Center bond flip chip semiconductor carrier and a method of making and using it

[0002] The present invention generally relates to semiconductor chip fabrication. More particularly, the present invention relates to a center bond flip chip semiconductor carrier and a method for making and using it to produce a semiconductor device.

[0003] Semiconductor device packaging techniques are well known. In some conventional packaged devices, a die is attached to a carrier, and contacts of each are electrically connected. In one such packaged device called a flip-chip device, a semiconductor chip is flipped and bonded with a carrier such that contacts of the die face and bond to contacts of the carrier.

[0004] With reference to FIGS. 1-3, a conventional center bond flip chip device 10 is shown as including a flipped die 30 and a carrier 11. The carrier 11 has a flexible substrate 12 and an elastomeric cover material 14. The elastomeric material 14 may be formed of a silicone or a silicone-modified epoxy. The elastomeric material 14 includes a first portion 15 and a second portion 17 of generally equal size. The flexible substrate 12 is formed of a material exhibiting high temperature stability as well as high mechanical rigidity. The substrate 12 may be a flexible tape, such as, for example, a polyimide tape. Two commercially available polyimide tapes, KAPTON® from E. I. DuPont Nemours and Company and UPILEX® from Ube Industries, Ltd., can be used to form the substrate 12.

[0005] Conductive traces 16_a, 166_b, 16_care formed on the flexible substrate 12 and positioned below the elastomeric material 14. The traces 16_a, 16_b, 16_cmay be deposited on the flexible substrate 12 in a variety of ways, the most preferred method being electrolytic deposition. Other suitable methods include sputter coating and laminating a sheet of conductive material and etching away excess material to form the traces.

[0006] A gap 20 separates the two portions 15, 17 of the elastomeric material 14. Conductive lands 18_a, 18_b, 18_care positioned on, respectively, the conductive traces 16_a, 16_b, 16_cwithin the gap 20. The die 30 has been removed from the FIG. 1 for clarity of illustration of the lands 18_a, 18_b, 18_c. As illustrated, the gap 20 is rectangularly shaped, although any configured gap will suffice as long as the conductive pads 18_a, 18_b, 18_care not covered by the elastomeric material 14.

[0007] A die 30 is positioned on the elastomeric material 14 of the carrier 11. The carrier 11 is electrically connected with the die 30 by way of suitable conductive connecting structures, such as, for example, inner lead solder balls or bumps 19_a, 19_b, 19_cpositioned on, respectively, the conductive pads or lands 18_a, 18_b, 18_c. Conductive vias 22_a, 22_b, 22_crespectively extend from each of the underside surfaces of the traces 16_a, 16_b, 16_c. Outer lead solder balls or bumps 24_a, 24_b, 24_c, or other conductive connecting structures, are located in electrical connection with each respective via 22_a, 22_b, 22_cand serve to connect the traces 16_a, 16_b, 16_cto a structure or common base for mounting components, such as, for example, a printed circuit board 35. Preferably, the outer lead balls 24_a, 24_b, 24_care about 16 mils in diameter.

[0008] Conventional center bond flip chip semiconductor devices have several disadvantages, particularly as die 30 sizes decrease and the contacts thereof are positioned closer together. One disadvantage is that adjacent traces 16_a, 16_b, 16_cof the carrier 11 and their associated conductive lands 18_a, 18_b, 18_cmust likewise be positioned closer together to such an extent that the inner lead balls 19_a, 19_b, 19_cwill occasionally contact one another, thereby shorting out the semiconductor device. Another disadvantage is that in positioning the inner lead balls 19_a, 19_b, 19_con the conductive lands 18_a, 18_b, 18_c, wicking of the solder balls onto the conductive traces may sometimes occur during the solder process, providing less of a solder ball surface to make good electrical contact between the die 30 bond pad and a conductive land 18 of the carrier 11.

[0009] There is, therefore, a need for a center bond flip chip semiconductor device design which alleviates to some extent these disadvantages.

[0010] The present invention provides a carrier for a semiconductor device which includes a substrate, at least one conductive trace located on the substrate, the trace including a recessed seat sized and configured to receive a conductive connecting structure, for example, a solder ball, and an elastomeric covering material, the material including a gap in which the conductive connecting structure may be located in the recessed seat to provide a reliable electrical connection of the trace with a flipped semiconductor die.

[0011] The present invention further provides a semiconductor device including a semiconductor die electrically connected to a carrier. The carrier includes at least one conductive trace located on a substrate. The trace includes a recessed seat sized and configured to receive a conductive connecting structure to allow electrical connection of the trace with the semiconductor die.

[0012] The present invention further provides an electronic system which includes a semiconductor die, a carrier and a structure for mounting the carrier. The carrier has a substrate, a plurality of conductive traces located on the substrate, and an elastomeric covering material. Each trace includes a recessed seat having a cut out portion sized and configured to receive a conductive connecting structure. The elastomeric material includes a gap corresponding to the location of the recessed seats to allow electrical connection of the traces with the semiconductor die.

[0013] The present invention further provides a method for making a carrier for a semiconductor die. The method includes locating at least one conductive trace on a substrate, and creating a recessed seated portion on the trace, which recessed seated portion can be used to seat a conductive connecting structure used for interconnecting the carrier to a semiconductor die.

[0014] The present invention further provides a method of making a semiconductor device. The method includes forming a carrier and electrically connecting the carrier with a semiconductor die. The forming includes locating at least one conductive trace on a substrate, creating a recessed seated portion on the trace, and affixing a conductive connecting structure which is coupled to the semiconductor die to the recessed seated portion.

[0015] The foregoing and other advantages and features of the invention will be more readily understood from the following detailed description of the invention, which is provided in connection with the accompanying drawings.

[0016] FIG. 1 is a top view of a conventional center bond flip chip carrier.

[0017] FIG. 2 is a side view of a conventional center bond flip chip semiconductor device incorporating the carrier of FIG. 1.

[0018] FIG. 3 is a cross-sectional view taken along line III—III of FIG. 2.

[0019] FIG. 4 is a top view of a carrier for a center bond flip chip semiconductor device constructed in accordance with an embodiment of the invention.

[0020] FIG. 5 is a cross-sectional view taken along line V—V of the semiconductor device of FIG. 3.

[0021] FIG. 6 is a cross-sectional view taken along line VI—VI of the semiconductor device of FIG. 3.

[0022] FIG. 7 is a cross-sectional view of another carrier for a center bond flip chip semiconductor device constructed in accordance with another embodiment of the invention.

[0023] FIG. 8 is a cross-sectional view taken along line VIII—VIII of the semiconductor device of FIG. 7.

[0024] FIG. 9 is a cross-sectional view of a carrier for a center bond flip chip semiconductor device constructed in accordance with another embodiment of the invention.

[0025] FIG. 10 is a cross-sectional view taken along line X—X of the semiconductor device of FIG. 9.

[0026] FIG. 11 illustrates a processor-based system utilizing a carrier constructed in accordance with an embodiment of the present invention.

[0027] FIG. 12 is a flow diagram of the steps in making the flip chip carrier of FIGS. 4-10 and a semiconductor device using the carrier.

[0028] FIG. 13 is a side view of a portion of a flip chip carrier constructed in accordance with another embodiment of the present invention.

[0029] FIG. 14 is a side view of a portion of a flip chip carrier constructed in accordance with another embodiment of the present invention.

[0030] Referring to FIGS. 4-6, where like numerals designate like elements, there is shown a semiconductor device 100, which includes the die 30 and a carrier 111 having the flexible substrate 12 and the elastomeric material 14 with the first and second portions 15, 17. The die 30 is not shown in FIG. 4 for clarity of illustration.

[0031] As with the device 10 in FIGS. 1-3, a gap 20 is provided in the device 100 between the two portions 15, 17 of the elastomeric material 14. Further, electrically conductive traces 116_a, 116_b, 116_care provided on the flexible substrate 12 below the elastomeric material 14. The conductive traces 116_a, 116_b, 116_cmay be included with the flexible substrate 12, or they may be provided subsequently on the substrate 12. Seats 118_a, 118_b, 118_care provided, respectively, on conductive traces 116_a, 116_b, 116_cat a position within the gap 20. The pitch (the distance between each trace 116_a, 116_b, 116_c) is in the range of about 25 to about 500 microns. Preferably, the pitch is about 150 microns. Each of the seats 118_a, 118_b, 118_cincludes, respectively, a recessed seat formed as a cut out portion 121_a, 121_b, 121_c. The cut out portions 121_a, 121_b, 121_cmay be mechanically drilled or coined (compressed), or laser drilled or ablated, or etched. Further, while the dimension of the cut out portions 121_a, 121_b, 121_care dependent upon the size of the inner lead balls 19_a, 19_b, 19_c, they will generally range between 0.005 mm²and 1.0 mm². The inner lead balls 19_a, 19_b, 19_care preferably about three to four mils in diameter.

[0032] Each of these cut out portions 121_a, 121_b, 121_cprovides a recessed seat for the inner lead balls 19_a, 19_b, 19_c. Further, each of the cut out portions 121_a, 121_b, 121_cserves as a stop to inhibit movement of the inner lead balls 19_a, 19_b, 19_ceither along or transverse to a longitudinal axis of the traces 116_a, 116_b, 116_c. In this way, the inner lead balls 19_a, 19_b, 19_care inhibited from moving transversely from the conductive traces 116_a, 116_b, 116_c, thereby lessening the likelihood that a die connected to the carrier 111 will be shorted out by contact of adjacent inner lead balls 19_a, 19_b, 19_c. In addition, the cut out portions 121_a, 121_b, 121_chelp to prevent the wicking of the inner lead balls 19_a, 19_b, 19_clongitudinally along a respective conductive trace 116_a, 116_b, 116_c.

[0033] The ends of the conductive traces 116_a, 116_b, 116_cmay not contact the seats 118_a, 118_b, 118_c. Thus, it may be necessary to coin, or compress, the seats 118_a, 118_b, 118_cto expand their outer dimensions to the extent that they touch the conductive traces 116_a, 116_b, 116_c. Instead, a surface of the seats 118_a, 118_b, 118_cmay be electroplated with one or more metal layers 125. The metal layers 125 may be formed of a material to enhance solder wetting. Preferably, the surface of the seats 118_a, 118_b, 118_care electroplated with nickel and gold to further ensure good electrical contact between the inner lead balls 19_a, 19_b, 19_cand the respective conductive traces 116_a, 116_b, 116_c. Alternatively, if it is desired to electroplate with a material which restricts solder wetting, the metal layers 125 may be formed of tin, lead, and/or palladium.

[0034] FIGS. 7-8 show a center bond flip chip semiconductor device 200 which includes the die 30 and a carrier 211 with the elastomeric material 14 and the flexible substrate 12. A plurality of recessed seats 218_a, 218_b, 218_care provided in conductive traces 216_a, 216_b, 216_c, which are provided on the substrate 12. Each of the recessed seats 218_a, 218_b, 218_cis provided in the gap 20 formed between the portion 15, 17 of the elastomeric material 14. The recessed seats 218_a, 218_b, 218_care formed by respective a cut out portions 221_a, 221_b, 221_cin which respective inner lead balls 19_a, 19_b, 19_crest. The semiconductor device 200 of FIGS. 7-8 is different from semiconductor device 100 in FIGS. 4-6 in that the cut out portions 221_a, 221_b, 221_cdo not extend through the entire depth of the conductive traces 216_a, 216_b, 216_cInstead, a portion of each conductive trace 216_a, 216_b, 216_cremains below the cut out portions 221_a, 221_b, 221_c, so there is electrical continuity along each of the traces 216_a, 216_b, 216_c.

[0035] FIGS. 9-10 show another flip chip semiconductor device 300 which includes the die 30 and a carrier 311 having the elastomeric material 14 and the flexible substrate 12. Seats 318_a, 318_b, 318_care positioned along the conductive traces as described above with reference to FIGS. 4-8, and include cut out portions 321_a, 321_b, 321_c. Inner lead balls 19_a, 19_b, 19_crest within the seats 318_a, 318_b, 318_cwhich are positioned between the elastomeric material 14 and the flexible substrate 12. The semiconductor device 300 differs from the devices 100 (FIGS. 4-6) and 200 (FIGS. 7-8) in that the cut out portions 321_a, 321_b, 321_cextend into the flexible substrate 12.

[0036] FIG. 13 shows a portion of a flip chip semiconductor device. Specifically, an outer lead ball 124_cis shown in a via 122_c. In this embodiment, the outer lead ball 124_cis sufficiently large to contact the conductive trace 16_cas well as the printed circuit board 35. Thus, electroplating of the sides of the via 122_care not necessary, as the outer lead ball 124_calone electrically connects the conductive trace 16_cwith the printed circuit board 35 itself. The via 122_cis dimensioned to receive the outer lead ball 124_c.

[0037] Alternatively, as shown in FIG. 14, the outer lead ball 24_cis positioned within a via 222_c. The via 222_cdiffers from the via 22_cin that the via 222_clacks electroplating of its sides. Instead, a conductive material 223 is positioned in the via 222_cto provide electrical contact between the outer lead ball 24_cand the conductive trace 16_c. The conductive material 223 may be formed of a conductive paste or epoxy, or instead a conductive metal such as copper.

[0038] Referring now to FIG. 11, next will be described the use of the carrier 111, 211, 311, carrying a die 30 which contains a memory circuit such as a DRAM, within a processor-based system 500. The processor-based system 500 may be a computer system, a process control system or any other system employing a processor and associated memory. The system 500 includes a central processing unit (CPU) 502, which may be a microprocessor. The CPU 502 communicates with the DRAM 512, which includes the carrier 111 (or the carrier 211 or 311) over a bus 516. The CPU 502 further communicates with one or more I/O devices 508, 510 over the bus 516. Although illustrated as a single bus, the bus 516 may be a series of buses and bridges commonly used in a processor-based system. Further components of the system 500 include a read only memory (ROM) 514 and peripheral devices such as a floppy disk drive 504, and CD ROM drive 506. The floppy disk drive 504 and CD ROM drive 506 communicate with the CPU 502 over the bus 516.

[0039] With reference to FIG. 12, next will be described a method for making the flip chip carriers 111, 211, 311 as well as a semiconductor device in which the carriers are used to mount and support a semiconductor die. Manufacture of the carriers 111, 211, 311 begins with preparation of the flexible substrate 12 at step 400. The conductive traces 116_a, 116_b, 116_c(or 216_a, 216_b, 216_cor 316_a, 316_b, 316_c) may be included with the substrate 12, or optionally, they are deposited on the substrate 12 at step 405 by way of electrolytic deposition, sputter coating, laminating a conductive material to the substrate 12 and etching away the excess, or other suitable deposition method. The cut out portions 121_a, 121_b, 121_c(or 221_a, 221_b, 221_cor 321_a, 321_b, 321_c) are created within the traces at step 410 by laser or mechanical drilling or by etching. At step 415, the elastomeric material 14 is deposited over the substrate 12 and the traces to form the carriers 111, 211, 311.

[0040] Inner lead balls 19_a, 19_b, 19_care affixed to the traces 116_a, 116_b, 116_c(or 216_a, 216_b, 216_cor 316_a, 316_b, 316_c) at the seats 118_a, 118_b, 118_c(or 218_a, 218_b, 218_cor 318_a, 318_b, 318_c) at step 420. Alternatively, the inner lead balls 19_a) 19_b, 19_cmay be affixed to the die 30. The thus formed carrier 111, 211, 311 is then electrically connected with the die 30 bond pads at step 425 by bringing the two into contact and melting the solder balls to provide a solid mechanical and electrical contact of the die to the carrier.

[0041] Users of the thus manufactured semiconductor devices 100, 200, 300 may attach and electrically connect the devices with the printed circuit board 35 or other common base for mounting of components to form an electronic system.

[0042] The present invention provides a flip chip carrier and a semiconductor device employing it which is inhibited from being shorted out by closely spaced interconnected conductors, e.g., solder balls, and which reduces the chance of solder wicking along the electrical traces.

[0043] While the invention has been described in detail in connection with the preferred embodiments known at the time, it should be readily understood that the invention is not limited to such disclosed embodiments. Rather, the invention can be modified to incorporate any number of variations, alterations, substitutions or equivalent arrangements not heretofore described, but which are commensurate with the spirit and scope of the invention. For example, while the description and illustrations depict a center bond flip chip semiconductor device, it is to be understood that the invention is not so limited. Further, while three traces have been shown and described for the carriers 111, 211, 311, in order to illustrate the invention it should be apparent that many more traces will be used in practice. Indeed, any number of traces may be included. In addition, although inner lead balls 19_a, 19_b, 19_chave been described and illustrated, other suitable types of conductive connecting structures may be employed. Accordingly, the invention is not to be seen as limited by the foregoing description, but is only limited by the scope of the appended claims.