Surface acoustic wave device

Abstract

A surface acoustic wave device is provided in which a stress-induced breakage caused by a temperature change is suppressed. A wall portion is provided so as to surround an IDT (interdigital transducer) provided on a surface of a piezoelectric substrate, and a ceiling portion is provided so as to block a region surrounded by the wall portion. Furthermore, a lead electrode is provided on one face of the piezoelectric substrate so as to lead from a position connected to the IDT to the outside of the region surrounded by the wall portion, and an electrode wiring is provided which is electrically connected to the lead electrode by being stacked on the lead electrode outside the wall portion and is led around to an upper face of the ceiling portion. Also, when a protective film is provided so as to cover the upper face of the ceiling portion, the protective film is provided so as to avoid a region in which the electrode wiring is stacked on the lead electrode, in the case where the protective film is provided so as to cover a wider region than the upper face of the ceiling portion.

Description

TECHNICAL FIELD

[0001] The present application relates to a surface acoustic wave device including an inter digital transducer (IDT). BACKGROUND

[0002] In recent years, the miniaturization of communication devices such as mobile phones is rapidly progressing. With the miniaturization of such devices, the miniaturization of electronic parts such as surface acoustic wave devices (SAW devices) and the like, which are constituent parts thereof, is required.

[0003] As a structure for miniaturizing a surface acoustic wave device, a structure of a wafer level-chip size packaging (WL-CSP) type is known. The surface acoustic wave device of the WL-CSP type is a structure in which, for example, as described in Patent Literature 1, comb electrodes are provided on the surface of a piezoelectric substrate, and a peripheral wall layer and a ceiling are provided around the comb electrodes to form a hollow structure to form a working space of the comb electrodes. Further, a structure is described in which lead-out wiring connected to the comb electrodes is led out to the outer edge of the piezoelectric substrate, and further, side wiring connecting the lead-out wiring and a mounting terminal provided on the upper surface of the ceiling is provided. In addition, in Patent Literature 2, a structure is described in which, in an elastic wave device in which the periphery of the comb electrode is surrounded by a cover member, and an epoxy-based sealing resin is provided so as to cover the cover member and the first electrode, which is an electrode electrically connected to the comb electrode, is provided on the outer surface of the cover member.

[0004] In recent years, the reliability of the operation of the acoustic wave device is required to be improved, and the impact test on the product is becoming strict. Therefore, a technology for producing a surface acoustic wave device that is more robust and has high reliability is required.

[0005] [Related Art Literature]

[0006] [Patent Literature]

[0007] [Patent Literature 1] Japanese Patent Application Laid-Open No. 2016-66989

[0008] [Patent Literature 2] Japanese Patent Application Laid-Open No. 2015-39209 SUMMARY

[0009] [Problems to be Solved by the Invention]

[0010] The present application is completed in such a situation, and suppresses the influence of stress applied by temperature change in a surface acoustic wave device.

[0011] [Technical Means for Solving the Problems]

[0012] The surface acoustic wave device of the present application includes: an IDT provided on one face of a piezoelectric substrate;

[0013] a wall portion provided on the piezoelectric substrate and surrounding a region in which the IDT is arranged;

[0014] a ceiling portion plugging an opening of the region surrounded by the wall portion;

[0015] an extraction electrode provided on one face of the piezoelectric substrate and arranged to extract from a position connected to the IDT to the outside of the region surrounded by the wall portion;

[0016] an electrode wiring electrically connected to the extraction electrode by being laminated on the extraction electrode at a portion extracted to the outside of the wall portion and routed on the upper surface of the ceiling portion via a side surface of the wall portion; and

[0017] a protective film provided so as to cover at least the upper surface of the ceiling portion, and

[0018] in a case where the protective film is provided so as to cover a region wider than the upper surface of the ceiling portion, the protective film is provided so as to avoid a region in which the electrode wiring is laminated on the extraction electrode.

[0019] [Effects of the Invention]

[0020] In the surface acoustic wave device of the present application, a wall portion is provided so as to surround an IDT provided on a surface of a piezoelectric substrate, and a ceiling portion is provided so as to plug a region surrounded by the IDT. Further, an extraction electrode is provided on one face of the piezoelectric substrate to extract from a position connected to the IDT to the outside of the region surrounded by the wall portion, and an electrode wiring is provided, which is electrically connected to the extraction electrode by being laminated on the extraction electrode at a portion extracted to the outside of the wall portion and routed on the upper surface of the ceiling portion. Also, in providing a protective film covering the upper surface of the ceiling portion, in a case where the protective film is provided so as to cover a region wider than the upper surface of the ceiling portion, the protective film is provided so as to avoid a region in which the electrode wiring is laminated on the extraction electrode. Thus, when the surface acoustic wave device is exposed to temperature changes, the breaking of the piezoelectric substrate near the connection portion of the electrode wiring and the extraction electrode can be suppressed by the stress based on the difference in the amount of expansion and contraction of the protective film and the piezoelectric substrate and the extraction electrode, and the disconnection between the electrode wiring and the extraction electrode caused by the breaking can be suppressed. BRIEF DESCRIPTION OF DRAWINGS

[0021] Figure 1 is a longitudinal side view of a surface acoustic wave device.

[0022] Figure 2 is a plan view of a surface acoustic wave device.

[0023] Figure 3 is a diagram showing a configuration example of a conventional surface acoustic wave device.

[0024] Figure 4 is a diagram showing a case where a crack occurs in a conventional surface acoustic wave device.

[0025] Figure 5 is a longitudinal sectional view of another example of a surface acoustic wave device.

[0026] [Explanation of symbols]

[0027] 10: piezoelectric substrate

[0028] 2: IDT

[0029] 31: wall portion

[0030] 32: ceiling portion

[0031] 4: lead electrode

[0032] 6: electrode wiring

[0033] 8: protective film DETAILED DESCRIPTION

[0034] A surface acoustic wave device according to an embodiment of the present application will be described. Figure 1 、 Figure 2 A longitudinal sectional view and a plan view of a surface acoustic wave device are shown. The surface acoustic wave device includes a rectangular flat piezoelectric substrate 10 composed of, for example, lithium tantalate. In the approximate center of one face of the piezoelectric substrate 10, a comb-shaped electrode (IDT) 2 is provided, for example, with titanium (Ti) as a base and laminated with aluminum (Al). In addition, in an actual surface acoustic wave device, a plurality of IDTs 2 are provided, but in the present embodiment, only one IDT 2 is shown. Figure 1 、 Figure 2 In the present embodiment, the number of IDTs 2 is reduced and a simplified description is made.

[0035] In addition, two lead electrodes 4 are provided on the surface of the piezoelectric substrate 10. The two lead electrodes 4 are connected at one end to the bus bars of the IDT 2, and the other end of each lead electrode 4 is led to the one end side and the other end side in the longitudinal direction of the piezoelectric substrate 10, respectively. The lead electrodes 4 are composed of Ti as a base and laminated with Al, like the IDT 2, but are formed thicker than the IDT 2. In addition, the lead electrodes 4 are formed so as to cover the IDT 2. Figure 1 、 Figure 2 The symbol 11 in the present embodiment is an interlayer insulating film.

[0036] Further, a cover member 3 in a rectangular shape in plan view is provided on the piezoelectric substrate 10, and serves to secure a working space for vibration of the IDT 2, and is composed of a resin such as photosensitive polyimide, for example. The cover member 3 includes a wall portion 31 that surrounds the region on the piezoelectric substrate 10 where the IDT 2 is disposed, and a ceiling portion 32 that is provided on the wall portion 31 and plugs the opening of the region surrounded by the wall portion 31. The wall portion 31 is a rectangular ring-shaped member that is provided so as to surround the central region of the piezoelectric substrate 10. When viewed in the longitudinal direction of the piezoelectric substrate 10, the two wall portions 31 that are disposed facing each other with the central region interposed therebetween and extend in the short direction of the piezoelectric substrate 10 are each disposed so as to cross the lead electrodes 4.

[0037] That is, it can be said that the lead electrodes 4 are provided so as to lead from the positions connected to the IDT 2 to the outside of the region surrounded by the wall portion 31. Further, in the present specification, the portions of the two lead electrodes 4 that are outside the wall portion 31 will be referred to as terminal portions 4A.

[0038] Further, the surface acoustic wave device includes electrode wiring 6 that is electrically connected to each terminal portion 4A and is led around via the side surface of the wall portion 31 to the upper surface of the ceiling portion 32. The electrode wiring 6 is formed by, for example, electrolytic plating of copper (Cu). Further, in the present example, the electrode wiring 6 is laminated on the terminal portions 4A (lead electrodes 4) so as to cover the entirety of the terminal portions 4A.

[0039] Further, in the surface acoustic wave device of the present example, in order to protect the constituent members (lead electrodes 4 or wall portion 31, ceiling portion 32, etc.) from impact or corrosion, a protective film 8 composed of, for example, photosensitive epoxy resin is provided. The protective film 8 is provided so as to cover at least the upper surface of the ceiling portion 32. The protective film 8 can also be provided so as to cover a wider region than the upper surface of the ceiling portion 32, and in the example shown in FIG. 8, the side surface of the ceiling portion 32 is also covered by the protective film 8. Figure 1 Figure 2

[0040] On the other hand, the protective film 8 of the embodiment is provided so as to avoid the regions where the electrode wiring 6 is laminated on the lead electrodes 4, that is, the terminal portions 4A, even when provided so as to cover a wider region than the upper surface of the ceiling portion 32. Regarding this aspect, in the surface acoustic wave device shown in FIG. 8, the protective film 8 is not formed on the piezoelectric substrate 10 that is outside the region surrounded by the wall portion 31 including the side surface of the wall portion 31 and the terminal portions 4A. Figure 1 Figure 2

[0041] ​​​​As explained above, the reason for defining the area used to install the protective film 8 is that, in recent years, the requirements for the reliability of surface acoustic wave (SAW) devices have increased. Therefore, the conditions for testing conducted before product shipment have become more stringent. For example, in the thermal shock test based on Japanese Industrial Standards (JIS) C 60068-2-14, the following thermal shock test is specified: A SAW device is alternately placed in a low-temperature bath and a high-temperature bath, which are set to low-temperature exposure temperature and high-temperature exposure temperature, and is alternately exposed to each temperature environment, thereby applying thermal shock. In this thermal shock test, the time for exposing the SAW device to the environments in the low-temperature bath and the high-temperature bath, and the number of cycles of alternating exposure are set.

[0042] Regarding the aforementioned aspects, in recent years, there has been a tendency to conduct thermal shock tests with a larger temperature difference between low-temperature and high-temperature exposure temperatures. From this perspective, examples include setting the low-temperature exposure temperature to, for example, -55°C and the high-temperature exposure temperature to, for example, 125°C. Furthermore, according to experiments, there are also cases where the low-temperature exposure temperature is set to, for example, -60°C and the high-temperature exposure temperature is set to, for example, 150°C. Moreover, assuming a thermal shock test is repeated 750 times, where the surface acoustic wave device is exposed for 30 minutes in a low-temperature bath at each exposure temperature, 15 minutes at room temperature (25°C), and 30 minutes in a high-temperature bath, such tests, for example, remove products that exhibit defects such as component breakage, and only products that pass the test are shipped.

[0043] During the thermal shock test, the components constituting the surface acoustic wave device expand and contract with temperature changes. However, the photosensitive epoxy resin constituting the protective film 8 exhibits a coefficient of linear expansion of approximately 50 ppm / °C, resulting in significant expansion and contraction relative to thermal changes. In contrast, lithium tantalate constituting the piezoelectric substrate 10 has a coefficient of linear expansion of approximately 10 ppm / °C, which is smaller than that of the protective film 8, thus resulting in less expansion and contraction relative to thermal changes.

[0044] Therefore, as Figure 3 As shown, when the protective film 8 is provided in such a way that it even covers the area where the lead-out electrode 4 (terminal part 4A) and the electrode wiring 6 are stacked, large stress is generated near the interface between the protective film 8 and the electrode wiring 6 as the amount of expansion and contraction of the protective film 8 and the electrode wiring 6 varies.

[0045] Due to the stress, a load is applied to the lead-out electrode 4 or the piezoelectric substrate 10, sometimes for example, as... Figure 4The piezoelectric substrate 10 on the lower side of the connection portion of the electrode wiring 6 and the lead-out electrode 4 (terminal portion 4A) is broken as shown. With the generation of the breakage of the piezoelectric substrate 10, the connection portion of the electrode wiring 6 or the lead-out electrode 4 (terminal portion 4A) is sometimes broken, and wire breakage occurs.

[0046] As has been described, since a thermal shock test with a large temperature difference is performed in recent years, stress between the protective film 8 and the piezoelectric substrate 10 based on the difference in linear expansion coefficient is in a tendency to be stronger, and a tendency that breakage is more likely to occur is assumed. Therefore, when the thermal shock test is performed, there is a concern that the yield of products of the structure shown is decreased. Figure 3 、 Figure 4 The structure shown in the product.

[0047] In contrast to this, in the surface acoustic wave device of the embodiment, the protective film 8 is provided so as to avoid the region in which the electrode wiring 6 and the lead-out electrode 4 (terminal portion 4A) are laminated. With the structure, breakage of the piezoelectric substrate 10 or wire breakage of the electrode wiring 6 and the lead-out electrode 4 (terminal portion 4A) can be suppressed.

[0048] In particular, the linear expansion coefficient of the photosensitive epoxy resin is large, and therefore the amount of expansion and contraction between the protective film 8 and the piezoelectric substrate 10 is large when the temperature is changed in the elastic wave device in which the material of the protective film 8 is the photosensitive epoxy resin. Therefore, in the case where the protective film 8 is provided so as to cover the piezoelectric substrate 10, the piezoelectric substrate 10 is easily broken. Therefore, in the elastic wave device in which the material of the protective film 8 is the photosensitive epoxy resin, in the case where the region in which the lead-out electrode 4 and the electrode wiring 6 are laminated is provided on the piezoelectric substrate 10, it is preferable that the protective film 8 is provided so as to avoid the region.

[0049] This is not limited to the photosensitive epoxy resin, and is the same, for example, in the case where the protective film 8 is formed using a material with a linear expansion coefficient exceeding 52 ppm / °C.

[0050] On the other hand, since the top plate portion 32 or the wall portion 31 composed of the resin such as the photosensitive polyimide is not largely different in linear expansion coefficient from the photosensitive epoxy resin, stress that causes breakage of the top plate portion 32 or the wall portion 31 is not easily generated even if a thermal shock test with a large temperature difference is performed. In addition, the resin is also high in flexibility compared to the piezoelectric substrate 10, and therefore breakage is not easily generated.

[0051] Therefore, in the case where the material of the protective film 8 is the photosensitive epoxy resin, Figure 1 、 Figure 2In the example shown, a protective film 8 is provided to cover the upper surface and sides of the top plate portion 32, protecting the constituent components disposed in the area from impact or corrosion. Therefore, the area where the protective film 8 is provided can be further expanded, even to cover the sides of the wall portion 31. However, in this case, it is necessary to form the protective film 8 in a manner that the lower end of the protective film 8 does not contact the area where the lead-out electrodes 4 and electrode wiring 6 are stacked, or to remove the lower end of the protective film 8 that is formed in contact with the stacked area.

[0052] In addition, such as Figure 5 As shown, in surface acoustic wave devices, an electrode protective film 9 can also be provided in the area exposed by the protective film 8 that is not covered by the electrode wiring 6 to protect the electrode wiring 6. The electrode protective film 9 can, for example, be made of nickel (Ni) / gold (Au) plating. Figure 5 In the example shown, an electrode protective film 9 is provided to cover the area where the electrode wiring 6 and the lead-out electrode 4 are stacked, as well as the surface of the electrode wiring 6 formed on the outer side of the wall portion 31. By providing the electrode protective film 9 in the area of ​​the electrode wiring 6 not covered by the protective film 8 as described above, the electrode wiring 6 can be protected from breakage caused by impacts such as collisions between components.

Claims

1. A surface acoustic wave device, characterized by, Comprising: an interdigital transducer provided on one face of a piezoelectric substrate; a wall portion provided on the piezoelectric substrate and surrounding an area in which the interdigital transducer is disposed; a top plate portion that plugs an opening of the area surrounded by the wall portion; a lead electrode provided on one face of the piezoelectric substrate and provided so as to lead out from a position connected to the interdigital transducer to the outside of the area surrounded by the wall portion; an electrode wiring electrically connected to the lead electrode by being laminated on the lead electrode at a portion leading out to the outside of the wall portion and led around via a side surface of the wall portion to an upper surface of the top plate portion; and a protective film provided so as to cover at least the upper surface of the top plate portion, and in a case where the protective film is provided so as to cover an area wider than the upper surface of the top plate portion, the protective film is provided so as to avoid an area in which the electrode wiring is laminated on the lead electrode.

2. The surface acoustic wave device according to claim 1, wherein the protective film is composed of a photosensitive epoxy resin.

3. The surface acoustic wave device according to claim 1 or 2, wherein a linear expansion coefficient of the protective film is 52 ppm / °C or more.

4. The surface acoustic wave device according to claim 1 or 2, wherein an electrode protective film composed of a material having a smaller linear expansion coefficient than the protective film is included on a surface of the electrode wiring in an area not covered by the protective film.

5. The surface acoustic wave device according to claim 3, wherein an electrode protective film composed of a material having a smaller linear expansion coefficient than the protective film is included on a surface of the electrode wiring in an area not covered by the protective film. ​

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