Surface acoustic wave device

[0002] 1. Field of the Invention

[0003] The present invention relates to a surface acoustic wave device having a structure in which a surface acoustic wave element is bonded to a substrate by a face-down mounting method, and more specifically, the present invention relates to a surface acoustic wave device having an improved structure including a substrate with a surface acoustic wave element laminated thereon.

[0004] 2. Description of the Related Art

[0005] Miniaturization and low profile of a surface acoustic wave device accommodating a surface acoustic wave element has been strongly required of surface acoustic wave devices. To meet these requirements, a structure in which the surface acoustic wave element is bonded on the substrate via a bump, with a surface having an electrode for the surface acoustic wave element such as an IDT formed thereon defining a lower surface, i.e., a structure in which the surface acoustic wave element is mounted on the substrate by a so-called face-down mounting method, has been proposed.

[0006] In addition, the surface acoustic wave device accommodating the surface acoustic wave element and having an airtight or liquid-tight sealing structure has been required so as to stabilize the characteristics thereof, and so as to be less susceptible to fluctuations in the environment.

[0007] Japanese Unexamined Patent Application Publication No. 8-265096 discloses an example of the surface acoustic wave device of this type. In this example, the surface acoustic wave element is mounted on the substrate via the bump by the face-down mounting method, and, in order to seal the surface acoustic wave element, a metal cap is fixed to an upper surface of the substrate so as to surround the surface acoustic wave element. In addition, the surface acoustic wave element is bonded to the substrate also by insulating resin, and the bonding strength of the surface acoustic wave element to the substrate is increased. In order to prevent any flow casting of this insulating resin to the electrode side of the surface acoustic wave element, a guard layer is disposed on the upper surface of the substrate outside the surface acoustic wave element.

[0008] However, in the device disclosed in this Japanese patent publication, because the metal cap must be bonded to the substrate by using adhesive, etc. as described above, the number of parts is increased, and the assembly is complicated.

[0009] On the other hand, another structure has been known, in which the surface acoustic wave element is sealed in an airtight or liquid-tight manner by mounting the surface acoustic wave element on the substrate by the face-down mounting method, and sealing the surface acoustic wave element with resin except for a surface of the surface acoustic wave element having the electrode disposed thereon. In such a device, a metal cap need not be prepared separately, and an assembly process can be simplified.

[0010] FIG. 7 is a sectional view showing an example of a conventional surface acoustic wave device having a resin sealing layer. In a surface acoustic wave device 101, a surface acoustic wave element 103 is mounted on a substrate 102, and a resin sealing layer 104 is arranged so as to surround the surface acoustic wave element 103. Electrode lands 102aand 102bare disposed on an upper surface of the substrate 102. Via hole electrodes 102cand 102dare formed in the substrate 102 in a piercing manner through the substrate 102. Upper ends of the via hole electrodes 102cand 102dare connected to the electrode lands 102aand 102b. In addition, mounting electrodes 102eand 102fare disposed on a lower surface of the substrate 102 so that the surface acoustic wave device 101 is mounted on a printed circuit board, etc. A shield ring 102gis disposed on the substrate 102 so as to provide an electromagnetic shield effect.

[0011] On the other hand, a schematically shown electrode 103afor the surface acoustic wave element is disposed on a lower surface of the surface acoustic wave element 103. Bump pads 103band 103con the lower surface of the surface acoustic wave element 103 and the electrode lands 102aand 102bare connected to each other via metal bumps 105 and 106.

[0012] In the surface acoustic wave device 101, mounting electrodes 102eand 102fare disposed on the lower surface of the substrate 102. The surface acoustic wave device 101 is surface-mounted on a printed circuit board or other substrate by using the mounting electrodes 102eand 102f.

[0013] FIG. 8 is a sectional view of another example of a conventional surface acoustic wave device of this type.

[0014] In a surface acoustic wave device 111 shown in FIG. 8, unlike the surface acoustic wave device 101, a substrate with the surface acoustic wave element 103 mounted thereon is a multi-layered substrate 112. This means that the multi-layered substrate 112 has electrode lands 112aand 112bon an upper surface thereof in a manner similar to the substrate 102. Via hole electrodes 112cand 112dare formed within the multi-layered substrate 112. However, via hole electrodes 112cand 112dare formed in the multi-layered substrate 112 so that lower ends of the via hole electrodes 112cand 112dreach the position of the middle height of the substrate 112, and connected to internal electrode 112eand 112f. Via hole electrodes 112gand 112hare formed on lower surfaces of the internal electrodes 112eand 112f. The distance between the via hole electrodes 112gand 112his larger than the distance between the via hole electrodes 112aand 112b.

[0015] In addition, the via hole electrodes 112gand 112hare arranged so as to reach the lower surface of the substrate 112, and connected to mounting electrodes 112iand 112jdisposed on the lower surface thereof.

[0016] FIG. 9 is a sectional view of yet another example of a conventional surface acoustic wave device of this type. In a surface acoustic wave device 121, electrode lands 122aand 122bare disposed on an upper surface of a substrate 122, and mounting electrodes 122cand 122dare disposed on a lower surface thereof. The electrode lands 122aand 122bon the upper surface and the mounting electrodes 122cand 122don the lower surface are electrically connected to each other via the end surface electrodes 122eand 122fdisposed on the other side of the substrate 122.

[0017] In order to reduce the size and the cost of a surface acoustic wave device, it is necessary to obtain as many surface acoustic wave elements as possible from one wafer. Thus, the cutting margin when cutting individual surface acoustic wave elements out of the wafer is reduced, or the size of the surface acoustic wave elements themselves is reduced.

[0018] When the size of the surface acoustic wave elements is reduced, the distance between bump pads for bonding the surface acoustic wave elements via bumps is reduced. This means that surface bump pads 131ato 131dare disposed in a surface acoustic wave element 131 shown in FIG. 10. Electrodes for surface acoustic wave elements such as IDTs are also formed on a surface with the bump pads 131ato 131ddisposed thereon although this is not shown in FIG. 10.

[0019] It is assumed that the surface acoustic wave element 131 is square in plan view, the length of one side is a, and the distance between bump pads is c. It is assumed that the size of the surface acoustic wave element 131 is reduced to obtain a surface acoustic wave element 132 shown in FIG. 11. In this occasion, the length b of one side of the surface acoustic wave element 132 is smaller than the length a, and similarly, the distance d between the bump pads 132ato 132dis liable to be shorter than the distance c shown in FIG. 10.

[0020] As described above, if the size of the surface acoustic wave element is reduced, the distance between the bumps must be smaller when the surface acoustic wave element is bonded on the substrate via bumps by the face-down mounting method. For example, if the size of the surface acoustic wave element 101 shown in FIG. 7 is reduced, a surface acoustic wave device 141 shown in FIG. 12 is obtained, and the distance d between bumps in the surface acoustic wave device 141 must be smaller than the distance between the bumps 105 and 106 in the surface acoustic wave device 101 shown in FIG. 7. Thus, in the surface acoustic wave device 141, the distance between the mounting electrodes 102eand 102fis reduced, and a short circuit can occur during the mounting.

[0021] On the other hand, in the surface acoustic wave device 111 including the multi-layered substrate 112 shown in FIG. 8, the distance between the mounting electrodes 112eand 112fcan be sufficiently large by setting the distance between the via hole electrodes 112gand 112htherebelow to be larger than the distance between the via hole electrodes 112cand 112deven when the size of the surface acoustic wave element 103 is reduced. However, in the surface acoustic wave device 111, the mounting electrodes 112eand 112fare disposed on the lower surface of the multi-layered substrate 112, and any fillet formation in a solder-bonded portion to the printed circuit board or substrate cannot be checked. Therefore, defective mounting cannot be discovered rapidly.

[0022] On the other hand, in the surface acoustic wave device 121 shown in FIG. 9, the electrode lands 122aand 122bon an upper surface of the substrate 122 and the mounting electrodes 122cand 122don the lower surface of the substrate are electrically connected to each other by using the end surface electrodes 122eand 122f. Thus, any fillet formation at an end surface can be visually checked when the surface acoustic wave device 121 is soldered to the printed circuit board or substrate.

[0023] However, since the electrode lands 122aand 122bare extended to the exterior of the resin sealing layer 104, and bonded to the end surface electrodes 122eand 122f, any shield ring or the like defining an electromagnetic shield structure cannot be disposed on the upper surface of the substrate 122. In addition, a problem occurs in that the sealability of the interface between the resin sealing layer 104 and the substrate 122 is degraded.

[0024] In order to overcome the problems described above, preferred embodiments of the present invention provide a surface acoustic wave device which solves the above-described problems of the prior art, and has a surface acoustic wave element mounted on a substrate by a face-down mounting method, can be easily surface-mounted on a printed circuit board or other substrate even when the surface acoustic wave device has a resin sealing layer, has a greatly reduced size of the surface acoustic wave element, is constructed to facilitate easy checking of any fillet formation, prevents any generation of a short circuit or other such defect and disadvantage, and increases versatility in wiring an electromagnetic shield ring or the like.

[0025] A surface acoustic wave device according to a preferred embodiment of the present invention includes a surface acoustic wave element having first and second main surfaces facing each other and a plurality of end surfaces connecting the first and second main surfaces, and an electrode for the surface acoustic wave element and a bump pad for electric connection to the exterior on the first main surface, and a substrate having an electrode land joined with the bump pad of the surface acoustic wave element via a bump, and a resin sealing layer arranged so as to cover the surface acoustic wave element such that the surface acoustic wave element is joined with an upper surface of the substrate from the first main surface side via the bump, and the surface acoustic wave element is spaced from the upper surface of the substrate, the substrate includes a multi-layered substrate, the multi-layered substrate includes a via hole electrode in which one end thereof is connected to the electrode land provided on the upper surface of the multi-layered substrate, an internal electrode connected to the via hole electrode, a mounting electrode provided on a lower surface of the multi-layered substrate, and an end surface wiring electrode with which the electrode for mounting and the internal electrode are connected at an end surface of the multi-layered substrate.

[0026] According to another preferred embodiment of the present invention, the surface acoustic wave device further includes a protective layer which is disposed on the first main surface of the surface acoustic wave element to protect the electrode for the surface acoustic wave element and a frame member which surrounds a portion including the electrode for the surface acoustic wave element to prevent flow of a resin constituting the resin sealing layer.

[0027] According to yet another preferred embodiment of the present invention, the sealing resin is a thermosetting resin or a photosensitive resin.

[0028] According to still another preferred embodiment of the present invention, the multi-layered substrate is preferably made of ceramic or synthetic resin, or other suitable material.

[0029] According to further still another preferred embodiment of the present invention, a shield ring is provided on the upper surface of the multi-layered substrate so as to surround a portion on which surface acoustic wave element is mounted.

[0030] Other features, elements, characteristics and advantages of the present invention will become more apparent from the following detailed description of preferred embodiments of the present invention with reference to the attached drawings.

[0031] FIG. 1 is a frontal sectional view of a surface acoustic wave device according to a first preferred embodiment of the present invention;

[0032] FIG. 2 is a plan view of a multi-layered substrate used in the surface acoustic wave device according to the first preferred embodiment of the present invention;

[0033] FIG. 3 is a bottom plan view of the multi-layered substrate used in the surface acoustic wave device according to the first preferred embodiment of the present invention;

[0034] FIG. 4 is a frontal sectional view of the surface acoustic wave device according to a modification of a preferred embodiment of the present invention;

[0035] FIG. 5 is a fragmentary frontal cross-sectional and broken view for describing another modification of a preferred embodiment of the surface acoustic wave device of the present invention;

[0036] FIG. 6 is a bottom plan view of the surface acoustic wave device according to another modification a preferred embodiment shown in FIG. 5;

[0037] FIG. 7 is a frontal sectional view of an example of a conventional surface acoustic wave device;

[0038] FIG. 8 is a frontal sectional view of another example of the conventional surface acoustic wave device;

[0039] FIG. 9 is a frontal sectional view of yet another example of the conventional surface acoustic wave device;

[0040] FIG. 10 is a bottom plan view for describing a bump pad disposed on a lower surface of the surface acoustic wave element included in the conventional surface acoustic wave device;

[0041] FIG. 11 is a bottom plan view for describing a bump pad disposed on a lower surface of the surface acoustic wave element when the size of the surface acoustic wave element is reduced; and

[0042] FIG. 12 is a frontal sectional view for describing problems when the size of the conventional surface acoustic wave device shown in FIG. 7 is reduced.

[0043] Hereinafter, specific preferred embodiments of the present invention will be described with reference to drawings.

[0044] FIG. 1 is a sectional view of a surface acoustic wave device according to a first preferred embodiment of the present invention. A surface acoustic wave device 1 preferably includes a multi-layered substrate 2, and a surface acoustic wave element 3 bonded on the multi-layered substrate 2 via a bump. The periphery of the surface acoustic wave element 3 is preferably covered by a resin sealing layer 4.

[0045] The surface acoustic wave element 3 has a surface acoustic wave substrate 11. The surface acoustic wave substrate 11 has a structure in which a piezoelectric thin film is disposed on a piezoelectric substrate or an insulation substrate, or a structure in which a piezoelectric thin film is further disposed on a piezoelectric substrate.

[0046] The surface acoustic wave substrate 11 has first and second main surfaces 11aand 11b. An electrode 12 for constituting the surface acoustic wave element 3 such as an IDT is disposed on the first main surface 11a. The structure of the electrode 12 is determined according to the targeted surface acoustic wave element, and not limited in the present invention.

[0047] On the other hand, in the surface acoustic wave element 3, bump pads 13 and 14 are provided on the first main surface 11a. The bump pads 13 and 14 are electrically connected to an electrode 12 for the surface acoustic wave element, and also constitute a portion to be bonded to the substrate via the bump pads 13 and 14.

[0048] In the present preferred embodiment, the multi-layered substrate 2 is preferably formed of ceramic, but it may be formed of synthetic resin or other suitable material. Electrodes 16 and 17 are disposed on an upper surface 2aof the multi-layered substrate 2. In addition, a shield ring 18 in plan view of FIG. 2 is disposed on the upper surface 2aof the multi-layered substrate 2. The shield ring 18 includes a substantially rectangular frame that is preferably formed of the same conductive material as that of the electrodes 16 and 17. Of course, the shield ring 18 may be formed of a conductive material that is different from that of the electrodes 16 and 17. The shield ring 18 is arranged so as to perform electromagnetic shielding of the interior of the shield ring 18.

[0049] The electrodes 16 and 17 are electrically connected to bumps 19aand 19bas shown in the figure. This means that the surface acoustic wave element 3 is bonded to the electrodes 16 and 17 via the bumps 19aand 19b, and mounted on the multi-layered substrate 2.

[0050] On the other hand, via hole electrodes 20aand 20bleading from the upper surface 2ato the position of the middle height of the multi-layered substrate 20 are formed on the multi-layered substrate 2. Upper ends of the via hole electrodes 20aand 20bare electrically connected to the electrodes 16 and 17. In addition, an upper end of the via hole electrode 21 is electrically connected to the shield ring 18 so that the via hole electrode 21 is formed in a similar manner to the via hole electrodes 20aand 20b.

[0051] Internal electrodes 22 and 23 are disposed in the multi-layered substrate 2 at the position of the middle height. The internal electrode 22 is electrically connected to a lower end of the via hole electrode 20a, and the internal electrode 23 is electrically connected to lower ends of the via hole electrodes 20band 21. The internal electrodes 22 and 23 are extended to end surfaces 2cand 2dfacing each other of the multi-layered substrate 2. Mounting electrodes 24 and 25 are disposed on a lower surface 2bof the multi-layered substrate 2. The mounting electrodes 24 and 25 are electrically connected to the internal electrodes 22 and 23 via end surface wiring electrodes 26 and 27 respectively disposed on the end surfaces 2cand 2d.

[0052] FIG. 1 shows a structure of a portion at which the pair of electrode lands 16 and 17 are electrically connected to the pair of mounting electrodes 24 and 25, and as shown in FIG. 2, four electrodes 16 and 17, 16A and 17A are disposed on the upper surface of the multi-layered substrate 2. Among these electrode lands, the electrode lands 17 and 17A are connected to the ground potential, and electrically connected to the upper surface 2aof the multi-layered substrate 2 via a connection electrode 31. In addition, as shown in FIG. 3, four mounting electrodes 24, 25, 24A and 25A are disposed on the lower surface 2bof the multi-layered substrate 2.

[0053] Electric connection of the mounting electrodes 24A and 25A to the electrode lands 16A and 17A is similar to that shown in FIG. 1.

[0054] In the surface acoustic wave device 1 according to the present preferred embodiment, in order to prevent any oscillation of a portion having the electrode 12 for the surface acoustic wave element of the surface acoustic wave element 3, the surface acoustic wave element 3 is mounted on the multi-layered substrate 2 via the bumps 19aand 19bso as to provide a space B between the first main surface 11aof the surface acoustic wave element 3 and the multi-layered substrate 2. The bumps 19aand 19bcan be formed of suitable metals, such as Au and solder. The resin sealing layer 4 is disposed so as to seal the space B.

[0055] A material for constituting the resin sealing layer 4 is not specifically limited, but a thermosetting resin and a photosensitive resin are preferably used. If the resin sealing layer 4 is formed of a thermosetting resin, the resin sealing layer 4 can be rapidly cured when heated, and the resin sealing layer 4 with excellent mechanical strength can be constituted. If the resin sealing layer 4 is formed of a photosensitive resin, and cured by irradiating the light, the resin sealing layer 4 can be formed without heating the surface acoustic wave element 3.

[0056] In the surface acoustic wave device 1 according to the present preferred embodiment, the distance between the adjacent bumps 19aand 19band the distance d between the via hole electrodes 20aand 20bare reduced when the size of the surface acoustic wave element 3 is reduced. However, the internal electrodes 22 and 23 are extended to the end surfaces 2cand 2d, and electrically connected to the mounting electrodes 24 and 25 via the end surface wiring electrodes 26 and 27, and thus, the distance between the mounting electrodes 24 and 25ccan be larger than the distance between the bump pads. Therefore, short circuits or other defects or disadvantages are prevented from occurring between the adjacent mounting electrodes 24 and 25 when mounting the surface acoustic wave device 1 on a printed circuit board or other suitable substrate.

[0057] In addition, since the end surface wiring electrodes 26 and 27 are provided, fillet formation can be visually checked easily and rapidly when the surface acoustic wave device is mounted on a printed circuit board by soldering, or other suitable process.

[0058] In addition, sealability of the space B is also improved since the resin sealing layer 4 is bonded to the upper surface 2aof the multi-layered substrate 2 in a closed annular area.

[0059] Due to the presence of the shield ring 18, the space B, i.e., a portion including the electrode 12 for the surface acoustic wave element, the bumps 10 and 11, etc. is electromagnetically shielded from the exterior, and are therefore prevented from being affected by the external electromagnetic wave, etc.

[0060] As shown in a modification in FIG. 4, a protective layer 31 may be arranged so as to cover at least a portion including the electrode for the surface acoustic wave element 12 of the surface acoustic wave element 3. The protective layer 31 including a silicon compound such as silicon nitride and silicon oxide may be used, and the moisture resistance of the surface acoustic wave element 3 can be improved.

[0061] As shown in FIG. 4, a frame-shaped dam 32 may be formed on the first main surface 11aof the surface acoustic wave element 3 so as to prevent the resin constituting the resin sealing layer 4 from flowing into the space B side. The material constituting the frame-shaped dam 32 is not specifically limited, but thermosetting resin such as polyimide, epoxy and silicone, and a photosensitive resin, or a metal such as solder may be used.

[0062] FIGS. 5 and 6 are fragmentary frontal cross-sectional and broken view and a bottom plan view of still another modification of the surface acoustic wave device of preferred embodiments of the present invention, respectively. In the modification shown in FIG. 4, the frame-shaped dam 32 is arranged to prevent the resin from flowing in the space B side. In this preferred embodiment of the present invention, a plurality of frame-shaped dams may be disposed.

[0063] In the modification shown in FIG. 5, an inner dam 33 and an outer dam 34 are provided. This means that a plurality of surface acoustic wave filters and surface acoustic wave resonators are constituted on the first main surface 11aof the surface acoustic wave element 3 though not shown in FIGS. 5 and 6. The inner dam 33 is arranged so as to surround a portion including each surface acoustic wave filter and each surface acoustic wave resonator. The outer dam 34 is formed on the first main surface 11aso as to surround an entire area including the plurality of surface acoustic wave filter and surface acoustic wave resonators.

[0064] As described above, by providing both the inner dam 33 and the outer dam 34, the resin constituting the resin sealing layer 4 can be reliably prevented from flowing in the space B, in particular, in a portion including each surface acoustic wave filter and each surface acoustic wave resonator therein.

[0065] As shown in FIG. 6, in the surface acoustic wave device according to the modification of preferred embodiments of the present invention, a plurality of mounting electrodes 41 to 46 are disposed on the lower surface of the multi-layered substrate 2. The mounting electrodes 41 to 46 are arranged to extend from the lower surface of the multi-layered substrate 2 leading to notches 2eto 2jmade in a side surface of the multi-layered substrate 2. The mounting electrode 41, as a representative, is connected to the internal electrode 22 disposed in the multi-layered substrate 2 via the end surface wiring electrode 47 formed in the notch 2e. As described above, the notches 2eto 2jmay be provided in the side surface of the multi-layered substrate 2, and the end surface wiring electrode may be formed in the notches 2eto 2j.

[0066] In the surface acoustic wave device of preferred embodiments of the present invention, the surface acoustic wave element is bonded on the multi-layered substrate via the bumps by the face-down mounting method, and in the surface acoustic wave device having the resin sealing layer so as to cover the surface acoustic wave device, the via hole electrodes are disposed with one end thereof bonded to the electrode lands disposed on the upper surface of the multi-layered substrate and bonded to the bumps, the internal electrode connected to the via hole and the mounting electrode formed on the lower surface of the multi-layered substrate are electrically connected to the end surface wiring electrode formed on the end surface of the multi-layered substrate, and the distance between the mounting electrodes can be sufficiently increased even when the size of the surface acoustic wave element is reduced. Therefore, when the surface acoustic wave device is mounted on a printed circuit board or the like by soldering, etc., any short circuit between the adjacent mounting electrodes can be reliably prevented, and fillet formation can be easily and visually checked.

[0067] Since the size of the surface acoustic wave element is significantly reduced, a large number of surface acoustic wave elements can be obtained from one wafer, and the cost of the surface acoustic wave elements can be reduced, and accordingly, the cost of the surface acoustic wave device can be reduced.

[0068] As a result, a compact surface acoustic wave device having excellent sealability and resistance to any short circuit in the mounting can be provided at a low cost.

[0069] In preferred embodiments of the present invention, when the protective film is formed on the first main surface of the surface acoustic wave element, moisture resistance of the surface acoustic wave element can be improved, and when the frame-shaped member is arranged so as to surround a portion including the electrode for the surface acoustic wave element, the flow-in of the resin constituting the resin sealing layer is prevented, and non-defective ratio of the surface acoustic wave device can be increased.

[0070] If a thermosetting resin is used in the resin sealing layer, the resin sealing layer can be rapidly formed when heated, and the resin sealing layer of excellent strength can be obtained. If the resin sealing layer is formed of a photosensitive resin, and cured by light irradiation, the resin sealing layer can be formed without any risk of thermal shock being applied to the surface acoustic wave element.

[0071] When the multi-layered substrate is formed of ceramic, the multi-layered substrate having the internal electrode can be easily obtained by a ceramic-integrated baking technology. In addition, the multi-layered substrate may be constituted by using a synthetic resin, and in such a case, the cost of the multi-layered substrate can be reduced by using an inexpensive synthetic resin film laminate.

[0072] If the shield ring is disposed on an upper surface of the multi-layered substrate, the electrode for the surface acoustic wave element or substrate can be electromagnetically shielded, and the surface acoustic wave device having much more stable characteristics can be provided.

[0073] While preferred embodiments of the invention have been described above, it is to be understood that variations and modifications will be apparent to those skilled in the art without departing the scope and spirit of the invention. The scope of the invention, therefore, is to be determined solely by the following claims.