Surface acoustic wave device

Abstract

A surface acoustic wave device includes a piezoelectric substrate, a wall formed on one face of the piezoelectric substrate and made of synthetic resin, and a cover supported by the wall and made of synthetic resin, an internal space being formed among the piezoelectric substrate, the wall, and the cover. The surface acoustic wave device further has a through-hole that penetrates the cover and the wall, the through-hole being used to accommodate a solder bump that electrically connects an electrode pattern on the piezoelectric substrate to the outside, the through-hole including an enlarged diameter portion located in the cover, a reduced diameter portion located in the wall and having a smaller cross-sectional area than the enlarged diameter portion, and a step formed between the enlarged diameter portion and the reduced diameter portion, the enlarged diameter portion having at least two outer side wall portions that are arranged at intervals in a direction around a central axis of the through-hole and have distances from the central axis that are increased, and an inner side wall portion formed between adjacent outer side wall portions and having a distance from the central axis that is smaller than the distances from the central axis of the outer side wall portions. With this, a closed gap that is a main cause of flux residue around the solder bump is not formed.

Description

Technical Field

[0001] This invention relates to an improvement of a surface elastic wave device. Background Technology

[0002] Figure 9 This diagram illustrates the structure of a surface elastic wave device in a wafer-level package (WLP) configuration. In the WLP-configured surface elastic wave device, an electrode pattern including comb-shaped electrodes is formed on one side of a piezoelectric substrate 100, and a wall 101 made of synthetic resin and a cover 102 made of synthetic resin and supported by the wall 101 are disposed on this surface, thereby forming an internal space 103 (cavity) between the piezoelectric substrate 100, the wall 101, and the cover 102.

[0003] The cover 102 and the wall 101 are provided with through holes 105 for electrically connecting the electrode pattern to the outside via welding bumps 104. The through hole 105 includes an enlarged diameter portion 105a located in the cover 102, a reduced diameter portion 105b located in the wall 101 with a cross-sectional area smaller than the enlarged diameter portion 105a, and a step 106 formed between the enlarged diameter portion 105a and the reduced diameter portion 105b.

[0004] Here, after solder paste is applied to the surface of the piezoelectric substrate 100 by printing through the through-hole 105, a reflow soldering process is performed to spherize the solder bumps 104. That is, since the synthetic resin has no affinity with the solder paste, the solder paste melted by the reflow soldering process agglomerates into a spherical shape due to its surface tension when it comes into contact with the opening of the expanded diameter portion 105a of the synthetic resin cover 102.

[0005] Therefore, in a conventional WLP (Wave-Loop) surface elastic wave device, the shape of the profile of the enlarged diameter portion 105a at the cross-section perpendicular to the central axis of the through hole 105 is simply circular. Consequently, in a conventional WLP surface elastic wave device, a closed void 107 is formed between the portion of the welding protrusion 104 that connects to the opening of the enlarged diameter portion 105a and the step 106.

[0006] The flux contained in the solder paste should be removed by cleaning after the reflow soldering process. However, because the gap 107 in the conventional WLP surface elastic wave device is closed, there is a problem that the flux residue in the gap 107 cannot be removed. Summary of the Invention

[0007] The main problem that this invention aims to solve is to prevent the formation of closed gaps around the welding bumps of such surface elastic wave devices, which are the main cause of flux residue.

[0008] To solve the above-mentioned technical problems, the surface elastic wave device of the present invention comprises:

[0009] A piezoelectric substrate having an electrode pattern containing comb-shaped electrodes formed on one side;

[0010] A wall formed on the surface of the piezoelectric substrate and made of synthetic resin; and

[0011] A cover, supported by the wall and made of synthetic resin, forms an internal space between the piezoelectric substrate, the wall, and the cover.

[0012] The surface elastic wave device also has a through hole penetrating the cover and the wall, the through hole being used to accommodate welding bumps that electrically connect the electrode pattern to the outside.

[0013] The through hole includes an enlarged diameter portion located within the cover body, a reduced diameter portion located within the wall body with a cross-sectional area smaller than the enlarged diameter portion, and a step formed between the enlarged diameter portion and the reduced diameter portion.

[0014] The enlarged diameter portion has at least two outer sidewall portions and an inner sidewall portion located between two adjacent outer sidewall portions. The at least two outer sidewall portions are spaced apart in the direction surrounding the central axis of the through hole and are at a large distance from the central axis. The distance between the inner sidewall portion and the central axis is smaller than the distance between the outer sidewall portion and the central axis.

[0015] In one embodiment of the invention, a groove extending along the central axis is formed within the enlarged diameter portion, and the bottom side of the groove becomes the outer wall portion.

[0016] In one embodiment of the invention, a plurality of the grooves are formed such that the portion between adjacent grooves in the direction surrounding the central axis becomes the inner sidewall portion, and the inner sidewall portion is formed by an arc along an imaginary circle centered on the central axis.

[0017] In one embodiment of the invention, the cross-sectional profile of the expanded diameter portion in a direction perpendicular to the central axis is formed to have a side portion extending along the sides of an imaginary quadrilateral centered on the central axis, and a corner portion located at the corner of the quadrilateral, wherein the side portion constitutes the inner wall portion and the corner portion constitutes the outer wall portion.

[0018] In one embodiment of the invention, a groove extending along the central axis is formed within the enlarged diameter portion, the groove having a pair of groove sidewalls and a groove bottom wall intersecting the groove sidewalls, the groove bottom wall becoming the outer sidewall portion.

[0019] In one embodiment of the invention, the thickness of the cover is greater than the thickness of the wall.

[0020] In one embodiment of the present invention, the end face of the wall in the thickness direction, the end face of the cover in the thickness direction, and the end face of the piezoelectric substrate in the thickness direction are all located on the same imaginary plane.

[0021] In one embodiment of the invention, the surface elastic wave device has a plurality of said through holes, with a gap between adjacent said through holes in the direction surrounding the internal space.

[0022] In one embodiment of the invention, the through hole has an opening and is respectively formed with welding bumps. Each welding bump has a base and a spherical portion located within the reduced diameter portion of the corresponding through hole. The spherical portion has a lower portion formed on a corresponding step and located within a corresponding expanded diameter portion, and an upper portion protruding outward from the corresponding opening.

[0023] In one embodiment of the invention, an open gap is formed between the lower portion of each welded protrusion and the corresponding outer sidewall portion.

[0024] The beneficial effect of the present invention is that, according to the present invention, an open gap can be formed around the welding bump in such a surface elastic wave device, so that the flux remaining in this gap can be properly removed during the cleaning process after reflow soldering.

[0025] Furthermore, when constructing a module comprising a wiring substrate having the surface elastic wave device of the present invention mounted thereon and a molding resin covering the mounting side of the wiring substrate, the molding resin can be allowed to penetrate into the gaps. In this way, the present invention has the effect of improving the mechanical stability of the module constructed in this way. Attached Figure Description

[0026] Figure 1 This is a cross-sectional view of a surface elastic wave device (first embodiment) according to an embodiment of the present invention.

[0027] Figure 2 This shows the formation location of the through hole of the welding bump in the first embodiment; the top view of the structure after the welding bump is omitted.

[0028] Figure 3 yes Figure 2 A cross-sectional view of the location of line AA in the middle.

[0029] Figure 4 yes Figure 2 Cross-sectional diagram at the location of the middle BB line.

[0030] Figure 5 This is a cross-sectional view showing the process of making the first embodiment have welding bumps, wherein (a), (b), and (c) in the same figure represent the order of the process.

[0031] Figure 6 It is a cross-sectional view showing the manufacturing process of the module including the first embodiment, wherein (a), (b), (c), and (d) in the same figure represent the order of the process.

[0032] Figure 7 This shows the formation location of the through hole of the welding bump in a surface elastic wave device (second embodiment) according to an embodiment of the present invention. The top view of the structure after showing the welding bump is omitted.

[0033] Figure 8 This shows the formation of the through hole of the welding bump in a surface elastic wave device (third embodiment) according to an embodiment of the present invention. The top view of the structure after showing the welding bump is omitted.

[0034] Figure 9 This is a cross-sectional diagram showing the structure of a conventional WLP (Surface Elastic Wave) device. Detailed Implementation

[0035] The following will be based on Figures 1 to 8 This invention describes an embodiment of a surface elastic wave device 1. The surface elastic wave device 1 of this embodiment has a wafer-level package (WLP) structure.

[0036] Figure 1 This cross-sectional structure is shown. The WLP structure of the surface elastic wave device 1 includes: a piezoelectric substrate 2 on one side 2a having an electrode pattern 3 including comb-shaped electrodes; a wall 4 formed on the surface 2a of the piezoelectric substrate 2 and made of synthetic resin; and a cover 5 supported by the wall 4 and made of synthetic resin, forming an internal space 6 (air cavity) between the piezoelectric substrate 2, the wall 4 and the cover 5.

[0037] The piezoelectric substrate 2 is typically a quadrilateral plate. In the WLP structure, the internal space 6 on the electrode pattern 3 is formed by forming the wall 4 surrounding the electrode pattern 3 on one side 2a of the piezoelectric substrate 2, and then forming the cover 5 on the wall 4. In the illustrated example, the outer periphery of the cover 5 is integrated with the end of the wall 4 protruding from the piezoelectric substrate 2 to form a plate. The surface elastic wave device 1 is formed such that the end face 4a in the thickness direction of the wall 4, the end face 5a in the thickness direction of the cover 5, and the end face 2b in the thickness direction of the piezoelectric substrate 2 are all located on the same imaginary plane.

[0038] Through holes 8 are formed on the cover 5 and the wall 4 for electrically connecting the electrode pattern 3 to the outside with welding bumps 7. The through holes 8 penetrate the cover 5 and the wall 4 in a direction perpendicular to the surface 2a of the piezoelectric substrate 2, with the terminal portion 3a of the electrode pattern 3 located at the bottom of the through hole 8. Typically, there are multiple through holes 8, with a gap between adjacent through holes 8 in the direction surrounding the internal space 6.

[0039] Each through hole 8 includes an enlarged diameter portion 8a located within the cover body 5, a reduced diameter portion 8b located within the wall body 4 and perpendicular to the central axis x (a straight line extending along the continuous direction of the through hole 8 through the center of the through hole 8) with a smaller cross-sectional area than the enlarged diameter portion 8a, and a step 8c formed between the enlarged diameter portion 8a and the reduced diameter portion 8b. The step 8c is formed around the central axis x of the through hole 8. The profile shape of the cross-section of the enlarged diameter portion 8a perpendicular to the central axis x is the same at any position of the enlarged diameter portion 8a, and the profile shape of the cross-section of the reduced diameter portion 8b perpendicular to the central axis x is also the same at any position of the reduced diameter portion 8b.

[0040] Each through hole 8 is formed with a welding bump 7. Each welding bump 7 has a base 7a located within the reduced diameter portion 8b and a spherical portion 7b. The spherical portion 7b has a lower portion 7ba formed on the step 8c and located within the expanded diameter portion 8a, and an upper portion 7bb protruding outward from the opening 8d of the through hole 8. The main part of the forming process of the welding bump 7 is as follows: Figure 5 As shown.

[0041] First, a wall 4 and a cover 5 with through holes 8 are formed at predetermined positions on the piezoelectric substrate 2 (step 1 / Figure 5 (a) in the middle.

[0042] Next, solder paste 9 is applied to surface 2a of the piezoelectric substrate 2 via through-hole 8 using a printing method (step 2 / Figure 5 (b) in the middle.

[0043] Then, reflow soldering is used to form solder bumps 7 from the molten solder paste 9 (step 3 / Figure 5 (c) In the state of contact with the orifice 8d of the through hole 8 of the synthetic resin wall 4 (that is, the orifice of the enlarged diameter portion 8a), the molten solder paste 9 solidifies into a spherical shape, forming the spherical portion 7b.

[0044] In this implementation, such as Figure 2 , Figure 7 , Figure 8 As shown, the enlarged diameter portion 8a has a central axis x surrounding the through hole 8 (see reference). Figure 5At least two outer wall portions 8aa are spaced apart in the direction of (a) and the distance from the central axis x is increased. An inner wall portion 8ab is formed between two adjacent outer wall portions 8aa. The distance between the inner wall portion 8ab and the central axis x is less than the distance between the outer wall portion 8aa and the central axis x.

[0045] In this way, a welding protrusion 7 can be formed in contact with the inner wall portion 8ab, and an open gap 10 is formed between the welding protrusion 7 (i.e., the lower part 7ba of the welding protrusion 7) formed at the step 8c and the outer wall portion 8aa.

[0046] This allows for the proper removal of flux residues within the voids 10 during the cleaning process following reflow soldering.

[0047] Furthermore, when solder paste 9 is applied to the surface 2a of the piezoelectric substrate 2 by printing through the through-hole 8, air can also be discharged through the gap 10, so that the solder paste 9 can be printed properly and smoothly.

[0048] In addition, when constructing a module 11 (composite product) having a wiring substrate 11b (on which the surface elastic wave device 1 is mounted) and a molding resin 11a covering the mounting side of the wiring substrate 11b, the molding resin 11a can be allowed to penetrate into the gap 10, thereby improving the mechanical stability of the module 11 constructed in this way.

[0049] Figure 6 This shows the main part of the manufacturing process of module 11.

[0050] First, the terminal portion 11c of the wiring substrate 11b (see reference) is printed. Figure 6 Solder paste 9 is attached to (a) in step 1 / Figure 6 (b) in the middle.

[0051] Next, with the corresponding surface elastic wave device 1 welding bump 7 on the terminal portion 11c in step 1, reflow soldering is performed to electrically connect the welding bump 7 to the terminal portion 11c (step 2 / Figure 6 (b) to (c)). Finally, on the mounting side of the wiring substrate 11b, a molding resin 11a is applied to embed the surface elastic wave device 1 into the molding resin 11a (step 3 / Figure 6 (d)

[0052] If the cross-sectional profile of the expanded diameter portion 8a is formed as a simple circle, a closed void 10 will be formed between the portion of the welding protrusion 7 that contacts the opening of the expanded diameter portion 8a and the step 8c. In contrast, in the surface elastic wave device 1 of this embodiment, the solder paste 9, which is melted by reflow soldering, solidifies into a spherical shape in contact with the opening 8d of the through hole 8 of the synthetic resin wall 4 (i.e., the portion formed by the inner sidewall portion 8ab in the opening of the expanded diameter portion 8a), thereby forming a spherical portion 7b. Therefore, the void 10 can be formed in an open state between the spherical portion 7b and the outer sidewall portion 8aa of the expanded diameter portion 8aa.

[0053] Figures 1-6 In the first embodiment shown, a groove 12 extending along the central axis x is formed within the enlarged diameter portion 8a, that is, on the wall of the through hole 8 within the enlarged diameter portion 8a, and the bottom side of the groove 12 becomes the outer wall portion 8aa. In this first embodiment, several grooves are formed such that the portion between adjacent grooves 12 in the direction surrounding the central axis x becomes the inner wall portion 8ab, and the inner wall portion 8ab is formed by an arc along an imaginary circle centered on the central axis x. The profile shape of the groove 12 in a cross section perpendicular to the central axis x is semi-circular. In the direction surrounding the central axis x, adjacent grooves 12 are spaced substantially equally at all positions. Furthermore, in this first embodiment, any groove 12 in the direction surrounding the central axis x faces another groove 12 across the central axis x.

[0054] With this configuration, in this first embodiment, a gap 10 can be formed when the spherical portion 7b of the welding protrusion 7 is linearly connected to the inner sidewall portion 8ab, wherein the portion between adjacent inner sidewall portions 8ab can be open in the direction around the central axis x.

[0055] For example, when the maximum diameter L1 of the spherical portion 7b of the welding bump 7 (see...) Figure 4 The diameter is set to 100 μm, and the formed narrowed section 8b is a circular hole with a diameter L2 (see reference). Figure 2 The distance L3 between the inner wall portions 8ab of the expanded diameter portion 8a located at a relative position on both sides of the central axis x is 80 μm (see...). Figure 3 The distance L4 between the outer wall portions 8aa of the expanded diameter portion 8a, which are 90 μm in diameter and located on opposite sides of the central axis x, is defined as (see [reference]). Figure 4 When the diameter is set to 110 μm, the gap 10 between the spherical part 7b and the outer wall part 8aa of the expanded diameter part 8a is 10 μm.

[0056] Figure 7The second embodiment is shown, wherein the groove 12 has a pair of groove sidewalls 12b and a groove bottom wall 12a intersecting the groove sidewalls 12b, the groove bottom wall 12a becoming the outer sidewall portion 8aa. In this second embodiment, the other configurations are substantially the same as in the first embodiment, so description is omitted.

[0057] Figure 8 This shows a third embodiment, in which the cross-sectional profile of the expanded diameter portion 8a in a direction perpendicular to the central axis x is formed to have an imaginary quadrilateral y along the central axis x (see [reference]). Figure 8 The imaginary quadrilateral y has a side portion 13 extending from its side, and a corner portion 14 located at the corner of the quadrilateral y. The side portion 13 forms the inner wall portion 8ab, and the corner portion 14 forms the outer wall portion 8aa. In the illustrated example, the intersection of the two diagonals of the imaginary quadrilateral y becomes the center of the central axis x. Furthermore, the corner portion 14 is substantially along an imaginary line segment z that intersects the side portion 13 at a substantially 45-degree angle (see [reference]). Figure 8 The cross-sectional profile of the expanded diameter portion 8a in the direction perpendicular to the central axis x is substantially octagonal.

[0058] Therefore, in this third embodiment, when the spherical portion 7b of the welding protrusion 7 is in point contact with the four inner sidewall portions 8ab, an open gap 10 is formed between adjacent contact portions in the direction surrounding the central axis x.

[0059] Furthermore, in the embodiment described above, the thickness of the cover 5 (the dimension of the cover 5 in the direction perpendicular to the surface 2a of the piezoelectric substrate) is greater than the thickness of the wall 4 (the dimension of the wall 4 in the direction perpendicular to the surface 2a of the piezoelectric substrate). Thus, as described above, solder paste 9 is applied to the surface 2a of the piezoelectric substrate 2 via the through-hole 8 using a printing method (step 2 / Figure 5 When (b) is used, it is easy to increase the amount of solder paste 9 in the diameter expansion section 8a.

[0060] Of course, the present invention is not limited to the embodiments described above, and the scope of the present invention includes all embodiments that can achieve the purpose of the present invention.

Claims

1. A surface elastic wave device, comprising: A piezoelectric substrate having an electrode pattern containing comb-shaped electrodes formed on one side; A wall formed on the surface of the piezoelectric substrate and made of synthetic resin; and A cover, supported by the wall and made of synthetic resin, forms an internal space between the piezoelectric substrate, the wall, and the cover. The surface elastic wave device also has a through hole penetrating the cover and the wall, the through hole being used to accommodate welding bumps that electrically connect the electrode pattern to the outside. The through hole includes an enlarged diameter portion located within the cover body, a reduced diameter portion located within the wall body with a cross-sectional area smaller than the enlarged diameter portion, and a step formed between the enlarged diameter portion and the reduced diameter portion. Its features are: The enlarged diameter portion has at least two outer sidewall portions and an inner sidewall portion located between two adjacent outer sidewall portions. The at least two outer sidewall portions are spaced apart in a direction surrounding the central axis of the through hole. The distance between the inner sidewall portion and the central axis is less than the distance between the outer sidewall portion and the central axis.

2. The surface elastic wave device according to claim 1, characterized in that: A groove extending along the central axis is formed within the enlarged diameter portion, and the bottom side of the groove becomes the outer wall portion.

3. The surface elastic wave device according to claim 2, characterized in that: A plurality of the grooves are formed such that the portion between adjacent grooves in the direction surrounding the central axis becomes the inner sidewall portion, and the inner sidewall portion is formed by an arc along an imaginary circle centered on the central axis.

4. The surface elastic wave device according to claim 1, characterized in that: The cross-sectional profile of the expanded portion in a direction perpendicular to the central axis is formed to have a side portion extending along the side of an imaginary rectangle centered on the central axis, and a corner portion located at the corner of the rectangle, the side portion constituting the inner wall portion, and the corner portion constituting the outer wall portion.

5. The surface elastic wave device according to claim 1, characterized in that: The enlarged diameter portion has a groove extending along the central axis, the groove having a pair of groove sidewalls and a groove bottom wall intersecting the groove sidewalls, the groove bottom wall becoming the outer sidewall portion.

6. The surface elastic wave device according to any one of claims 1 to 4, characterized in that: The thickness of the cover is greater than the thickness of the wall.

7. The surface elastic wave device according to claim 1, characterized in that: The end faces of the wall in the thickness direction, the end faces of the cover in the thickness direction, and the end faces of the piezoelectric substrate in the thickness direction are all located on the same imaginary plane.

8. The surface elastic wave device according to claim 1, characterized in that: The surface elastic wave device has a plurality of through holes, with a gap between adjacent through holes in the direction surrounding the internal space.

9. The surface elastic wave device according to claim 3, characterized in that: The through holes have openings and are respectively formed with welding protrusions. Each welding protrusion has a base and a spherical portion located in the reduced diameter portion of the corresponding through hole. The spherical portion has a lower portion formed on the corresponding step and located in the corresponding expanded diameter portion, and an upper portion protruding outward from the corresponding opening.

10. The surface elastic wave device according to claim 9, characterized in that: An open gap is formed between the lower part of each welded protrusion and the corresponding outer wall portion.

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