/Nowotny_phase, Lu, Guoxin; Lee, Stephen; Lin, Jianhua; You, Liping; Sun, Junliang; Schmidt, Joshua Teal (2002). “RuGavSnw Nowotny Chimney Ladder Phases and the 14-Electron Rule”. Journal of Solid State Chemistry. 164 (2): 210-219. doi:10.1006/jssc.2001.9462; King, R. Bruce (2007). “The Relationship between the Nowotny Chimney Ladder”. Revista de Chimie. 58 (5): 439-441; Fredrickson, Daniel C.; Lee, Stephen; Hoffmann, Roald; Lin, Jianhua (2004). “The Nowotny Chimney Ladder Phases: Following the Pseudo Clue Toward an Explanation of the 14 Electron Rule”. Inorganic Chemistry. 43 (20): 6151-6158. doi:10.1021/ic049427n. PMID 15446859; Jeitschko, Pearson, W. B. (1970). “Phases with Nowotny chimney-ladder structures considered as ‘electron’ phases”. Acta Crystallographica Section B. 26 (7): 1044-1046. doi:10.1107/S0567740870003564; Fredrickson, Daniel C.; Lee, Stephen; Hoffmann, Roald (2004). “The Nowotny Chimney Ladder Phases: Whence the 14 Electron Rule?”. Inorganic Chemistry. 43 (20): 6159-6167. doi:10.1021/ic049897h. PMID 15446860.); and Zintl phases (en.wikipedia.org/wiki/Zintl_phase; S. M. Kauzlarich, Encyclopedia of Inorganic chemistry, 1994, John Wiley & Sons, ISBN 0-471-93620-0; Fässler, Thomas F. (2011). “Zintl Phases: Principles and Recent Developments”. 139. doi:10.1007/978-3-642-21150-8. ISSN 0081-5993; Sevov, S. C., Zintl Phases in Intermetallic Compounds, Principles and Practice: Progress, Westbrook, J. H.; Freisher, R. L.: Eds.; John Wiley & Sons. Ltd., Chichester, England, 2002, pp. 113-132 (Slavi Chapter); Cotton, F. Albert; Wilkinson, Geoffrey; Murillo, Carlos A.; Bochmann, Manfred (1999), Advanced Inorganic Chemistry (6th ed.), New York: Wiley-Interscience, ISBN 0-471-19957-5) are encompassed. The definition of a metal is taken to include the so-called post-transition metals, i.e. aluminum, gallium, indium, thallium, tin and lead, some, if not all, of the metalloids, e.g., silicon, germanium, arsenic, antimony and tellurium, and homogeneous and heterogeneous solid solutions of metals, but interstitial compounds (such as carbides and nitrides), are excluded under this definition. However, interstitial intermetallic compounds are included, as are alloys of semimetal compounds with a metal. For purposes hereof, the phrase “intermetallic” compounds also encompasses certain intermetallic-like compounds, i.e., crystalline metal compounds other than halides or oxides, and including such semimetals, carbides, nitrides, borides, sulfides, selenides, arsenides, and phosphides, and can be stoichiometric, and share similar properties to the intermetallic compounds defined above, including the facilitation of layer adhesion. Thus, compounds such as cementite, Fe₃C, is included. See, en.wikipedia.org/wiki/Intermetallic. The interfacial layer may have amorphous characteristics, e.g., due to rapid cooling.

[0012] See also U.S. Patent and Patent Application Nos. U.S. Pat. Nos. 4,026,677; 4,034,454; 4,034,906; 4,065,302; 4,171,339; 4,173,614; 4,234,661; 4,241,135; 4,358,506; 4,380,574; 4,396,677; 4,459,062; 4,510,171; 4,518,468; 4,553,856; 4,640,816; 4,683,019; 4,699,310; 4,714,624; 4,725,509; 4,818,628; 4,861,751; 4,873,152; 4,880,614; 4,911,987; 4,916,022; 4,956,011; 4,985,313; 5,015,502; 5,034,274; 5,039,990; 5,047,386; 5,071,828; 5,087,515; 5,104,849; 5,132,278; 5,135,817; 5,154,425; 5,188,164; 5,204,302; 5,209,987; 5,224,969; 5,234,715; 5,247,986; 5,255,730; 5,262,202; 5,266,357; 5,270,296; 5,289,967; 5,326,525; 5,328,717; 5,338,598; 5,342,812; 5,350,637; 5,352,519; 5,362,523; 5,366,570; 5,378,500; 5,422,209; 5,429,843; 5,434,027; 5,458,480; 5,458,705; 5,476,725; 5,490,911; 5,498,298; 5,503,703; 5,516,725; 5,526,914; 5,538,674; 5,580,403; 5,620,791; 5,624,505; 5,648,177; 5,669,436; 5,683,825; 5,686,178; 5,694,184; 5,709,958; 5,741,376; 5,747,111; 5,761,787; 5,770,273; 5,834,070; 5,837,960; 5,865,909; 5,873,771; 5,880,692; 5,939,201; 5,939,224; 5,948,541; 5,964,020; 5,976,716; 5,989,728; 5,993,979; 6,001,461; 6,017,628; 6,019,878; 6,054,185; 6,077,615; 6,086,959; 6,096,436; 6,117,533; 6,129,996; 6,159,267; 6,163,961; 6,214,195; 6,232,037; 6,267,864; 6,277,169; 6,322,897; 6,355,338; 6,372,346; 6,513,433; 6,528,145; 6,531,704; 6,534,194; 6,537,689; 6,540,800; 6,541,695; 6,551,760; 6,558,841; 6,566,035; 6,589,311; 6,596,150; 6,607,844; 6,612,478; 6,613,697; 6,635,357; 6,663,982; 6,669,774; 6,669,989; 6,673,387; 6,676,728; 6,682,780; 6,689,186; 6,699,304; 6,713,519; 6,723,279; 6,730,410; 6,740,464; 6,749,101; 6,765,151; 6,779,951; 6,780,305; 6,797,313; 6,797,449; 6,800,400; 6,800,417; 6,806,478; 6,824,689; 6,828,507; 6,847,699; 6,858,374; 6,875,949; 6,893,732; 6,899,777; 6,909,173; 6,909,192; 6,913,184; 6,929,865; 6,939,505; 6,974,070; 6,974,501; 6,979,646; 6,989,200; 7,004,994; 7,005,191; 7,008,969; 7,011,760; 7,022,165; 7,052,241; 7,060,222; 7,076,959; 7,094,473; 7,097,938; 7,105,217; 7,122,279; 7,145,244; 7,157,188; 7,162,302; 7,169,478; 7,172,663; 7,174,637; 7,192,673; 7,195,842; 7,235,330; 7,241,416; 7,241,533; 7,259,032; 7,282,444; 7,285,337; 7,285,496; 7,287,960; 7,288,576; 7,299,749; 7,300,559; 7,309,548; 7,311,944; 7,318,983; 7,326,434; 7,338,741; 7,351,773; 7,354,471; 7,361,239; 7,381,517; 7,393,559; 7,410,728; 7,413,109; 7,416,835; 7,432,014; 7,451,906; 7,455,458; 7,459,233; 7,476,469; 7,560,138; 7,575,039; 7,597,769; 7,604,897; 7,608,178; 7,621,976; 7,622,424; 7,625,668; 7,626,665; 7,629,058; 7,642,468; 7,645,543; 7,666,233; 7,674,555; 7,722,731; 7,726,872; 7,736,542; 7,736,794; 7,745,050; 7,759,007; 7,771,547; 7,781,376; 7,782,433; 7,794,881; 7,820,332; 7,838,170; 7,858,205; 7,896,222; 7,939,126; 7,940,361; 7,976,985; 7,997,472; 8,007,178; 8,007,929; 8,017,263; 8,025,983; 8,025,984; 8,048,571; 8,063,489; 8,071,419; 8,079,141; 8,097,301; 8,097,303; 8,119,288; 8,119,314; 8,119,315; 8,137,525; 8,173,010; 8,173,269; 8,182,939; 8,182,943; 8,202,649; 8,216,439; 8,221,921; 8,236,452; 8,247,142; 8,273,194; 8,313,560; 8,319,350; 8,323,820; 8,334,075; 8,353,574; 8,354,136; 8,372,685; 8,377,999; 8,389,060; 8,389,147; 8,394,495; 8,410,016; 8,425,651; 8,428,671; 8,436,130; 8,440,498; 8,455,131; 8,465,847; 8,466,095; 8,487,439; 8,507,132; 8,512,808; 8,563,872; 8,591,997; 8,604,350; 8,617,640; 8,623,554; 8,629,564; 8,632,850; 8,636,194; 8,637,864; 8,652,686; 8,658,304; 8,673,050; 8,673,477; 8,692,127; 8,697,322; 8,723,176; 8,748,241; 8,759,473; 8,778,538; 8,789,626; 8,795,899; 8,796,683; 8,802,286; 8,810,035; 8,828,579; 8,840,831; 8,852,801; 8,853,867; 8,860,021; 8,882,442; 8,893,954; 8,901,558; 8,906,462; 8,906,469; 8,916,424; 8,921,473; 8,932,771; 8,946,704; 8,952,380; 8,956,478; 8,956,766; 8,956,912; 8,960,523; 8,962,188; 8,963,148; 8,969,867; 8,979,606; 8,986,880; 8,999,200; 9,005,821; 9,006,733; 9,011,620; 9,040,981; 9,045,335; 9,054,364; 9,070,729; 9,076,825; 9,078,294; 9,079,246; 9,083,054; 9,090,955; 9,093,383; 9,097,995; 9,101,978; 9,109,429; 9,113,571; 9,117,662; 9,127,515; 9,130,358; 9,136,568; 9,142,679; 9,153,436; 9,166,019; 9,166,061; 9,171,787; 9,176,571; 9,181,790; 9,184,160; 9,190,529; 9,190,666; 9,205,578; 9,209,480; 9,214,566; 9,218,966; 9,219,161; 9,227,243; 9,236,428; 9,236,606; 9,243,475; 9,252,283; 9,252,286; 9,263,259; 9,269,647; 9,281,517; 9,287,405; 9,287,573; 9,296,190; 9,318,484; 9,324,875; 9,330,909; 9,331,156; 9,331,251; 9,350,005; 9,354,029; 9,402,313; 9,414,513; 9,419,299; 9,428,826; 9,431,430; 9,437,744; 9,440,853; 9,466,725; 9,472,310; 9,472,656; 9,476,685; 9,482,105; 9,488,456; 9,496,375; 9,508,979; 9,530,895; 9,536,844; 9,545,017; 9,556,505; 9,559,213; 9,564,457; 9,564,589; 9,587,296; 9,593,924; 9,601,779; 9,608,124; 9,614,062; 9,614,100; 9,643,250; 9,643,279; 9,656,877; 9,660,265; 9,666,896; 9,682,425; 9,722,275; 9,728,648; 9,728,773; 9,731,377; 9,735,428; 9,742,001; 9,744,743; 9,765,271; 9,765,635; 9,780,348; 9,793,057; 9,812,467; 9,812,582; 9,818,715; 9,832,866; 9,833,838; 9,835,428; 9,852,904; 9,857,860; 9,859,114; 9,862,617; 9,871,059; 9,881,744; 9,899,136; 9,899,672; 9,903,037; 9,905,860; 9,911,874; 9,916,958; 9,919,472; 9,938,839; 9,943,927; 9,943,929; 9,947,964; 9,954,212; 9,960,122; 9,990,965; 9,991,221; 9,991,395; 9,997,545; 9,997,784; RE41584; RE43661; RE44817; RE44820; RE46275; 20010000889; 20010018159; 20010028990; 20010038029; 20020007751; 20020009626; 20020056401; 20020062858; 20020069592; 20020081447; 20020082171; 20020084527; 20020090821; 20020098381; 20020098776; 20020110698; 20020144838; 20020153253; 20020154741; 20020160308; 20020168051; 20020177003; 20020192494; 20020192564; 20020195676; 20030019326; 20030022094; 20030029910; 20030044593; 20030068575; 20030108795; 20030116503; 20030119920; 20030127051; 20030161750; 20030162127; 20030173720; 20030180571; 20030189082; 20040009402; 20040016912; 20040018432; 20040035910; 20040071882; 20040081895; 20040096742; 20040100164; 20040106060; 20040112478; 20040147620; 20040149806; 20040154488; 20040168637; 20040182835; 20040197650; 20040202883; 20040206267; 20040210289; 20040219295; 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20060274510; 20060276875; 20060280998; 20070000129; 20070002239; 20070010702; 20070054189; 20070061006; 20070065675; 20070068605; 20070072113; 20070093006; 20070099088; 20070104605; 20070111893; 20070122549; 20070122707; 20070122710; 20070128520; 20070128521; 20070140065; 20070141469; 20070152026; 20070158200; 20070160315; 20070178384; 20070187464; 20070227627; 20070251389; 20070298325; 20070298351; 20080015284; 20080032192; 20080041921; 20080057203; 20080057395; 20080057616; 20080075878; 20080075984; 20080152998; 20080156475; 20080175982; 20080188373; 20080241660; 20080241705; 20080280201; 20080299459; 20090000480; 20090046441; 20090110954; 20090114797; 20090117466; 20090123690; 20090136769; 20090155676; 20090178741; 20090214373; 20090214857; 20090235915; 20090269497; 20090269605; 20090288952; 20090291312; 20090291345; 20090297718; 20090311598; 20090317658; 20100013096; 20100015330; 20100029036; 20100062179; 20100078830; 20100089976; 20100089977; 20100102446; 20100112192; 20100133688; 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[0013] Glasses are class of ceramic that have short range order, but lack long-range order (i.e., amorphous) and are often made from oxides (e.g., silica, alumina, beryllia, ceria, zirconia). Performance, strength, rheology, chemical inertness, optical properties and cost make glasses attractive materials for broad range of applications [33]. Conventional silica glasses consist of Si bonded tetrahedrally to four oxygen atoms. If the SiO₂ melt is quenched it will harden as an amorphous solid. Amorphous networks of SiO₂ structure (short range order) results in glassy forms [34-36] such as Soda-lime-silica glass. Furthermore, various chemical and physical processes can be performed to modify glass properties. As an example, borosilicate glass exhibits high thermal shock and chemical resistance as a result of ion diffusion (boron) to silica. Borosilicate glass will phase separate into silica glass regions and small precipitates of boric glass [37]. Glasses can be made by melting or non-melting based techniques such as physical vapor deposition [36, 38], neutron irradiation of crystalline structures [36, 39] and sol-gel processing of solutions [36, 40].

[0014] If on the other hand, the melt is slowly cooled, a crystalline quartz structure with long range order results [41] Crystallinity of ceramics ranges from highly-oriented to complete amorphous structures or some combination.

[0015] As glasses, ceramics and metals are widely used in various industries, such as semiconductor, automotive, aerospace, defense, medical, environmental control, it is often beneficial and useful to build structures containing glass or ceramics and metals.

[0016] Bettger et al. demonstrated a method to chemically bond soda-lime glass to metal structures consisting of stainless steel alloy, a carbon steel, titanium, aluminum or copper [42]. In this technique, an oxide layer including iron oxide and chromium oxide with iron-to-chromium ratio in the range of 0.02 to 0.6 (atom ratio) is deposited on glass substrate. By heating the metal substrate and glass substrate within the range of 500° C. to 1000° C. and placing them in contact with the oxide layer a bond in between is formed. The duration of contact varies between 10 seconds to 10 minutes based on temperature and pressure (not specified). The interfacial strength of the bond between glass and metal substrate is not quantitively discussed.

[0017] In another work McMilan et al. demonstrated the process of bonding glass or ceramic to metal by depositing a uniform layer of glass powder by dipping into a melt or spraying the glass powder suspension onto the metal component [43]. The powder coated metal part is then exposed to a gas-flame in air or nitrogen or in a nitrogen-hydrogen mixture to fuse the powder glass. The metals in the technique should be sandblasted and pre-oxidized before the powder deposition. Ag, Cu and Au metals act as nucleating agent for glass crystallization in the controlled devitrification process and create the bonds to the metal. This devitrification refers to small domains that have crystallized and are no longer amorphous. In this process, the glass powder should be melted within the range of 1000° C. and capable of devitrification under heat treatment to create crystalline structure. Thermal expansion coefficient of post-devitrified glass and the metal should be close to prevent thermal stress and fracture during post heat treatment process. After the heat treatment of metal-glass component at 500° C. to 750° C., liquid state glass will be reflowed to a mold which then bonds to pre-glassed metal. The heat treatment stage varies from 5 minutes to 1 hour.

[0018] Bonding of bioglass to metal structures is beneficial for medical devices, like orthopedic and dental devices to improve biocompatibility. One of the greatest challenges in this application is that coefficient of thermal expansion of glasses and metals are dissimilar at melting and cooling process which poses large thermal stress and consequently cracks and failures are probable [44]. There are other limiting factors in conventional glass to metal bonding techniques such as flame spraying. Loss of compositional control during long flame exposure time, extremely high diffusion of metal ions into glass, limited choice of glass types that can match coefficient of thermal expansion of metal during heat treatment process are some of this limiting factors [42, 43]. In this bonding technique, similar to previous mentioned methods, the surface of the metal is roughened and oxidized and then heated up to desired glass transition temperature. Then the metal substrate is immersed in molten glass and after removal cooled down in a way to minimize thermomechanical stresses. The proposed metals are surgical stainless steel, carbon steel, cobalt-chrome alloys, titanium and titanium alloys, noble metals such as platinum, noble metal alloys such as platinum (% 90)-rhodium (% 10) and molybdenum-nickel-cobalt-chrome alloys [44].

[0019] The mentioned techniques so far consist of exposing both metal and glass components to high temperatures usually above glass transition temperatures in a furnace or a direct gas-flame. In another technique, it is possible to join ceramics such as lead-zirconite-titanate (PZT) to certain metal oxides (submicron TiO₂, material filled with silver particles) by compressing both substrates and exposing the interface to microwave beams. The localized microwave beams will heat up and soften the substrates at the interface and facilitate interdiffusion and reaction [45]. Glass frit can be used as intermediate layer to bond Si, SiO₂, Si₂N₄, Al, Ti, and Glass substrates [46-51]. However, thermal stress due to CTE mismatch is present.

[0020] Bonding of ceramics to metal has great importance in applications such as defense. There is the need to bond advanced ceramic elements to metallic components in missiles where the joints should be able to withstand temperatures ˜550° C. or even more for one minute and able to survive environmental thermal fluctuations from −40° C. to 200° C. [52]. In most cases of conventional ceramic-to-metal bonding techniques, thermal expansion coefficient of metals is higher than the ceramic. Furthermore, controlling compositional changes at the interface is rather challenging. Brazing is the favored solution for ceramic to metal bonding due to stable reactive diffusion. Silver-Copper composition containing 2% titanium is commercially available active filler material for conventional brazing [53-56]. High oxidation potential of titanium facilitates oxide redox reaction with ceramic which results in reactive wetting and chemical bond at the interface[52]. In the laser brazing process the temperature of the filler alloy is raised above melting point to cause wetting and reactive bonding to the material. Ceramic-to-metal bonds provided are bonding Ti to ZnS, Pyroceram to Kovar and Nb to Sapphire using Cusil™ and Lucanex 721®. As an example, ZnS is brazed to Ti by Ag—Cu—Ti alloy. The brazed bonds survived up to 12 cycles from 550° C. to liquid nitrogen temperatures and 50 cycles from 0° C. to 200° C. The laser processing was done under vacuum conditions in order to prevent oxidization reactions high reactive metals such as titanium.

[0021] Materials containing 90% alumina by weight or higher can bond to certain metals at specified temperatures [57]. Ceramics generally have poor wettability to metals. However, compositions of brazing alloy containing reactive elements such as Ti, Zr, V, Hf, Nb can bond to ceramic oxides (i.e. Al₂O₃) [58]. The alloy composition beside the reactive element can be chosen from Ag, Cu, Ni, Mn, In, Sn etc. [57]. Some of these elements are used to decrease the melting point of the braze alloy. Furthermore, by adding aluminum to the compound it is possible to further control the brazing alloy to alumina reaction.

[0022] The present technology provides methods and apparatus for bonding metals on to glass and ceramic substrates, including those composed of oxides (e.g., silica glass, quartz, borosilicate glass, alumina, beryllia, ceria, zirconia, lithium aluminum silicates, gallium oxide, indium tin oxide, indium zinc oxide), silicides (e.g., molybdenum disilicide), nitrides, and carbides (e.g., silicon carbide), carbon materials (e.g., diamond, pyrolytic graphite, carbon nanotubes, graphene, fullerenes), borides (e.g., tungsten borides), arsenides (e.g., gallium arsenide), sulfides (e.g., zinc sulfide) and also enables composites of metals and glasses or ceramics for various applications. Applications may include removable support layers, composite structures, connections to opto-electronics, pollution control devices, thermal devices to cool electronics.

[0023] This technology invention builds on the literature of low-temperature bonding of metal alloys onto glass and ceramic substrates using brazes, and seeks to overcome the aforementioned timescale limitations.

[0024] The present technology provides laser or electron-beam additive manufacturing of metal structures on ceramic and glass substrates.

[0025] The current paradigm is to use a focused energy source (e.g., laser or electron beam) to fuse metal powders into a solid part by building on a baseplate that is identical or very similar to the build metal to facilitate wetting. This is to create the strongest bonding to the build plate and minimize coefficient of thermal expansion mismatches.

[0026] One benefit of building on ceramic or glass is to enable direct manufacture of heat removal devices and/or electrical connections on opto-electronic substrates, integration of conventional composite materials into metal additive, heterogeneous integration of dissimilar materials, and for easy parting of the desired part from the support structure and/or the buildplate.

[0027] In one embodiment, a brazing alloy powder with homogeneous composition is employed. In another embodiment, the bonding metals are not homogeneous, i.e., are heterogeneous. The inhomogeneous brazing powder can have varying composition of the constituents, including separating each element into separate powders. In the inhomogeneous case, the powder sizes can be varied so that the largest phase has larger average diameter powder, while the lower concentration has smaller diameter to more evenly distribute around the bulk phase, for lower diffusional resistance. In some cases, the brazing powder may be deposited in layers, forming isotropic structures or regional differences. In certain embodiments, a metallization on the substrate can facilitate bonding.

[0028] In one embodiment, the bonding metal has an overall composition of about 1 to 10 wt % of an “active” brazing element plus the composition of solder for the balance of the composition. The “active” elements may include Ti, Zr, V, Nb, Hf, Ta, Mo, Cr, and W, which are suitable candidates for bonding of metals to various materials such as ceramics and glasses, including those composed of oxides (e.g., silica glass, quartz, borosilicate glass, alumina, beryllia, ceria, zirconia, lithium aluminum silicates, gallium oxide, indium tin oxide, indium zinc oxide), silicides (e.g., molybdenum disilicide), nitrides, and carbides, carbon materials (e.g., diamond, pyrolytic graphite, carbon nanotubes, graphene, fullerenes), borides (e.g., tungsten borides), arsenides (e.g., gallium arsenide), sulfides (e.g., zinc sulfide), as well as other metals [15] due to the interlayers they form that bond to those materials.

[0029] Embodiments may include using one or more of these active elements plus a solder. Embodiments may also include solders that mix elements such as Sn, Pb, Ag, Cu, Sb, Bi, In, Zn, Cd, Au, Ni, Si, Ge, Si, Al. Embodiments includes solders such as InSn (e.g., In₅₂Sn₄₈, In₆₀Sn₄₀, In₅₀Sn₅₀, In₄₂Sn₅₈), InCd (e.g., In₇₄Cd₂₆), BiPbInCdSn (e.g., Bi_44.7Pb_22.6In_19.1Cd_5.3Sn_8.3), InBiSn (e.g., In₅₁Bi_32.5Sn_16.5), InBiCd (e.g., In_61.7Bi_30.8Cd_7.5), BiPbSnIn (e.g., Bi₄₉Pb₁₈Sn₁₂In₂₁), BiPbSnCd (e.g., Bi₅₀Pb_26.7Sn_13.3Cd₁₀), BiSnIn (e.g., Bi₅₆Sn₃₀In₁₄), BiPbSn (e.g., Bi₅₂Pb₃₂Sn₁₆, Bi₅₀Pb_31.2Sn_18.8), BiPb (e.g., Bi₅₈Pb₄₂), SnPbBi (e.g., Sn₄₆Pb₄₆Bi₈), InSnPbCd (e.g., In₇₀Sn₁₅Pb_9.6Cd_5.4), SnPbIn (e.g., Sn₅₄Pb₂₆In₂₀, Sn_37.5Pb_37.5In₂₅, Sn₇₀Pb₁₈In₁₂), BiSnAg (e.g., Bi₅₇Sn₄₂Ag₁), BiSn (e.g., Bi₅₆Sn_42, Bi₅₈Sn₄₂), SnBiPb (e.g., Sn₄₈Bi₃₂Pb₂₀, Sn₄₃Pb₄₃Bi₁₄), CdSn (e.g., Cd₇₀Sn₃₀), InPbAg (e.g., In₈₀Pb₁₅Ag₅), InAg (e.g., In₉₇Ag_3, In₉₀Ag₁₀), SnPbCd (e.g., Sn_51.2Pb_30.6Cd_18.2), InPb (e.g., In₇₅Pb₂₅, In₇₀Pb_30, In₆₀Pb_40, In₅₀Pb₅₀, Pb₇₅In₂₅), In, PbSnZn (e.g., Pb₆₃Sn₃₄Zn₃), SnZnInBi (e.g., Sn_86.5Zn_5.5In_4.5Bi_3.5), SnInAg (e.g., Sn_77.2In₂₀Ag_2.8, Sn_86.9In₁₀Ag_3.1, Sn_91.8In_4.8Ag_3.4, Sn₈₈In_8.0Ag_3.5Bi_0.5), SnZnCd (e.g., Sn₄₀Zn₂₇Cd₃₃), SnPbZn (e.g., Sn₃₀Pb₅₀Zn₂₀), PbSnAg (e.g., Pb₅₄Sn₄₅Ag_1, Sn₆₂Pb₃₆Ag₂, Pb₈₀Sn₁₈Ag₂, Pb₉₆Sn₂Ag₂, Pb₈₈Sn₁₀Ag₂, Pb₉₂Sn_5.5Ag_2.5, Pb₉₀Sn₅Ag₅, Pb_93.5Sn₅Ag_1.5, Pb_95.5Sn₂Ag_2.5), SnZnIn (e.g., Sn_83.6Zn_7.6In_8.8), PbSn (e.g., Pb₉₀Sn_10, Pb₈₅Sn₁₅, Pb₈₀Sn₂₀, Sn₆₃Pb₃₇, Sn₇₀Pb₃₀, Sn₉₀Pb₁₀, Sn₆₃Pb₃₇P_0.0015-0.04, Sn₆₂Pb₃₇Cu₁, Sn_97.5Pb₁Ag_1.5,), SnZnBi (e.g., Sn₈₉Zn₈Bi₃), SnZn (e.g., Sn₉₁Zn_9, Sn₈₅Zn_15, Sn₆₀Zn_40, Zn₇₀sn_30, Zn₆₀Sn_40, Sn₅₀Zn₄₉Cu₁, Sn₉₀Zn₇Cu₃), SnBiAg (e.g., Sn_91.8Bi_4.8Ag_3.4), SnAgCu (e.g., Sn_96.5Ag_3.0Cu_0.5, Sn_95.5Ag_4.0Cu_0.5, Sn_95.8Ag_3.5Cu_0.7, Sn_95.6Ag_3.5Cu_0.9, Sn₉₉Cu_0.7Ag_0.3, Sn_96.2Ag_2.5Cu_0.8Sb_0.5, Sn_90.7Ag_3.6Cu_0.7Cr₅, Sn₉₅Ag_3.5Zn₁Cu_0.5, Sn_95.5Cu₄Ag_0.5, Sn₉₇Cu_2.75Ag_0.25), SnAu (e.g., Sn₉₀Au₁₀), SnAg (e.g., Sn_96.5Ag_3.5—Sn₉₃Ag₇), SnCu (e.g., Sn_99.3Cu_0.7, Sn₉₇Cu₃), SnPbZn (e.g., Sn₃₃Pb₄₀Zn₂₈), Sn, SnSb (e.g., Sn₉₅Sb₅—Sn₉₉Sb₁), SnAgSb (e.g., Sn₆₄Ag₂₅Sb₁₀), PbIn (e.g., Pb₈₁In₁₉, Pb₇₀In₃₀, Pb₇₅In₂₅, Pb₉₀In₅Ag₅, Pb_92.5In₅Ag_2.5, Pb_92.5In₅Au_2.5), CdZn (e.g., Cd_82.5Zn_17.5, Cd₇₀Zn₃₀, Cd₆₀Zn₄₀, Zn₉₀Cd₁₀, Zn₆₀Cd₄₀, Cd₇₈Zn₁₇Ag₅), Bi, AuSn (e.g., Au₈₀Sn₂₀), PbSbSn (e.g., Pb₈₀Sb₁₅Sn₅), PbAg (e.g., Pb_94.5Ag_5.5—Pb₉₆Ag₄, Pb₉₇Ag_1.5Sn₁, Pb_97.5Ag_2.5), CdAg (e.g., Cd₉₅Ag₅), AuSi (e.g., Au₉₈Si₂, Au_96.8Si_13.2), ZnAl (e.g., Zn₉₅Al₅), ZnSn (e.g., Zn₉₅Sn₅), Zn, AuIn (e.g., Au₈₂In₁₈), AuGe (e.g., Au_87.5Ge_12.5). Many of these possible bonding alloys are undesirable for due to health and environmental concerns (e.g., those containing Pb, Cd), and for economics due to cost (e.g., Au). However, these are not technologically excluded, and may be employed as appropriate in the application. Aluminum containing solders have advantage for bonding to Al₂O₃-based substrates.

[0030] In another embodiment, the bonding metal is a homogeneous or heterogeneous powder mixture of a brazing alloy. One specific embodiment of this invention uses the Sn₃Ag₄Ti composition as a heterogeneous or homogeneous composed powder. This alloy has good bonding strength with dissimilar metallic or non-metallic substrates at temperatures between 250° C. to 450° C. [15, 59, 17, 18]. Sn₃Ag₄Ti forms bonds with such materials as oxides (e.g., silica glass, quartz, borosilicate glass, alumina, beryllia, ceria, zirconia, lithium aluminum silicates, gallium oxide, indium tin oxide, indium zinc oxide), silicides (e.g., molybdenum disilicide), nitrides, and carbides, carbon materials (e.g., diamond, pyrolytic graphite, carbon nanotubes, graphene, fullerenes), borides (e.g., tungsten borides), arsenides (e.g., gallium arsenide), sulfides (e.g., zinc sulfide). To form a good bond, the braze or bonding alloy must minimize thermal stress from the solidification temperature to ambient, so the low melting point of the braze is beneficial. Furthermore, the low melting point increases the activity of the reactive metals by making it more available to react with the substrate. Brazing alloys generally have similar compositions to low-temperature solders, but also include an element that thermodynamically favors forming reactions with the substrate over other elements of the solder. Unlike a solid solution alloy with the different species randomly occupying lattice sites, intermetallics exist at specific stoichiometric ratios and each species has its own lattice sites. Intermetallics possess stiffer bonds than solid solution alloys because of their long range order, negative heats of formation and higher melting temperatures.

[0031] A different embodiment uses a homogeneous or heterogeneous powder mixture with a AgCuTi alloy. A different embodiment uses a Ag₂₁Cu₅X alloy where X═Ti, Ta, Zr, V, Hf, Cr, Mo, W, Nb.

[0032] In yet another embodiment, Cu or Cu alloy with an active element X═Ti, Ta, Zr, V, Hf, Cr, Mo, W, Nb at about 1-10 wt % is mixed as a homogeneous powder alloy, or as a heterogeneous mixed powder.

[0033] In yet another embodiment, Al or Al alloy, such as Al—Si alloys, is mixed with an active element X═Ti, Ta, Zr, V, Hf, Cr, Mo, W, Nb at about 1-10 wt % as a homogeneous powder alloy or as a heterogeneous mixed powder. These Al rich alloys are attractive for bonding to alumina rich substrates.

[0034] Certain embodiments can incorporate ceramic or semiconductor micro or nanoparticle inclusions. This can serve two purposes, to better match the coefficient of thermal expansion of the substrate, and to mechanically reinforce the interlayer material.

[0035] While the time to make a good bond in typical metal wetting is on the order of tens of minutes [9, 19, 27, 28], in additive manufacturing this nucleation and crystal growth of the intermetallic phase needs to occur in times of less than 100 μs per exposure, as the laser melting and solidification occur rapidly [60, 61]. Hence, achieving a good bond with powder bed-additive manufacturing poses unique challenges compared to conventional brazing that are overcome through aspects of this invention.

[0036] Several embodiments overcome this kinetic limitation. One such aspect is to repeatedly melt the same area to increase the overall time at elevated temperature, which increases time for bonding elements to diffuse to the interface and for metals to form bonding compounds (e.g., intermetallics, oxides, nitrides, carbides, silicides, borides, arsenides). This multiple exposure is beneficial for protecting the electronics and the substrate because each directed energy melting pulse is brief enough that the thermal penetration depth does not exceed the thickness of the typical silicon wafer. This directed energy pulse may be from a source like a laser or an electron beam. Less focusable energy sources, like a microwave or a hot solder iron tip that moves over the part, could also be used in alternative embodiments as energy sources. Moreover, momentary high temperature helps to overcome the energy barriers for diffusion and crystallization better than in a longer duration, lower heating temperature found in conventional brazing, due to diffusivity and nucleation rate being an exponential function of temperature. This elevated temperature overcomes barriers to diffusion and crystal nucleation that are described by an Arrhenius rate equation, exp(−E_a/k_B T), where E_a is the activation energy of either diffusion or nucleation, k_B is the Boltzmann constant, and T is absolute temperature [62]. Due to the rapid laser processing temperature, diffusion and nucleation can overcome the energy barrier more rapidly than conventional brazing and proceed more rapidly than reactions occurring just above the melting point of the metal.

[0037] In one embodiment, a brazing alloy is used for the first layer to the dissimilar substrate (ceramic or glass substrate), and then subsequent layers transition, either abruptly or gradually to a different material. One particular embodiment of this is to build on a substrate, like Si, and transition with a bonding layer to a material like copper, aluminum, or stainless steel. One application of this is to transition to a higher thermal and electrical conductivity material, like aluminum or copper, for heat transfer or electrical transport benefits. The interlayer can be an abrupt transition with one or more layers of the bonding powder or alloy and then transition to a different material, or the transition can be gradual with interlayers varying in composition from the bonding alloy or bonding powder mixture to the new mixture. The bonding from non-metal to metal can occur via intermetallic bonding or amorphous mixture of the two. The metal-to-metal bond can form via intermetallic formation or solid solution alloy formation at the interface. By controlling the processing parameters, it is even possible to print higher melting point materials on a lower-melting point substrate.

[0038] One embodiment uses the bonding alloy or bonding metal powder mixture to bond a substrate via the bonding braze to a subsequent metal. This bonding layer softens and the bulk phase melts at lower temperature than the layer on either side. This bonding layer can therefore be removed by application of heat. This enables the support build platform to be parted from the desired part. This is in contrast to the typical method of part separation that involves machining parts from the build plate via operations like bandsaws and wire electrostatic discharge machining. In a related alternate embodiment, the bonding alloy or bonding powder mixture can be used as internal support structure that will be softened or melted away during post-processing. Thus, the bonding alloy or bonding powder mixture can form the support that enables overhangs, yet also is easily removable via melting, rather than mechanical means. The bonding alloy or bonding powder mixture can be distributed via a stream or via a powder recoater process. The process can even be conducted in two steps, with one additive printer printing one material and a second additive printer printing the next layer, so that a multi-material powder bed fusion or multi-material directed energy deposition tool is not required.

[0039] In yet another embodiment, the bonding alloy or bonding powder can be printed directly on a metal, and then subsequently bonded via an oven to a dissimilar substrate (e.g., ceramic or glass). In a particular embodiment, the Sn₃Ag₄Ti alloy can be printed on steel, and then that can be bonded at elevated temperatures to a different metal or non-metal, including from the following possible combinations: oxides (e.g., silica glass, quartz, borosilicate glass, alumina, beryllia, ceria, zirconia, lithium aluminum silicates, gallium oxide, indium tin oxide, indium zinc oxide), silicides (e.g., molybdenum disilicide), nitrides, and carbides (e.g., silicon carbide), carbon materials (e.g., diamond, pyrolytic graphite, carbon nanotubes, graphene, fullerenes), borides (e.g., tungsten borides), arsenides (e.g., gallium arsenide), sulfides (e.g., zinc sulfide), gallium arsenide, stainless steel, copper and copper alloys, and aluminum and aluminum alloys. In yet another embodiment of the invention, a surface may already be coated or made of the bonding alloy and be subsequently additively manufactured on top of the surface.

[0040] The glass powder may be a low melting point glass, e.g., leaded glass or lead-free low melting point glass alternatives such as Hitachi Vaneetect or from Corning, JP2010184852A; U.S. Pat. Nos. 3,837,866A; 4,743,302A, WO2016175469A1. For example, the technology may be used to print a pattern of low melting point glass onto a higher melting point glass, for example to provide relief features on a glass surface, such as to provide tactile guidance on a touchscreen, binary (or digital) refractive lens structures, e.g., Fresnel lens type structures, and the like. A low melting temperature glass has a melting point below about 400° C.

[0041] In yet another embodiment, the substrate and/or powder can be coated in a metallization that promotes bonding and/or reduces surface fouling. The surface may be coated via techniques including evaporation, sputtering. The metallization can include elements X═Ti, Ta, Zr, V, Hf, Cr, Mo, W, Nb.

[0042] In several embodiments of this invention, a 3D pattern or mold can be used to produce the desired features on a ceramic or glass substrate. This mold can be made of a flexible and heat-resistant material like silicone and loaded with brazing alloy powder on the top layer to be bonded to the ceramic or glass substrate. This can be done layer-by-layer. Layers below this bonding alloy can be powder or solid metal to be added to the ceramic or glass substrate. This technique can then have thermal energy from a heat source, including a laser, a microwave or infrared heat source, bond and fuse the metal to the ceramic or glass substrate. The microwave has a greater absorption in the powder than semiconductor, so selectively absorbs more energy, thus not damaging the ceramic or glass. Subsequent layers or bonding to other metals can follow.

[0043] In several embodiments of the invention, the processing parameters of a specific bonding alloy powder (homogeneous or inhomogeneous) are determined as a function of the substrate, underlying layer, layer height, directed energy spot size, ambient gas, powder deposition methodology. To determine the ideal print properties, a print on the substrate with different power and scan rate features will be made, and the surface texture and mechanical strength of the alloy and interface are examined. This processing is examined for single and multiple exposures. Once the process for the first layer is determined, subsequent layers and transition layer processing parameters are determined in a similar manner. Methods of examining the print include profilometry to estimate contact angle, mechanical testing via macro mechanical testing and by solder ball shear or pull-off testing.

[0044] One embodiment creates surface texturing or voids or wicking texture to enhance phase-change heat transfer. One attractive way to improve heat transfer is to use phase-change, especially boiling and evaporation for cooling. Two-phase cooling via boiling has heat transfer coefficients orders-of-magnitude higher than single-phase liquid cooling, due to the large amount of energy required to vaporize liquids per unit weight. The rate of boiling heat transfer is a function of how many bubble generating sites are available. Scratches and pits often act as nucleation sites, as the crevices encourage bubble growth by reducing the energy required for bubbles to nucleate compared to a flat surface. One way they do this is by trapping nuclei of bubbles that reduce the energy of bubble generation, and increase the heat transfer in the onset boiling regime. Reentrant cavities also delay the critical heat flux, which is the maximum heat flux before any further increase in surface temperature will actually have reduced heat flux due to water vapor blanket fully enveloping the surface, which insulates the surface. Therefore, one embodiment of this invention is to intentionally create texturing for bubble nucleation. An additional embodiment further coats the surface to make bubble liftoff easier and liquid replenishment of bubble sites easier. This can involve deposition via solution, chemical vapor deposition, physical vapor deposition, and/or atomic layer deposition.

[0045] In another embodiment, wicks for evaporative cooling and heat pipes are mode using this bonding alloy or bonding powder mixture. While there are many varieties of heat pipes, the basic variety has two primary components: 1) a wick that draws refrigerant into the evaporator by capillary pressure and 2) a condenser that condenses the vaporized refrigerant. The effective thermal conductivity of typical heat pipes exceed that of copper by several times.[63] One embodiment of this invention is directly producing these wicks on the active electronic devices substrate. In an alternative embodiment these wicks are used for evaporative cooling in an open system. The evaporator features could be printed via this technique and a lid can seal and integrate this into a heat-pipe system. It can be sealed to the substrate with adhesive or melting a material that bonds well to the substrate. The lid can be made of any number of materials, including polymers and metals.

[0046] An alternative embodiment is to create microchannels. These microchannels can be used for cooling or for microfluidic integration. The microchannels can also be used to make integrated cooling channels for non-wicked heat pipes, like oscillating heat pipes and for two-phase heat transfer devices called vapor chambers. The microchannels can be produced by this technique and a lid that can seals to the chip and has flow inlets and outlets can be used.

[0047] Another embodiment uses the bonding alloy or bonding powder mixture to fabricate electrical connections to the substrate. This process can involve transitioning from the bonding metal alloy to a different metal for reasons such as improved electrical conductivity. In some embodiments, electrical connections and thermal heat sinking can occur on the same electrical device. On certain substrates these connections could be made to transparent conductive material (e.g., indium tin oxide, indium zinc oxide, graphene).

[0048] It is therefore an object to provide a method for forming a metal structure bonded to a dissimilar substrate, comprising: providing a substrate having a bonding surface; depositing a powder comprising components that, when heated to at least a melting temperature, melts and chemically reacts with the substrate to form an interlayer which adheres the melted powder to the dissimilar substrate; heating a portion of the powder deposited on the substrate with a localized energy source, the localized energy source being dynamically controlled to regionally melt the portion of the powder substantially without melting all of the powder and without bringing the substrate into thermal equilibrium, said heating being sufficient to form the interlayer which adheres the melted powder to the dissimilar substrate; and cooling the regionally melted portion of the powder to form a solid layer, wherein the solid layer is adhered to the dissimilar substrate.

[0049] A device, comprising a fused powder conductive metal alloy, wherein the alloy forms an interlayer comprising at least one intermetallic or intermetallic-like compound component with a dissimilar material supporting surface, the fused powder being formed on the dissimilar material supporting surface as a conductive trace separated from at least one other trace by an insulating region, the dissimilar material supporting surface being part of a substrate having a heat sensitive structure which is degraded at a temperature lower than a melting point of the conductive metal alloy.

[0050] The cooling may occur concurrently with heating of a different portion of the powder deposited on the substrate with the localized energy source, to regionally melt the different portion of the powder.

[0051] The localized energy source may have a heating diameter, and the melted portion of the powder is confined to a region extending laterally along the surface no more than three times the heating diameter. The localized energy source has an energy density of about 40 J/mm³. The localized energy source may have an energy density of less than about 150 J/mm³.

[0052] The method may further comprise reheating the portion of the powder deposited on the substrate with the localized energy source, to enhance formation of the interlayer which adheres the melted powder to the dissimilar substrate, and subsequently cooling the regionally remelted portion of the powder to reform the solid layer.

[0053] The localized energy source may heat the region above the melting temperature for a duration of less than about 60 seconds, or 30 seconds, or 20 seconds, or 20 seconds, or 5 seconds, or 2.5 seconds, or 1 second, or about 100 milliseconds, or 10 milliseconds, or 1 millisecond, or 100 microseconds, or 25 microseconds, for example.

[0054] The localized energy source may heat the region for a duration of less than about 60 seconds, or 30 seconds, or 20 seconds, or 20 seconds, or 5 seconds, or 2.5 seconds, or 1 second, or about 100 milliseconds, or 10 milliseconds, or 1 millisecond, or 100 microseconds, or 25 microseconds, for example.

[0055] The localized energy source may be pulsatile or continuous. The localized energy source may be dynamically repositioned over the surface, during exposure or between pulses of exposure. The powder may comprise a metal powder, e.g., having a melting temperature of less than 1600° C., or 1500° C., or 1400° C., or 1300° C., or 1250° C., or 1200° C., or 1100° C., or 1000° C., or 900° C., or 800° C., or 700° C., or 600° C., or 500° C., or 400° C., or 375° C., or 350° C., or 325° C., or 300° C., or 290° C., or 285° C., or 280° C., or 270° C., or 260° C., or 250° C., or 240° C., or 230° C., or 220° C., or 210° C., or 200° C., or 190° C., or 180° C., or 170° C., or 160° C., 150° C., or 140° C., or 130° C., or 125° C., or 120° C., 110° C., 100° C., or 90° C., or 80° C., or 79° C., or 75° C., for example.

[0056] The powder may chemically react with the dissimilar substrate to form an intermetallic or intermetallic-like compound. The powder may chemically react with the dissimilar substrate to form a metal carbide or metal silicide compound. The powder may chemically react with the dissimilar substrate in an anoxic or inert environment, such as argon, helium or nitrogen gas.

[0057] At least one of the powder and the dissimilar substrate may be flammable in air, especially under conditions of focused laser or electron beam irradiation. At least one of the powder and the dissimilar substrate may be pattered by modulating a flow of reactive gas, such that regions exposed to the focused energy beam in the presence of the reactive gas have different properties than regions exposed to the focused energy beam in the absence of the reactive gas. The modulated property may be porosity, hydrophilicity/hydrophobicity, adhesion to subsequent layers of fused metal or metal particles, bubble liftoff, surface roughness, electrical conductivity, thermal conductivity, optical refractive properties, optical reflective properties, optical absorption properties, frictional coefficient, chemical reactivity, wear-resistance, etc.

[0058] The powder may melt to form a metal layer having less than about 1% void space. The melted powder may have a density of at least 99% of a homogeneous solid formed of the same composition as the powder.

[0059] The heating may comprise selective laser melting (SLM), electron beam exposure, or other techniques.

[0060] The dissimilar substrate may comprise pyrolytic carbon, graphite, silicon, an integrated circuit wafer, stainless steel, 316L stainless steel, a gallium arsenide wafer, an integrated circuit formed on a semiconductor wafer, a microprocessor formed on a silicon wafer, silicon carbide, diamond, a diamond-like coating, gallium oxide, a material with a conductive transparent substrate (indium tin oxide, indium zinc oxide, graphene), silica glass, quartz, borosilicate glass, molybdenum disilicide, tungsten borides, dissimilar metal, a heatsink or other materials, devices or structures.

[0061] The solid layer may be part of a stack of solid layers formed above the bonding surface.

[0062] The stack of solid layers may define a bounded space. The bounded space may define a fluid flow channel. The fluid flow channel may comprise a microchannel heat exchanger. The fluid flow channel may comprise a phase change heat pipe.

[0063] The stack of solid layers may be homogenous or heterogeneous. The stack of solid layers may have a composition gradient. The stack of solid layers may have a composition discontinuity. The stack of solid layers may comprise a low melting point solder.

[0064] The dissimilar substrate may be non-metallic and the solid layer may be metallic.

[0065] The solid layer may have a first melting point, and a second solid layer is formed over the solid layer having a second melting point, the second melting point being higher than the first melting point, wherein heating the dissimilar substrate to a temperature between the first melting point and the second melting point causes a loss of material integrity between the dissimilar substrate and the second solid layer, making the second solid layer separable from the dissimilar substrate.

[0066] The preferred embodiment is a localized energy source that may comprise a laser beam or an electron beam. Alternative embodiments could use an energy source that is less localized, like a microwave energy source, an infrared heating element, or a heated stylus (eg soldering iron tip), possibly with a template or mold providing finer detailing on where material should bond to the substrate.

[0067] The dissimilar substrate and the solid layer may have similar coefficients of thermal expansion, wherein thermal mismatch does not cause delamination over a temperature range of −25° C. to +125° C. The dissimilar substrate and the solid layer may have different coefficients of thermal expansion, wherein thermal mismatch is sufficient to reliably cause delamination at a temperature under 250° C.

[0068] The pattern produced can have features that are sized small enough that the thermal stresses do not lead to interfacial delaminations. The features can be printed in smaller units at a time so the heat buildup and thermal stresses from cool-down of melt are below the interfacial bond failure stress limit.

[0069] The powder may comprise a metal having between about 1% and 10% by weight aggregate of at least one of Ti, Zr, V, Nb, Hf, Ta, Mo, Cr, and W. Various metals form silicide compounds, including: Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Y, Zr, Nb, Mo, Ru, Rh, Pd, Hf, Ta, W, Re, Os, Jr, Pt, La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Yb, Lu, Th, U, Np, Pu, Am, and Cm. Therefore, these components may be present within the powder to be processed, and potentially form silicides that enhance adhesion to a silicon substrate. Some of these would only be useful in very particular circumstances, for example, Np, Am and Cm might find application in high-cost tolerant situations where one seeks a future release of the solid metal from the silicon, as might result from radioactive decay of the silicides that promote adhesion. Some of these same silicide forming elements also promote bonding to silica materials like ceramics composed of silica, quartz, borosilicate glasses, lithium aluminum silicate glass-ceramics.

[0070] The powder may comprise a solder alloy selected from the group consisting of at least two of Sn, Pb, Ag, Cu, Sb, Bi, In, Zn, Cd, Au, Ni, Si, Ge, Si, and Al. The powder may comprise a solder alloy selected from the group consisting of: InSn (e.g., In₅₂Sn₄₈, In₆₀Sn₄₀, In₅₀Sn₅₀, In₄₂Sn₅₈), InCd (e.g., In₇₄Cd₂₆), BiPbInCdSn (e.g., Bi_44.7Pb_22.6In_19.1Cd_5.3Sn_8.3), InBiSn (e.g., In₅₁Bi_32.5Sn_16.5), InBiCd (e.g., In_61.7Bi_30.8Cd_7.5), BiPbSnIn (e.g., Bi₄₉Pb₁₈Sn₁₂In₂₁), BiPbSnCd (e.g., Bi₅₀Pb_26.7Sn_13.3Cd₁₀), BiSnIn (e.g., Bi₅₆Sn₃₀In₁₄), BiPbSn (e.g., Bi₅₂Pb₃₂Sn₁₆, Bi₅₀Pb_31.2Sn_18.8), BiPb (e.g., Bi₅₈Pb₄₂), SnPbBi (e.g., Sn₄₆Pb₄₆Bi₈), InSnPbCd (e.g., In₇₀Sn₁₅Pb_9.6Cd_5.4), SnPbIn (e.g., Sn₅₄Pb₂₆In₂₀, Sn_37.5Pb_37.5In₂₅, Sn₇₀Pb₁₈In₁₂), BiSnAg (e.g., Bi₅₇Sn₄₂Ag₁), BiSn (e.g., Bi₅₆Sn_42, Bi₅₈Sn₄₂), SnBiPb (e.g., Sn₄₈Bi₃₂Pb₂₀, Sn₄₃Pb₄₃Bi₁₄), CdSn (e.g., Cd₇₀Sn₃₀), InPbAg (e.g., In₈₀Pb₁₅Ag₅), InAg (e.g., In₉₇Ag_3, In₉₀Ag₁₀), SnPbCd (e.g., Sn_51.2Pb_30.6Cd_18.2), InPb (e.g., In₇₅Pb₂₅, In₇₀Pb_30, In₆₀Pb_40, In₅₀Pb₅₀, Pb₇₅In₂₅), In, PbSnZn (e.g., Pb₆₃Sn₃₄Zn₃), SnZnInBi (e.g., Sn_86.5Zn_5.5In_4.5Bi_3.5), SnInAg (e.g., Sn_77.2In₂₀Ag_2.8, Sn_86.9In₁₀Ag_3.1, Sn_91.8In_4.8Ag_3.4, Sn₈₈In_8.0Ag_3.5Bi_0.5), SnZnCd (e.g., Sn₄₀Zn₂₇Cd₃₃), SnPbZn (e.g., Sn₃₀Pb₅₀Zn₂₀), PbSnAg (e.g., Pb₅₄Sn₄₅Ag_1, Sn₆₂Pb₃₆Ag₂, Pb₈₀Sn₁₈Ag₂, Pb₉₆Sn₂Ag₂, Pb₈₈Sn₁₀Ag₂, Pb₉₂Sn_5.5Ag_2.5, Pb₉₀Sn₅Ag₅, Pb_93.5Sn₅Ag_1.5, Pb_95.5Sn₂Ag_2.5), SnZnIn (e.g., Sn_83.6Zn_7.6In_8.8), PbSn (e.g., Pb₉₀Sn₁₀, Pb₈₅Sn₁₅, Pb₈₀Sn₂₀, Sn₆₃Pb₃₇, Sn₇₀Pb₃₀, Sn₉₀Pb₁₀, Sn₆₃Pb₃₇P_0.0015-0.04, Sn₆₂Pb₃₇Cu₁, Sn_97.5Pb₁Ag_1.5,), SnZnBi (e.g., Sn₈₉Zn₈Bi₃), SnZn (e.g., Sn₉₁Zn_9, Sn₈₅Zn_15, Sn₆₀Zn_40, Zn₇₀sn_30, Zn₆₀Sn_40, Sn₅₀Zn₄₉Cu₁, Sn₉₀Zn₇Cu₃), SnBiAg (e.g., Sn_91.8Bi_4.8Ag_3.4), SnAgCu (e.g., Sn_96.5Ag_3.0Cu_0.5, Sn_95.5Ag_4.0Cu_0.5, Sn_95.8Ag_3.5Cu_0.7, Sn_95.6Ag_3.5Cu_0.9, Sn₉₉Cu_0.7Ag_0.3, Sn_96.2Ag_2.5Cu_0.8Sb_0.5, Sn_90.7Ag_3.6Cu_0.7Cr₅, Sn₉₅Ag_3.5Zn₁Cu_0.5, Sn_95.5Cu₄Ag_0.5, Sn₉₇Cu_2.75Ag_0.25), SnAu (e.g., Sn₉₀Au₁₀), SnAg (e.g., Sn_96.5Ag_3.5—Sn₉₃Ag₇), SnCu (e.g., Sn_99.3Cu_0.7, Sn₉₇Cu₃), SnPbZn (e.g., Sn₃₃Pb₄₀Zn₂₈), Sn, SnSb (e.g., Sn₉₅Sb₅—Sn₉₉Sb₁), SnAgSb (e.g., Sn₆₄Ag₂₅Sb₁₀), PbIn (e.g., Pb₈₁In₁₉, Pb₇₀In₃₀, Pb₇₅In₂₅, Pb₉₀In₅Ag₅, Pb_92.5In₅Ag_2.5, Pb_92.5In₅Au_2.5), CdZn (e.g., Cd_82.5Zn_17.5, Cd₇₀Zn₃₀, Cd₆₀Zn₄₀, Zn₉₀Cd₁₀, Zn₆₀Cd₄₀, Cd₇₈Zn₁₇Ag₅), Bi, AuSn (e.g., Au₈₀Sn₂₀), PbSbSn (e.g., Pb₈₀Sb₁₅Sn₅), PbAg (e.g., Pb_94.5Ag_5.5—Pb₉₆Ag₄, Pb₉₇Ag_1.5Sn₁, Pb_97.5Ag_2.5), CdAg (e.g., Cd₉₅Ag₅), AuSi (e.g., Au₉₈Si₂, Au_96.8Si_3.2), ZnAl (e.g., Zn₉₅Al₅), ZnSn (e.g., Zn₉₅Sn₅), Zn, AuIn (e.g., Au₈₂In₁₈), AuGe (e.g., Au_87.5Ge_12.5). The powder may comprise Sn₃Ag₄Ti, or an AgCuTi alloy. The powder may comprise an Ag₂₁Cu₅X alloy where X═Ti, Ta, Zr, V, Hf, Cr, Mo, W, and Nb. The powder may comprise a Cu alloy having between about 1% and 10% by aggregate weight of X═Ti, Ta, Zr, V, Hf, Cr, Mo, W, and Nb. The powder may comprise an Al alloy having between about 1% and 10% by aggregate weight of X═Ti, Ta, Zr, V, Hf, Cr, Mo, W, and Nb.

[0071] The localized energy source may be a 1064 nm Yb-fiber laser. A position of the localized energy source may be controlled by a galvanometer mirror system. The localized energy source may have a heating zone of less than 300 μm deep.

[0072] The dissimilar substrate may comprise at least one of silicon and graphite, with a solid layer formed of Sn₃Ag₄Ti, and a second solid later of 316L stainless steel formed on the Sn₃Ag₄Ti.

[0073] The heating and cooling may be repetitively cycled to reduce a contact angle.

[0074] The heating and cooling may be repetitively cycled to increase a mechanical strength.

[0075] The heating and cooling may be repetitively cycled to relieve residual thermal stress.

[0076] The solid layer bonded to the dissimilar substrate may comprise a heat spreader for a heat dissipative device.

[0077] It is another object to provide a method of forming a heatsink for an integrated circuit, comprising: depositing a metallic powder on an integrated circuit substrate; and locally heating the metallic power to a sufficient temperature to melt the metallic powder with focused energy, having limited duration at a particular region to avoid heat-induced functional damage to the integrated circuit, and cooling the melted metallic powder to form a solid layer, to form an adherent bond between the integrated circuit substrate and the solid layer.

[0078] The adherent bond may comprise a metal silicide component interlayer.

[0079] The locally heating may comprise exposing the metallic powder to radiation pulses, and/or spatially scanned radiation.

[0080] The locally heating may remelt and subsequently cool regions of the solid layer.

[0081] The method may further comprise depositing a second metallic powder over the solid layer, the second metallic powder being different from the metallic powder; and locally heating the second metallic power to a sufficient temperature to melt the second metallic powder, substantially without heat-induced functional damage to the integrated circuit, while forming an alloy interlayer between the melted second metallic powder and the solid layer.

[0082] The silicon wafer (or other substrate) may be cleaned by a process selective from the group consisting of at least one of a chemical, a mechanical, and an ablative cleaning step.

[0083] It is a further object to provide a method for forming a selectively melted metal structure, comprising: providing a substrate having a bonding surface; depositing a first powder comprising components of a fused low melting temperature metal, having a composition that, when heated, chemically reacts with the substrate; heating the first powder, on the substrate, with localized energy source to melt the powder and the melted low melting temperature metal, and to react with the bonding surface, sufficient to form a bonding interlayer; depositing a second powder comprising components of a high melting temperature metal, having a composition that, when heated, forms an alloy interlayer with the lower melting temperature metal substrate; and heating the second powder, on the fused low melting temperature metal, with localized energy pulses to fuse the second powder, and to alloy with the fused low melting temperature metal.

[0084] The substrate mat be further heated to at least soften the fused low melting temperature metal while maintaining the fused high melting temperature metal as a solid; and the solid fused high melting temperature metal then removed from the substrate.

[0085] After removing the solid fused high melting temperature metal from the substrate, the substrate may be reused by: depositing a third powder comprising components of a fused low melting temperature metal, having a composition that, when heated, chemically reacts with the substrate; and heating the third powder, on the substrate, with localized energy source to melt the powder and the melted low melting temperature metal, and to react with the bonding surface, sufficient to form a bonding interlayer.

[0086] It is another object to provide a metal alloy powder for use in additive manufacturing, comprising a particles of metal alloy, and particles which form non-metal inclusions, wherein a fused volume of the metal alloy powder formed by localized heating has a plurality of surface re-entrant cavities configured to promote bubble nucleation in a heat transfer fluid.

[0087] The configuration of the surface re-entrant cavities may be controllable by a modulation and a power setting of a laser power source.

[0088] It is a still further object to provide a heat transfer device comprising the fused volume of the metal alloy powder, formed by localized heating having the plurality of surface re-entrant cavities configured to promote bubble nucleation in the heat transfer fluid.

[0089] It is also an object to provide a method for forming a structure bonded to a substrate, comprising: providing a substrate; forming an interlayer by chemical reaction on the substrate, between the substrate and a metal layer; depositing a metallic powder on the metal layer; heating a portion of the metallic powder deposited on the substrate with a localized energy source in a localized heating region, the localized energy source being dynamically controlled to regionally melt the portion of the metallic powder substantially while leaving an adjacent portion of the metallic powder unmelted, and without bringing the substrate underneath the localized heating region into thermal equilibrium; and cooling the regionally melted portion of the metallic powder to form a solid layer.

[0090] The cooling may occur concurrently with heating of a different portion of the metallic powder deposited on the surface with the localized energy source, to regionally melt the different portion of the metallic powder.

[0091] The localized energy source may be operated continuously and is dynamically repositioned over the surface. The metallic powder may consist essentially of a metal or metal alloy powder. The powder may chemically react with the surface of the substrate to form at least one of an intermetallic compound, a metal carbide compound, a metal nitride compound, a metal boride compound, and a metal silicide compound. A location of the localized heating region may be controlled over time to selectively melt the powder into a predefined patterned layer having gaps between portions of the solid layer. The heating may comprise selective laser melting (SLM). The substrate may comprise a semiconductor. The surface of the substrate may comprise an aluminum or copper layer.

[0092] The method may further comprise forming a stack of layers over the solid layer above the bonding surface, by sequentially depositing a powder on an upper surface and melting the powder, in a predetermined pattern, to form a three-dimensional structure which adheres to the substrate.

[0093] It is a further object to provide a method of forming a structure on an integrated circuit, comprising: depositing a powder on a surface of a substrate comprising an integrated circuit; and locally heating the powder to a sufficient temperature to melt the powder with focused energy, having limited duration at a particular region to avoid heat-induced functional damage to the integrated circuit, and cooling the melted powder to form a solid layer, wherein an adherent bonding layer is present between the substrate and the solid layer comprising a chemical reaction product distinct from a composition of the surface and a composition of the solid layer.

[0094] The adherent bonding layer may comprise an interlayer selected from the group consisting of an intermetallic compound, a metal silicide, a metal carbide, a metal boride, and a metal nitride, and the solid layer comprises a metal or metal alloy, and the method further comprise forming a stack of additional solid layers over the solid layer in a regional pattern to form a three dimensional structure having at least one space over the substrate between respective portions of the regional pattern, while avoiding heat-induced functional damage to the integrated circuit.

[0095] Another object of the invention provides a device, comprising: a fused layer, formed by a process comprising: depositing a powder on a supporting surface of a substrate, comprising particles; and locally heating a portion of the powder on the supporting surface with a focused energy beam, substantially without achieving thermal equilibrium in the substrate, to fuse the locally heated portion of the powder to form an adhesion interlayer.

[0096] The adhesion layer may be formed substantially without concurrently fusing a non-locally heated portion of the powder, configured as a region-specific pattern.

[0097] The adhesion interlayer may comprise a heating-induced chemical reaction product of the supporting surface of the substrate and the powder

[0098] The powder may further comprise particles which form inclusions in the fused volume of powder, wherein after locally heating, the powder, an exposed surface of the fused volume of powder comprises a plurality of surface re-entrant cavities.

[0099] The region-specific pattern of the device may be configured as a heat sink.

[0100] The fused volume may have a surface with adjacent regions of heterogeneous aqueous fluid wetting, wherein regions with high wettability promote aqueous liquid flow to bubble generation sites, and regions with low wettability promote bubble liftoff. The region-specific pattern may define a circumferential wall of a microchannel configured to guide fluid flow.

[0101] The powder may comprise a metal alloy, and between about 1% to about 10% aggregate weight, per weight of the metal alloy, of a reactive element that bonds actively to the substrate surface selected from the group consisting of Ti, Ta, Zr, V, Hf, Cr, Mo, W, and Nb.

[0102] A further object of the invention provides a manufactured structure, comprising: a substrate; an interface layer, comprising a chemical reaction product of a surface of the substrate and a metallic composition; and a solid layer, formed over the interface layer from fused portions of the powder, in a regional pattern having at least one void region over the substrate.

[0103] The substrate may comprise an integrated circuit having a deposited metal layer, the solid layer is metallic, the fused interface layer comprises an intermetallic composition, and the regional pattern is configured as a heatsink for the integrated circuit.

[0104] The manufactured structure may further comprise an additional solid layer formed on the solid layer by regional heating of a powder.

[0105] The additional solid layer may be formed in a three dimensional pattern having a gap between selectively formed regions of the regional pattern.

[0106] The solid layer may be formed by fusion of a powder that chemically reacts with the surface to form the interface layer comprising at least one of an intermetallic compound, a metal carbide compound, a metal nitride compound, a metal boride compound, and a metal silicide compound.

[0107] The substrate may comprise a semiconductor. The semiconductor may be configured as an integrated electronic circuit, and wherein the solid layer is configured as a set of electrically-isolated electrical interconnects to the integrated electronic circuit.

[0108] A still further object provides an adhesive interlayer between a substrate and a fused metal alloy powder, comprising a chemical reaction product comprising at least one of a metal silicide, a metal carbide, a metal boride, and a metal nitride with a respective substrate, the chemical reaction product forming a shear resistant layer which causes the fused metal alloy powder to adhere to the substrate.

[0109] The chemical reaction product may be selected from the group consisting of an intermetallic compound, an intermetallic-like compound, or a chalcogen bond compound.

[0110] It is another object to provide a device, comprising: a fused metal alloy, formed by a process comprising: depositing a powder on a supporting surface of a dissimilar substrate, comprising particles of metal alloy wherein the powder is reactive under heating with the supporting surface of the dissimilar substrate to form an interlayer comprising at least one intermetallic or intermetallic-like compound component; and locally heating the powder on the supporting surface with a focused energy beam, substantially without achieving thermal equilibrium, to fuse the volume of the powder and form the interlayer.

[0111] The powder may further comprise particles which form non-metal inclusions in the fused volume of powder, wherein after locally heating, the powder, an exposed surface of the fused volume of powder comprises a plurality of surface re-entrant cavities. A configuration of the re-entrant cavities may be controlled by a modulation and power setting of the focused energy source. The device may be configured as a heat sink, a heat pipe, or a heat spreader.

[0112] The device may have a porous surface of the fused volume configured to promote fluid wicking. The porous surface of the fused volume may be configured to promote heat transfer by fluid wicking.

[0113] The fused volume may have a surface with adjacent regions of heterogeneous aqueous fluid wetting, wherein regions with high wettability promotes aqueous liquid flow to bubble generation sites, and regions with low wettability promote bubble liftoff. The adjacent regions of heterogeneous aqueous fluid wetting may be defined by a selective coating on the surface. The adjacent regions of heterogeneous aqueous fluid wetting may be defined by a selective surface treatment. The adjacent regions of heterogeneous aqueous fluid wetting may be defined by a selective control over the focused energy beam during the locally heating. The adjacent regions of heterogeneous aqueous fluid wetting may be defined by a selective control over an atmosphere during the locally heating.

[0114] The locally heating may be conducted in an inert gas.

[0115] The locally heating may be controlled to define a microchannel configured to guide fluid flow within the fused volume of powder, the microchannel being covered by at least one layer above the fused volume of powder.

[0116] The dissimilar substrate may be formed of a dissimilar metal with respect to the fused metal alloy.

[0117] The device may further comprise a metal structure bonded to the dissimilar substrate. The dissimilar substrate may be formed of a non-metal or a metal.

[0118] The fused volume may be separated from the dissimilar substrate after formation.

[0119] The device may further comprise at least one additional layer of metal alloy formed over the fused volume of the powder, the at least one additional layer of metal alloy having a higher melting point than the fused volume of the powder.

[0120] The device may further comprise at least one metal layer formed over the fused volume of the powder by a process selected from the group consisting of: sputtering, plasma coating, electrodeposition, and evaporation.

[0121] The powder may consist essentially of an SnAgX alloy, where X is a reactive element selected from the group consisting of Ti, Ta, Zr, V, Hf, Cr, Mo, W, and Nb in an amount of between about 1% to about 10% by weight, where Ag is about 3% by weight and Sn is the balance.

[0122] The powder may consist essentially of an AgCuX alloy, where X is a reactive element selected from the group consisting of Ti, Ta, Zr, V, Hf, Cr, Mo, W, and Nb in an amount of between about 1% to about 10% by weight, where Cu is about 35% by weight and Ag is the balance.

[0123] The powder may consist essentially of a Cu alloy comprising copper and additional alloying elements, and optional non-metallic particles, wherein the additional alloying elements are provided in an effective amount to reactively bond with dissimilar substrate to form the intermetallic or intermetallic-like compound, and to lower a melting point of the Cu alloy with respect to Cu.

[0124] The additional alloying elements may comprise at least one of Ti, Ta, Zr, V, Hf, Cr, Mo, W, and Nb in weight percentages from about 1-10 wt %, the Cu alloy being at least 50% by weight Cu.

[0125] The powder may comprise a mixture of metal powder and non-metal reinforcements.

[0126] The locally heating may be performed by controlling a focused laser, to determine: an optimal laser processing power, an optimal scan rate, and an optimal fused volume thickness, for each of a plurality of layers of powder formed on the dissimilar substrate, by rastering multiple scan rates and laser processing power on test parts for each layer thickness, and inspecting the test parts to determine the optimum processing conditions, and subsequently employing the determined optimum processing conditions on other parts. The testing may comprise a visual inspection and/or thermal testing of the test parts.

[0127] The powder may comprise of a powder with a homogeneous concentration of an alloying mixture, or a powder with a heterogeneous metal powder.

[0128] It is another object to provide a metal alloy powder for selective laser melting additive manufacturing, comprising: optional non-metallic inclusion particles; particles which comprise components that fuse to form an alloy having a thermal conductivity of at least 17 W/mK at 25° C., and forms at least one of metal silicides, metal carbides, and metal nitrides with a respective non-metallic substrate comprising silicon, carbon, or nitrogen, in an interlayer region with the non-metallic substrate.

[0129] The powder may comprise the metal alloy, and between about 1% to about 10% aggregate weight, per weight of the metal alloy, of a reactive element that bonds actively to the substrate surface. The reactive element may be one of more element selected from the group consisting of Ti, Ta, Zr, V, Hf, Cr, Mo, W, and Nb. The reactive element may facilitate bonding to a substrate selected from the group consisting of Si, SiC, SiN, graphite, diamond, carbon nanotubes, graphene, fullerenes, GaN, GaAs, βGa₂O₃, gallium oxide, Al₂O₃, and SiO₂ (glass and quartz), silica glass, quartz, borosilicate glass, aluminosilicate glass, lithium aluminum silicates, indium tin oxide, indium zinc oxide, molybdenum disilicide, tungsten boride, gallium arsenide, zinc sulfide, beryllia, ceria, zirconia, indium tin oxide, and indium zinc oxide.

[0130] In certain embodiments, additively manufactured metal structures are formed onto glasses and ceramics by directed energy deposition (e.g., laser beam, electron beam) that fuses a metal alloy onto a ceramic or glass substrate. This bond for an oxide-based ceramic or glass will occur via diffusional bonding (e.g., titanium oxides and titanium silicides forming from Ti in bonding alloy bonding to silica-based materials). Vacuum or protective gas such as argon, nitrogen might be used. After deposition of one or more layers of the brazing alloy, the material can be switched to other metals such as stainless steel, titanium alloys, copper alloys, aluminum alloys to build various structures. The thickness of the brazing alloy is a function of the thermal stress to be resisted and interfacial strength of the bond to the substrate. The brazing alloy in this process acts as an interface material and has components that bond to both glass or ceramic and the subsequent metal, unless a structure of the bonding alloy is desired. Because the laser exposure time is very short and high temperatures are reached, rapid bonding is enabled compared to conventional bonding. Moreover, because only a small section of the layer is molten at a time, the stresses at the interfaces can be reduced compared to a non-locally bonded interface, where the entire material is bonded at the same time. Furthermore, most metal have a greater coefficient of thermal expansion than ceramics and glasses, so the cooldown from the molten state can apply a compressive residual stress. In the case of laser heating, the absorption of the laser by the glass can affect how hot the glass substrates can get, and thus the residual stress upon cooling. Because absorption is a function of wavelength, the choice of laser wavelength is another variable that can be tuned to minimize residual stress upon cooling.

[0131] The powder bonds may form a metal oxide that diffusion bonds to the substrate.

[0132] The dissimilar substrate may comprise a substrate formed principally (e.g., >90% by weight) of silica borosilicate glasses; quartz; doped quartz, borosilicate, soda-lime glass, potash-lime glass, lead glass, flint glass, aluminosilicate glass, alumina, lithium aluminum silicate, beryllia, zirconia, gallium oxide, gallium aluminum oxide, gallium nitride, germanium oxide, silica-germania, germanium-oxide glass (alumina and germanium dioxide), fluoride glass, phosphate glass, borate glass, chalcogenide glass, indium tin oxide (ITO), an indium antimony oxide, indium oxide, indium zinc oxide, molybdenum disilicide, tungsten boride, tungsten carbide, or zinc sulfide for example.

[0133] The technology may be used to apply coatings to substrates, which may be homogeneous, heterogeneous, or patterned in two or three dimensions. The coating and/or substrate may be glass. Further, because the technology forms a chemically modified layer on the substrate, the technology may represent a treatment, such as a chemical strengthening, of the substrate.

[0134] For example, the known Corning® Gorilla® glass, AGC Inc. Dragontail®, or Schott AG Xensation®, chemically strengthened alkali-aluminosilicate glass may be formed by providing a potassium-rich coating on the base glass, and heating the interface during process to cause ion exchange, and prestress in the glass. As described in U.S. Pat. Nos. 7,666,511, 4,483,700 and 5,674,790, Corning Gorilla glass is made by fusion drawing a glass sheet and then chemical strengthening of the glass sheet. Corning Gorilla glass has a relatively deep depth of layer (DOL) of compressive stress, and presents surfaces having a relatively high flexural strength, scratch resistance and impact resistance.

[0135] See, U.S. Pat. Nos. 10,196,295; 10,195,643; 10,181,017; 10,173,916; 10,166,744; 10,162,084; 10,137,667; 10,116,777; 10,082,605; 10,051,753; 10,008,870; 9,933,820; 9,932,663; 9,931,817; 9,908,803; 9,887,066; 9,871,176; 9,850,160; 9,826,652; 9,815,144; 9,789,665; 9,774,192; 9,769,573; 9,729,187; 9,724,727; 9,676,653; 9,661,423; 9,655,293; 9,611,167; 9,599,766; 9,565,910; 9,564,938; 9,522,836; 9,512,029; 9,505,648; 9,477,346; 9,475,947; 9,471,172; 9,468,317; 9,446,979; 9,435,915; 9,434,633; 9,407,746; 9,369,553; 9,362,972; 9,351,083; 9,339,993; 9,308,616; 9,290,407; 9,287,916; 9,284,212; 9,264,090; 9,258,651; 9,231,410; 9,220,328; 9,102,007; 9,048,665; 8,994,695; 8,983,098; 8,980,115; 8,976,997; 8,974,105; 8,907,871; 8,883,314; 8,844,782; 8,842,358; 8,789,998; 8,708,458; and 8,586,492; 8,436,833. See also, U.S. Pat. Nos. 10,002,685; 10,023,495; 10,065,885; 10,117,806; 10,117,810; 10,123,947; 10,134,766; 10,135,002; 10,170,500; 10,170,726; 10,172,695; 10,202,216; 4,888,127; 5,099,759; 5,194,161; 5,628,945; 5,952,253; 5,993,701; 6,119,483; 6,128,918; 6,187,700; 6,300,263; 6,300,389; 6,360,562; 6,377,729; 6,423,387; 6,427,489; 6,430,965; 6,526,778; 6,537,648; 6,555,299; 6,593,061; 6,620,861; 6,643,442; 6,750,023; 6,771,009; 6,800,574; 6,845,635; 6,852,010; 6,866,929; 6,871,514; 6,881,483; 6,914,024; 7,040,953; 7,169,489; 7,235,736; 7,299,749; 7,312,168; 7,321,012; 7,358,008; 7,384,680; 7,405,326; 7,420,065; 7,438,990; 7,514,174; 7,521,567; 7,521,928; 7,629,480; 7,631,518; 7,635,617; 7,666,568; 7,678,668; 7,691,279; 7,727,846; 7,825,007; 7,838,130; 7,851,804; 7,867,907; 7,964,262; 7,977,405; 7,989,068; 8,007,557; 8,066,946; 8,114,211; 8,119,267; 8,119,315; 8,339,837; 8,357,311; 8,357,731; 8,361,873; 8,367,224; 8,414,424; 8,435,477; 8,455,331; 8,497,312; 8,546,161; 8,552,088; 8,568,684; 8,586,199; 8,592,057; 8,610,120; 8,617,994; 8,628,987; 8,634,228; 8,654,566; 8,697,322; 8,765,837; 8,766,253; 8,783,063; 8,790,768; 8,790,793; 8,797,487; 8,815,974; 8,829,528; 8,884,284; 8,907,879; 8,916,406; 8,919,150; 8,926,389; 8,932,060; 8,932,184; 8,951,650; 8,957,468; 8,987,728; 8,988,116; 9,034,442; 9,035,867; 9,040,975; 9,070,399; 9,082,861; 9,102,566; 9,105,869; 9,112,086; 9,112,168; 9,142,681; 9,145,363; 9,168,573; 9,175,174; 9,184,355; 9,186,295; 9,198,829; 9,241,869; 9,260,390; 9,272,946; 9,287,521; 9,333,148; 9,359,513; 9,406,698; 9,408,781; 9,474,688; 9,474,689; 9,478,422; 9,490,350; 9,490,351; 9,494,829; 9,511,005; 9,575,037; 9,603,775; 9,603,780; 9,608,228; 9,614,160; 9,625,764; 9,655,293; 9,663,400; 9,668,944; 9,682,019; 9,688,540; 9,700,485; 9,700,486; 9,705,099; 9,707,153; 9,707,154; 9,707,155; 9,713,572; 9,717,648; 9,717,649; 9,745,223; 9,755,191; 9,765,167; 9,768,026; 9,790,124; 9,839,579; 9,849,066; 9,871,209; 9,905,516; 9,915,756; 9,917,263; 9,923,000; 9,923,166; 9,972,802; 9,991,293; 9,991,453; 9,993,395; 9,999,576; 20010021292; 20010039810; 20010043996; 20020025493; 20020031731; 20020041137; 20020066233; 20020092325; 20020108400; 20020160685; 20020173416; 20030003474; 20030009126; 20030039459; 20030070916; 20030109202; 20030113506; 20030128428; 20030203205; 20040016769; 20040023087; 20040154488; 20040161789; 20040192063; 20040192171; 20040209756; 20040221515; 20040242792; 20050048571; 20050054510; 20050056806; 20050069640; 20050147752; 20050227148; 20050233886; 20060119249; 20060141362; 20060147369; 20060160919; 20060226421; 20060227695; 20060235060; 20070029927; 20070048531; 20070189986; 20070214467; 20070259220; 20080015494; 20080026220; 20080047599; 20080057267; 20080087629; 20080106261; 20080110491; 20080139342; 20080145707; 20080233434; 20080268618; 20080280424; 20080284719; 20080284768; 20080290329; 20080290795; 20080302418; 20080306182; 20080308792; 20090004764; 20090004878; 20090011575; 20090014055; 20090043116; 20090075083; 20090076189; 20090098674; 20090117707; 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[0136] Alternately, the process can for a mechanically prestressed layer, which does not rely solely on ion exchange chemical hardening to define the mechanical properties of the glass. Further, the deposition according to the present technology may be regionally controlled in the plane of the substrate, and also controlled in depth based on processing parameters and/or use of multiple layers which may be the same or different. The layers or patterns may advantageously provide distinct properties, such as electrical conductivity and conductive channels or planes, optical properties, and the like.

[0171] The present technology provides a method for bonding metal powder to various types of dissimilar substrates, employing process technology that forms an adhesion layer from components of the substrate and the metal powder, substantially without causing heat damage to nearby or underlying structures.

[0172] Metal powder may be deposited in fused layers a non-metal substrate by directed-energy powder fusion manufacturing. The energy source for this process can be from any focused energy sources, and popular sources include laser and electron beams. The powder can be deposited uniformly over an entire layer and then selectively melted, as is done in powder bed fusion processes, or it can be made with powder that is directly deposited onto the area of the part that is being exposed to the focused energy source, in the process typically referred to as directed energy deposition. The directed energy source may be steered or the sample stage may move the sample to selectively fuse powder where desired. This process is conducted in an inert environment, such as an Argon, N₂, or vacuum environment to reduce oxidation risk.

[0173] A prototype of the technology employs a laser-powder bed fusion EOS M290 machine that possesses a 500 W peak 1064 nm Yb-fiber laser and high speed galvanometer mirror system (maximum raster speed of 7000 mm/s), which presents results which are broadly applicable to other powder bed fusion and directed energy deposition tools, regardless of the focused energy source.

[0174] This technique can involve selective melting to a high density solid, or selective sintering to a porous solid depending on the processing parameters. Differences in the processing parameters (powder deposition mechanism, powder composition, substrate properties, energy source (e.g., wavelength of laser), energy source diameter) results in changes in the acceptable range of energy delivery parameters, though the methodology to identify near-ideal processing conditions will be unchanged.

[0175] One benefit of this technology is that it enables localized high temperature bonding without damaging the sensitive circuits on the other side of the electronic wafer or sample. Even with the high temperatures of laser melting, the short exposure time of the laser limits the thermal penetration depth to avoid exceeding thermal limits of nearby elements. The thermally effected zone is quite small, as the exposure time for typical focused energy powder fusion is only ˜100 μs. The zone that is thermally affected can be estimated by the thermal penetration depth, L_p ∝ √{square root over (αt)}. [64] This depth is less than the typical electronic wafer thickness (e.g., 300 μm for silicon), and so can be safely performed without damaging sensitive devices. This short exposure also enables building of higher melting temperature metals onto low-melting point alloys (e.g., stainless steel 316L on Sn₃Ag₄Ti on Si or graphite).

[0176] In particular, during selective laser melting, the metals are typically only molten for times on the order of 75 μs (assuming typical scan rates of 1 m/s, and focused energy spot sizes of 75 μm). This period is much shorter than the typical time for conventional bonding of dissimilar materials (tens of milliseconds to tens of minutes). To overcome this kinetic limitation, the focused energy locally heats the sample beyond the melting point to thermally overcome the energy barrier for the active metal species to more easily diffuse, as the diffusivity, D, has an Arrhenius rate term so that the D ∝ exp(−E_a,D/K_B T), where E_a,D is the energy barrier for the active alloy element to diffuse. The barrier to nucleate intermetallic phases can also be overcome faster at higher temperature, as the nucleation rate, N, will also be N ∝ exp(−E_a,N/K_B T), where E_a,N is the energy barrier for intermetallic phases to nucleate at the interface.

[0177] The contact angle and mechanical strength of the interface is not at its highest after a single exposure. Therefore, another key insight provides exposure of a single layer of brazing alloy to energy pulses multiple times. This provides greater time for diffusion of the active metal species and nucleation of the intermetallic phase. The benefit of a greater number of exposure diminishes with each successive exposure. For Sn₃Ag₄Ti on silicon and graphite, the difference between single and double exposures is extreme, but negligible additional improvements for three and more exposures.

[0178] FIG. 1 shows an overview of this embodiment of the additive manufacturing process.

[0179] Additive manufacturing on electronic substrates can be performed at the wafer level, after dicing, or after reflow onto a polymeric substrate (heterogeneously integrated circuits). The wafer or chips can be mounted in a chuck that maintains the device steady by such means as a vacuum chuck or heat release adhesive. The powder can be kept away from areas where powder ingress is undesired by a powder skirt. The powder skirt can be made out of silicone or elastomeric material. The bonding can be performed on an unpolished side or polished side of the wafer. It can also be used to bond onto diamond films that are used for heat spreading. For bonding, roughening is advantageous for mechanical bonding. This same technique can also be used to make electrical contacts on electronic devices like microprocessors and power electronic devices.

[0180] Another embodiment uses this same technique to bond dissimilar metals for composite applications. The alloy may be printed directly on the metal substrate, and then the printed alloy is then bonded this metal substrate by heating to an elevated temperature, which for Sn₃Ag₄Ti is ˜220° C. This embodiment can bond to carbon materials, like graphite, that are of interest for composites, nuclear, heat transfer and medical applications. For instance, it can be used to make a pyrolytic graphite based heat spreader or heat sink. The benefit of making in pyrolytic graphite stems from pyrolytic graphite's high thermal conductivity.

[0181] Another embodiment uses a bonding alloy for one or more layers and then transitions to printing a different metal. This can be desirable when different properties of a different metal are desired. For instance, copper or aluminum may be preferred to the bonding alloy for their transport properties. For Sn containing braze will form Cu—Sn intermetallics (Cu₃Sn and Cu₆Sn₅)[65] and a braze with Ti element can bond to Al via formation of Al₃Ti intermetallics.[21]

[0182] Another embodiment uses this alloy to bond to metal as a thermally removable support material. This can help save the cost of refinishing build platforms that are currently used to build metal additively formed parts. This process works by printing the metal mixture or alloy, which forms high melting point intermetallics on the substrate, but the bulk metal melts at temperatures lower than the metal used to form the part. This bonding metal can then be used to bond to the part metal. The bonding metal can also be used as removable support internal to the part, like an overhang feature in the part. The low-melt alloy can be softened or melted in an oven.

[0183] Subsequent sub-sections detail the particular embodiment of heterogeneous Sn₃Ag₄Ti powder bonding to silicon and graphite substrates. These subsections also detail subsequent bonding of this Sn₃Ag₄Ti alloy to stainless steel (316L). This same approach and material can also bond to SiC, SiN by forming silicides, and diamond and graphite by forming carbides, and GaN, GaAs, βGa₂O₃ by forming Ga—Ti intermetallic compounds, and to silicon containing oxides of crystalline and non-crystalline types (e.g., silica glass, quartz, borosilicate glass, lithium aluminum silicates) via the formation of oxides at the interface.

[0184] In an alternative embodiment, this braze can alternatively replace the Ti with other elements that react actively with the substrate, such as Ta, Zr, V, Hf, Cr, Mo, W. The purpose of the Sn₃Ag part of the alloy is to lower the melting point and increase the activity of the active metal elements.

[0185] One embodiment of this invention uses Sn₃Ag₄Ti that reacts to form a Titanium Silicide on Si that promotes good bonding, and has a melting point around 250° C. This low melting point increases the activity of Ti. The low melting point also reduces the thermal stresses experienced on cool down from the molten state, hence preventing interfacial mechanical failure when printed. The interfacial mechanical failure is observed to be dependent on the size of the feature made and on the shape of the edges, as sharp corners are prone to greater thermal stresses.

[0186] Bonding to Silicon with Sn₃Ag₄Ti:

[0187] All experiments were conducted using a laser-powder bed fusion EOS M290 tool having a 500 W 1064 nm Yb-fiber laser and high speed galvanometer mirror system (maximum raster speed of 7000 mm/s). The machine has a N₂ generator that maintains an N₂ gas atmosphere with O₂ concentrations of less than 1.5%. A special wafer tray is used to securely hold the silicon wafer.

[0188] A Sn₃Ag₄Ti powder mixture is used as the bonding metal mixture, as it provides good bonding with Si via the Ti silicide formation, and also bonds to a broad range of other materials including graphite, Al, Cu, and Fe-based metals. This low melting point of this alloy (˜250° C.) reduces the thermal stresses experienced after solidification upon cooling. Sn, Ag, and Ti powders (>99% purity) with respective average diameters of 40 μm, 5 μm, 10 μm were mixed with weight percentages of 93%, 3%, and 4% (Sn_87.55Ag_3.11Ti_9.34) (FIG. 2). Smaller powder sizes were chosen for the lower concentration metals to facilitate mixing and reduce diffusional resistance of the Ag and Ti in the Sn melt. FIG. 2 shows an SEM image (8.6 mm WD, 9 KV EHT, SE2 detector) of mixed Ag (3 wt %), Ti (4 wt %) and Sn (93 wt %) powders.

[0189] The process parameters for the first layer of bonding and subsequent layers were determined via conventional process mapping techniques [66-71]. The process parameters were identified in a high-throughput manner, where various powers ranging from 30 to 200 watts and scanning rates from 800 to 6500 mm/s with fixed hatch distance of 0.09 mm were printed in each build, to identify the exposure parameters that provide the best wetting and bonding strength between silicon and the alloy. At the extremes, it was observed that at a fixed scanning speed, low power will result in partial sintering behavior and high power causes high vapor flux and large recoil pressure which leads to splattering. One key difference with conventional processing is that the transformation is assisted by multiple laser exposers for each layer.

[0190] FIGS. 3A and 3B show SEM images (8.5 mm WD, 18 kV EHT, SE2 detector) of two samples at the interface of alloy and silicon with different exposure parameters. FIG. 3A shows partial melting, as opposed to FIG. 3B that shows complete melting and solidification. Sample 2 possesses an average composition as expected from the mixing weights, indicating sufficient mixing (FIG. 4) as quantified by electron dispersive spectroscopy (EDS). The properties used for the sample of FIG. 3B were close to ideal.

TABLE 1
		Scan		Hatch	Layer	Energy
	Power	speed		distance	thickness	density
Sample	[W]	[mm/s]	Exposure	[mm]	[μm]	[J/mm3]
1	150	5250	Double	0.09	20	15.87
2	120	1700	Double	0.09	20	39.21

	TABLE 2
	Element	Wt % - EDS	At % - EDS
	Sn	91.13 (L shell)	83.14 (L shell)
	Ti	6.33 (K shell)	14.30 (K shell)
	Ag	2.55 (L shell)	2.56 (L shell)

[0191] FIG. 4 shows quantitative measurement of elemental composition of alloy using EDS (DT between 30% to 40%). SEM image (8.2 mm WD, 15 kV EHT, SE2 detector). The specimen was polished up to 20 nm roughness.

[0192] This alloy-silicon bond can survive subsequent printing of high temperature metals, like stainless steel 316L (melting point≈1400° C.). The Sn₃Ag₄Ti alloy forms an interlayer between silicon and the stainless steel that wets and bonds to both. A good bond was achieved by depositing three layers the alloy and from then on printing the stainless steel. Parts produced by this method are shown in FIGS. 5A and 5B, which show Sn₃Ag₄Ti alloy deposited on silicon by SLM process. FIG. 5C Stainless steel Binghamton University logo built on 4″ silicon wafer. 316L was selected because it demonstrates the temperature survivability. For heat transfer applications, high thermal conductivity metals, like Al and Cu can be used instead [72]. The choice of 316L stainless steel is to demonstrate robustness to hotter melting temperatures.

[0193] The reliability of the bond to thermal cycling was probed via thermal cycling. The Si—Sn₃Ag₄Ti-SS316L samples were thermal cycled in Thermotron chamber between −40° C. and 130° C. for 100 cycles (over 1 week of testing). The temperatures of the parts are monitored to confirm the parts reach the chamber setpoints each cycle. After the 100 cycles, the parts were visually examined for defects, such as delamination, along the perimeter where thermal stresses are greatest. All parts passed the visual test without any noticeable failure or defect. FIG. 1 shows stainless steel parts fabricated by SLM on silicon wafer after thermal cycling test (100 cycles from −40° C. to 130° C.). (Note, the steel plate used to secure the silicon to the build platform has rusted over the course of the thermal cycling.)

[0194] Characterization of Si-Alloy Interface

[0195] FIG. 2 shows a sample with different patterns printed under varying conditions. Surface property and mechanical strength were studied versus processing parameters, including number of exposures. Silicon is held in a wafer holder. Wafer can be held by a vacuum chuck or adhesive and the chuck can include powder skirts to prevent powder ingress into undesired areas The strength of the Sn₃Ag₄Ti—Si bond was destructive shear tested with a Nordson DAGE 4000 Plus on hemispherical balls with a mean diameter of 432. μm. The stylus is positioned 1 μm from the interface with top raster speed of 100 μm/s. During the test it is observed that the balls did not fracture at the interface and rather scraped from the alloy. This indicates that the bond at the interface is stronger than the shear strength of the alloy.

[0196] FIG. 8 shows the bond strength of the Sn₃Ag₄Ti-silicon fabricated by SLM technique (laser power 120 W, laser scan velocity 1100-2300 mm/s, double exposure). Consequently, what is being reported in FIG. 8 is the lower limit of the interfacial strength. The obtained data show shear strengths between 14.7 to 22.1 MPa. This value was expected as shear strength of pure Sn is 17.7 MPa and Sn-3.5 Ag is 31.7 MPa [73]. Each sample is repeated ten times with standard deviation of ˜10%. A control test on the silicon wafer was also performed with 0 μm liftoff, and the frictional force was negligible compared to the force due to the alloy. The slower laser scan velocities have higher lower limits of the interfacial strength, indicating stronger alloy at these processing conditions. Balls fabricated by single exposure generally obtained lower interfacial strength compared to double exposure.

[0197] The solidified metal contact angle is a proxy for the interfacial bonding strength between the alloy and the silicon substrate. Better wetting implies a lower energy interface and stronger interfacial bonding [19]. In lieu of instantaneous contact angle measurements during selective laser melting, the contact angles of a solidified metal lines are studied (FIGS. 9A-9D) [74, 75]. While the system is not in equilibrium during the transient cooling, the contact angle still provides insight and approximates the liquid contact angle [19]. The exposure parameters were varied, by varying scan rate from 1500 mm/s to 2300 mm/s while holding power at 120 W. Each solidified metal line was formed at a different laser exposure ranging from 1500 mm/s to 2300 mm/s and power of 120 watts. Afterwards the contact angles of each line were studied by optical profilometry and the height-to-diameter (H/D) ratio is used to extract the contact angle [19], θ_equiv=2 a tan(2 H/D). By lowering the velocity of scan, the laser heating period and maximum temperature increases, which improves the diffusion of reactants, assisting spreading. FIGS. 9A and 9B show examples of optical profilometry for a line of alloy on silicon created by 120 W, 1500 mm/s exposure parameter. FIGS. 9C and 9D show equivalent contact angle measurement versus laser scan velocity based on optical profilometry.

[0198] Based on the Si—Ti phase diagram, it is expected to observe titanium-silicides at the interface as they are energetically favored [76, 77]. The growth and formation of the titanium silicide rapidly forms over the limited molten metal phase and is limited by diffusion of Ti. Hence, a very thin silicide forms just at the interface. This is visible form the electron dispersive spectroscopy (EDS) mapping of the interface. The concentration of Ti is seen to have a bright line near the interface, as pointed out in FIG. 10F. This titanium-silicide band appears about 1 μm wide, but this is an artifact of the EDS interaction volume being on the order of a 1 μm³ [78]. The actual titanium-silicide layer formed in this process is sub-μm. Noteworthy, the laser-processed silicide thickness and EDS maps are comparable to conventional brazing to silicon [18].

[0199] FIG. 10A shows a representative EDS spectrum of the alloy-silicon interface (8.7 mm WD, 10 kV EHT, DT 20%). FIG. 10B shows a back scatter detector scanning electron microscopy image of the interface shows light elements (i.e., Ti) darker than heavy elements (i.e., Sn, Ag) (8.7 mm WD, 10 kV EHT, RBSD detector). FIG. 10C shows EDS mapping of the SiK peak. FIG. 10D shows EDS mapping of the, AgL peak. FIG. 10E shows EDS mapping of the SnL peak. FIG. 10F shows EDS mapping of the TiK peak. The scalebar is 1 μm.

[0200] The energy barrier for diffusion and crystallization must be overcome with thermal energy, so the reaction rate is expected to have an Arrhenius rate equation, exp(−E_a/k_B T), where N is the nucleation rate, E_a is the activation energy, k_B is the Boltzmann constant, and T is absolute temperature [62]. Due to the rapid laser processing temperature, diffusion and nucleation can overcome the energy barrier more rapidly than conventional brazing and proceed more rapidly than reactions occurring just above the melting point of the metal, which explains why the bonding is rapid. Despite faster reaction rates, the rapid cooling rates are on the order of millions of degrees Celsius per second, which leads to quenching and non-equilibrium properties.

[0201] Properties of the Alloy on Si

[0202] On the test designed for surface and interface properties, six rectangles were created with exposure parameters similar to sample 2 in terms of hatch distance, power and scan speed but with single, double and triple exposures (FIGS. 11A, 11B, and 11C). Surface optical profilometry reviled improvement on surface roughness from first to second exposure. However, the third exposure did not improve the surface properties any further. FIGS. 11A-11C show a surface roughness study by optical profilometry on three samples with different number of rasters (120 W, 1700 mm/s, 0.09 hatch distance).

[0203] Grazing incidence X-ray diffraction (GIXRD) was performed on a bulk Sn₃Ag₄Ti sample to identify the compounds that appear in the laser processed alloy, and compare them to the conventionally processed braze. See FIG. 12, which shows phase identification of Sn—Ti—Ag alloy fabricated by SLM process using GIXRD (PANalytical X'Pert PRO High-Resolution X-ray Diffractometer). The dominant signal is from the β-Sn phase, as expected from the large concentration of Sn in the alloy. There are also weak, yet distinct peaks from the intermetallic compounds Sn₅Ti₆ and Ag₃Sn. These formations agree with what is thermodynamically expected from phase diagrams [79, 80]. Moreover, this agrees with prior conventionally processed Sn₃Ag₄Ti alloy phases, showing that laser processing and conventional brazing results in similar phases being formed [18, 21].

[0204] Bonding to Graphite with Sn₃Ag₄Ti:

[0205] One of the key challenges in additively manufacturing metal parts is removing the printed part from build platform. Conventional platforms are made of the same material as the metal powder to achieve reliable bonding and resistance to thermal stress. Support or solid structures are used to provide required offset for the cutting blade to detach the part from building platform followed by detailed machining to achieve proper surface finish. This process adds additional machining, particularly challenging for difficult to machine metals, like titanium or stainless steel. Another downside of the current build plate paradigm is that current building platforms used in commercial metal printing devices are heavy. These blocks need to be removed each time the process completes. Since graphite is lightweight, graphite buildplates can help to make handling and post-machining easier and safer.

[0206] The graphite crystal structure consists of strong Graphene planes (sp² hybridization of carbon atoms) which are connected by π-orbitals resulting in weaker interplanar Van der Waals forces [81, 82]. The thermal conductivity in the graphene plane is extraordinary (>1700 W/m-K) over eight times better than aluminum. Furthermore, graphite is 16% lighter than aluminum. Graphite also possesses beneficial properties for nuclear applications. The thermal conductivity of pyrolytic graphite makes it an attractive material for use as a heat spreader, especially when coupled with a heat pipe or heat exchanger that is additively printed.

[0207] Studying wetting of metal alloys on substrates of dissimilar material can provide valuable insights regarding bonding. However, there are debates regarding the mechanism of wetting in metal alloy systems at high temperatures. In non-reactive systems, it is hypothesized that wetting occurs by displacement of molecules of advancing front on adsorption sites of the substrate originated from surface tension. Interdiffusion and dissolution of the substrate directly affects the composition of the liquid and as a result solid-liquid interfacial energy [9]. For reactive systems, wetting is limited by the diffusion of reactive elements and local reaction kinetics [10].

[0208] The joining of dissimilar materials such as graphite to common metals employed in additive manufacturing is challenging due to these metals having contact angles greater than 130° (i.e., non-wetting) [81]. Reactive metals like Ti, Ta, Zr, and Nb have been bonded to graphite by employing carbides of the same metal as an interlayer. This process is done in furnace at temperatures around 1000° C. for 90 minutes [83]. The reason for wetting behavior is carbide formation at the interface by diffusive transport of reactive species which result in modification of specific surface energies of the system [81]. The bonding time in these conventional bonding techniques is very long (minutes to hours), compared to laser exposure time in additive manufacturing (˜100 μs).

[0209] Previously, rods of Graphite and SUS304 Stainless Steel were joined using solid state diffusion bonding method under compressive pressure of 25 MPa, annealing temperature of 664° C. and duration of 120 minutes. Clearly, this methodology is not applicable in the present method as basic requirements such as annealing time and pressure cannot be satisfied [23]. In another study, brazed carbon-carbon composite was brazed to Stainless Steel 316L at a temperature of 1050° C. using BNi-7 (Ni-14Cr-10.5P-0.1Si) filler alloy. Observation of the microstructure confirmed the carbide formation. Joint shear strength of approximately 16 MPa reported at 1 mm thickness of Nb interlayer [24]. Sn—Ag—Ti alloys are considered as “active” alloys which makes them suitable candidate for bonding of metals to various materials such as ceramics and carbon materials at temperatures between 250° C. to 450° C. [15] Activity of elements under required thermodynamic condition is of interest as it influences the effectiveness of the bond between alloy and substrate. Based on a thermodynamics study on Sn—Ag—Ti filler alloys, the activity of Ti increases with weight percentage between 0 and 2.25 wt % at 450° C. The addition of silver at low mass fractions (e.g., 3 wt %) tends to increase the titanium activity at 450° C.[59]

[0210] The contact angle of Sn—Ti and Ag—Ti alloys on graphite was reduced to under 10° by adding approximately 2-5 wt % of titanium to the systems. As a result, it is expected to see acceptable wetting on graphite. Also in the case of using the alloy as interlayer to bond steel to graphite, the reactive wetting mechanism of Sn/Fe system can is described by dissolution of Fe and precipitation of FeSn₂ at the interface [25]. Similarly, intermetallics form with this alloy and Cu (e.g., Cu₃Sn, Cu₆Sn₅). Sn is also known to wet aluminum at 350-450° C.[25]

[0211] Superfine isomolded graphite with grade of GM-10 was purchased from Graphitestore.com and machined into samples 1″×1″×0.125″ to fit experimental configuration. Similar performance can also be achieved on higher quality pyrolytic graphite with slightly adjusted processing parameters. Building on pyrolytic graphite may be desired for certain applications that demand high thermal conductivity and excellent heat spreading, as the in-plane thermal conductivity exceeding 1,700 W/m-K [84].

[0212] As initial test, stainless steel 316L was deposited on the graphite surface by various exposure parameters. The idea was that 316L steel has minimum 17 percent chromium content which might assist the bond by creating carbides at the interface [85]. The results indicated poor wetting in all tests, as shown in FIG. 13A, which presents an optical image of stainless steel 316L deposited on graphite exhibiting poor wetting. The fixture designed to hold graphite substrate on build platform of EOS M290 is shown in FIG. 13B.

[0213] As mentioned above, various elements are investigated to find a metal or alloy that can produce proper bond with carbon materials which can be applied in additive manufacturing. Sn—Ti—Ag alloy is chosen next as it provides good bonding between broad range of materials including carbon, aluminum and iron based metals in conventional brazing. Silver, titanium and tin powders with respective average diameters of 5 μm, 10 μm and 40 μm and purities of above 99% were mixed. Working with various diameter of powders show that size distribution has great importance in homogeneity and quality of uniform deposition on substrate.

[0214] The exposure power was set to 200 watts and a scan rate of 1000 mm/s was used to ablate a rectangular volume at the interface of two graphite pieces with RMS depth of 29.83 μm (measured by Veeco NT1100 optical profilometer). Three-dimensional Topography of the surface at the edge of exposed area to laser scan can be seen in FIG. 14, which shows optical profilometry of ablated graphite. The area scan size is 1.7×2.3 mm. Laser ablation was used to create a roughened surface for better adhesion, and to expose clean graphite surface. Also, for wetting liquids, increases in surface roughness can improve wetting behavior [86]. This step could possibly be omitted, though with weaker bonding.

[0215] Phase transformation and reactive wetting are dictated by laser matter interactions, transport and reactions during this process. Various powers ranging from 30 to 200 watts and scanning rates from 800 to 6500 mm/s and constant hatch distance of 0.09 mm were tested to find the exposure parameters that provide the highest wetting and bonding strength between graphite and the alloy. During this process, it is observed that at a fixed scanning speed, low power will result in partial sintering behavior and high power causes high vapor flux and large recoil pressure which leads to splattering. These process parameter trends with scan rate and power mostly agree with the general process parameters seen for other materials [61]. One key difference with regular stainless steel processing is that the mixed powder phase transformation is assisted by a double laser exposing each layer. The bonding appears to be a two-step process that requires a double exposure

[0216] In an experiment, three layers of the alloy with thickness of 40 um each are deposited on graphite surface by laser melting. Afterwards, two layers of powder mixed with 50 wt % of stainless steel 316L deposited with same exposure parameters on the surface to create an elemental gradient in the build normal direction. Afterwards, a “Binghamton University” logo was built on the alloy with SS316L material using support structure exposure parameters to study the applicability of the interlayer method. Since the alloy meting temperature is under 450° C., the graphite with the structure built on it then removed from the build platform and placed on a hot plate. By increasing the temperature of the hot plate to 400° C. for one minute, the part can be separated from the graphite substrate. FIG. 15A shows the stainless steel logo printed on graphite. FIG. 15B shows removal of the printed part using hot plate.

[0217] A sessile drop experiment is generally used for molten metal contact angle measurements. However, it is hard to accurately study instantaneous spreading process in case of selective laser melting, as phase change occurs fast. On the other hand, solidified sessile drop measurements can be used to give an estimate on the contact angle. However, since in SLM the molten metal drop solidifies before reaching its equilibrium state [74, 75]. The contact angle can be estimated from the solidified droplet shape [87]. Studying the post-solidified triple contact line can in various exposure parameter provides information regarding the wetting mechanism during laser processing. Based on this ideology, an experiment is designed to create 5 lines of 120 μm width on graphite. Each line was scanned by a different laser exposure ranging from 5000 mm/s to 6000 mm/s and power of 150 watts. Afterwards the contact angles of each line are studied by optical profilometry. FIGS. 16A and 16B show spreading of the alloy on graphite substrate based on laser exposure parameters. The height-to-width (H/D) ratio is provided for each scanned line in order to have a better comparison. By lowering the velocity of scan, the laser heating period and maximum temperature increase, which improves the diffusion of reactants, assisting spreading.

[0218] The energy barrier for crystallization must be overcome with thermal energy, so the reaction rate is expected to have an Arrhenius rate equation, N ∝ exp(−E_a/k_BT), where N is the nucleation rate, E_a is the activation energy, k_B is the Boltzmann constant, and T is absolute temperature [62]. Due to the rapid laser processing temperature, nucleation can overcome the energy barrier and proceed more rapidly than reactions just above the melting point of the metal, which explains why bonding occurs so rapidly. Despite faster reaction rates, the rapid cooling rates are on the order of millions of degrees Celsius per second, which leads to imperfect quenching of the interfacial layer with defects with respect to microstructure and surface coverage due to reaction and diffusion kinetics.

[0219] Since the bond is under combined normal and shear stresses imposed by the thermal stress inherent to SLM and the recoating blade of SLM machine, it is necessary to measure the bonding strength of the joint. The common approach is to perform tensile tests to calculate yield tensile strength and shear yield strength of the joint. However, these tests are designed for isotropic or homogenous materials, which are not the case at the interface [88, 89]. Direct measurement of tensile load at the joint is not straight forward since there is not enough space to grip the deposited layer of metal. To characterize the joint, a lap shear test according to FIG. 17 is performed, where the alloy layer functions as a weld connecting two graphite blocks that are loaded under tensile load.

[0220] The designed mechanical testing reveals the lower limit of interfacial strength for the alloy in FIGS. 18A, 18B and 18C, which shows the Interfacial strength of the graphite-metal bonding at various laser scan velocities (FIGS. 18A and 18B). Sample preparation for tensile test (FIG. 18C). Since the fracture occurred in alloy for most of the samples rather than at the graphite-metal interface, only a lower limit of the interfacial strength can be estimated (shown by arrow).

[0221] FIG. 19 shows an optical image using a polarized light microscope of the Sn—Ag—Ti alloy laser bonded onto graphite.

[0222] FIG. 20 shows an unpolished scanning electron microscopy of graphite-alloy interface.

[0223] Similar processing will work for printing onto pyrolytic graphite. FIG. 23 shows a print on a pyrolytic graphite sample. Pyroid® HT pyrolytic graphite substrate is thermally annealed in the manufacturing process to increase its thermal conductivity up to 1700 W/m-K at room temperature. Owing to the higher thermal conductivity of pyrolytic graphite, a greater energy density is required for bonding. This sample was made at laser scan speeds ranging from 4400 mm/s to 5600 mm/s and 150 W power and 20 μm layer thickness. Double exposure was applied to all samples. Ball shear testing is performed to measure interfacial strength of Sn₃Ag₄Ti alloy deposited by different laser processing parameters on pyrolytic graphite as shown on FIG. 24. 4400 mm/s and 150 W process parameters provided highest bond strength.

[0224] Energy-dispersive X-ray spectroscopy (EDS)/SEM 15 kV MAG 300 performed on the interface of the joint is shown in FIGS. 21A and 21B. A scan across the interface shows diffusion of Carbon into the alloy. Elemental compositions observed at the interface show a titanium-tin-carbide interlayer [90]. Carbide formation is observed near the interface between graphite (bottom) and alloy (top).

	TABLE 3
	Element	C	Ag	Sn	Ti
	At %	25.85	00.00	61.92	12.22
	Wt %	03.77	00.00	89.13	07.10

[0225] To examine the reliability of the bond in various thermal conditions, a thermal cycling test is performed. The bulk SS316L samples printed on graphite were tested using a Thermotron temperature chamber. During the test, the chamber temperature varied from −40° C. to 130° C. for 100 cycles. The temperatures of the parts are monitored. After the 100 cycles (over 1 week of testing), the parts were visually examined for defects, such as delamination, along the perimeter where thermal stresses are greatest. All parts passed the visual test without any noticeable failure or defects. FIGS. 22A and 22B show two stainless steel parts after the thermal cycling test.

[0226] This technology efficiently and effectively employs a focused energy additive manufacturing process capable of bonding metals onto to graphite. Parts produced by this method can help effectively spread heat and take advantage of the high in-plane thermal conductivity of pyrolytic graphite. Furthermore, graphite can be used as an alternative build platform which decreases the cost of printing with stainless steel or titanium since current metal additively manufactured parts require machining to remove support, which requires either manually machining the parts or computer-controlled machining (CNC), which are both expensive and time-consuming. There is no need to print support structures as the part can be printed directly on the build platform and separated from it after print by melting the alloy connecting the stainless to graphite, or by brittle fracturing the graphite plate.

[0227] Detailed Bonding to Silica-Based Compounds with Sn₃Ag₄Ti

[0228] Experiments were conducted using a laser-powder bed fusion EOS M290 tool having a 500 W 1064 nm Yb-fiber laser and high speed galvanometer mirror system (maximum raster speed of 7000 mm/s). The machine has a N₂ generator that maintains an N₂ gas atmosphere with O₂ concentrations of less than 1.5%. A special wafer tray is used to securely hold the silicon wafer.

[0229] A Sn₃Ag₄Ti powder mixture is used as the bonding metal mixture, as it provides good bonding with silica and alumina via the Ti silicide and Ti oxide formation [58, 91-93], and also bonds to a broad range of other materials including graphite, Al, Cu, and Fe-based metals. This low melting point of this alloy (˜250° C.) reduces the thermal stresses experienced after solidification upon cooling. Sn, Ag, and Ti powders (>99% purity) with respective average diameters of 40 μm, 5 μm, 10 μm were mixed with weight percentages of 93%, 3%, and 4% (Sn_87.55Ag_3.11Ti_9.34) (FIG. 2). Smaller powder sizes were chosen for the lower concentration metals to facilitate mixing and reduce diffusional resistance of the Ag and Ti in the Sn melt. FIG. 2 shows an SEM image (8.6 mm WD, 9 KV EHT, SE2 detector) of mixed Ag (3 wt %), Ti (4 wt %) and Sn (93 wt %) powders.

[0230] FIGS. 25 and 26A and 26B show optical and scanning electron microscopy images of the first layer of printing Sn₃Ag₄Ti alloy onto a borosilicate glass substrate fractured at the interface. The laser processing parameters used for this deposition are given in table 4.

TABLE 4
		Scan		Hatch	Layer	Energy
	Power	speed		distance	thickness	density
Sample	[W]	[mm/s]	Exposure	[mm]	[μm]	[J/mm3]
1	120	1700	Double	0.09	20	39.21

[0231] Energy dispersive X-ray spectroscopy mapping was applied at the interface of the sample with the Sn₃Ag₄Ti alloy deposited onto borosilicate glass to investigate the bonding, as shown in FIGS. 27A-27F. During directed energy deposition by the laser, the titanium in the alloy reacts to silica and create titanium oxide and titanium silicide. Presence of similar patterns for Ti, Si and O in EDS elemental mapping supports titanium oxides forming at the interface.

[0232] Detailed Bonding to Al₂O₃-Based Compounds with Sn₃Ag₄Ti

[0233] An EOS m290 system and Sn₃Ag₄Ti alloy powder was used to print on D50×0.43 mm Sapphire wafer with <0001> orientation and single side polish, installed on a steel build platform using Kapton tape. FIG. 28A shows the powder mounted on the build platform. The sapphire is unpolished on the side that was printed on. FIG. 28B shows a thin single layer of approximately 54 μm (the thickness of the Kapton tape) of Sn₃Ag₄Ti alloy powder, deposited on the unpolished surface with manual deposition. FIG. 28C shows the pattern of pillars and lines printed with this technique using a laser power of 150 W with scanning rate from 4400 to 5600 mm/s and a spot size of approximately 100 μm. As can be seen in the brightfield optical microscope images of FIG. 28D and FIG. 28E, good bonding can be achieved with a scan rate of 4400 mm/s and a power of 150 W. FIG. 28D shows bright field optical imaging at 5× of two lines, top with 150 W and 4400 mm/s and bottom with 150 W and 4600 mm/s. FIG. 28E shows bright field optical imaging at 20× magnification of 150 W 4400 mm/s line with Z-stack. Line thickness of 100 μm is achieved with edge exposure (single line raster).

[0234] The present technology provides an alternate technique for direct fabrication of heat transfer devices onto the chip by additive manufacturing, by building on recent hybrid bonding literature for interconnect manufacturing [98-101]. Previously lead solders, and more recently non-lead solders, have been used extensively in the electronic packaging industry to form interconnects, etc. However, reliability concerns are pushing the industry to move away from solders, towards a concept called hybrid bonding [94-97] which does not require solders. Hybrid bonding consists of multi-stage physical and chemical depositions onto a semiconductor device by employing photolithography-based techniques. This process produces a thin bonding layer via depositions that can then have features, like fins and microchannels, additively deposited via a powder-based laser melting process.

[0235] In this example, ˜50 nm of titanium is deposited onto the back of the semiconductor die by physical vapor deposition (PVD), such as sputtering or evaporation as adhesion layer. This layer could be patterned or unpatterned. Then ˜250 nm of copper is deposited on top with similar techniques. Afterwards, 5-40 μm of copper layer is grown by electrodeposition onto the seed layer. This process is illustrated in FIG. 29. After metallizing the silicon with Cu, it is possible to 3d metal print heat sink structures made of copper directly on the metalized surface. Alternative embodiments may choose to make features out of other high conductivity metals, like silver or aluminum. This technique has an interface from titanium to the silicon via titanium silicides, and the first interlayer to the copper via Ti—Cu intermetallic formation.

[0236] The disclosure has been described with reference to various specific embodiments and techniques. However, many variations and modifications are possible while remaining within the scope of the disclosure.

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