WO2022181073A1

WO2022181073A1 - Acoustic wave module

Info

Publication number: WO2022181073A1
Application number: PCT/JP2022/000477
Authority: WO
Inventors: 幸一郎川崎
Original assignee: 株式会社村田製作所
Priority date: 2021-02-26
Filing date: 2022-01-11
Publication date: 2022-09-01

Abstract

An acoustic wave module (100) comprises an acoustic wave device (110), a mounting substrate (50), a sealing resin (80), and solder bumps (70a, 70b). The acoustic wave device (110) comprises a piezoelectric substrate (10), a function element (60), a support portion (20), a cover portion (30), wiring patterns (62a, 62b), cover wires (69a, 69b), and through electrodes (64a, 64b). The piezoelectric substrate (10), the support portion (20), and the cover portion (30) form a hollow space (Ar). A surface (S1) of the piezoelectric substrate (10) is exposed from the sealing resin (80). The solder bumps (70a, 70b) are formed at positions that do not overlap the through electrodes (64a, 64b) when the acoustic wave device (100) is seen in plan view.

Description

Acoustic wave module

The present invention relates to an acoustic wave module equipped with an acoustic wave device, and more particularly to a package structure of an acoustic wave module capable of reducing the effects of thermal stress when mounted on a substrate.

In electronic devices such as mobile phones and smartphones, elastic wave modules equipped with elastic wave devices using surface acoustic wave (SAW) or bulk acoustic wave (BAW) resonators are used. 2. Description of the Related Art In recent years, electronic devices have become smaller and thinner, and along with this trend, acoustic wave devices themselves are also desired to be smaller and thinner. In order to achieve this, a WLP (Wafer Level Package) structure has been proposed in which the chip itself of the acoustic wave device itself is used as a package, as disclosed in International Publication No. 2015/159465 (Patent Document 1), for example.

In an acoustic wave device having a general WLP structure, a piezoelectric element is generated in a hollow space formed by a piezoelectric substrate, a support portion arranged around the surface of the piezoelectric substrate, and a cover portion provided on the support portion. It has a configuration in which a plurality of functional elements are arranged on a flexible substrate. In the case of a surface acoustic wave (SAW) device, a comb-like electrode (IDT: Inter Digital Transducer) is arranged as a functional element.

Japanese Patent Application Laid-Open No. 2004-208326 (Patent Document 2) discloses an acoustic wave device having a structure in which a surface acoustic wave element is sealed with a thermosetting resin composition. In Patent Document 2, after the surface acoustic wave element is coated with the thermosetting resin composition, the thermosetting resin composition is ground until the main surface of the piezoelectric substrate included in the surface acoustic wave element is exposed. As a result, it is possible to reduce the height of the elastic wave device itself.

WO2015/159465 Japanese Patent Application Laid-Open No. 2004-208326

A method (reflow) of electrically connecting the acoustic wave device and the mounting board by soldering may be adopted in the acoustic wave module equipped with the acoustic wave device having such a WLP structure. In this case, the elastic wave device and the mounting board are heated to a temperature at which the solder melts (unstressed), and then cooled to room temperature to solidify the solder. The bodies are electrically connected to each other.

In the process of heating the mounting board at a high temperature, the thermosetting resin composition expands and presses the melted solder. After that, in the process of cooling down to room temperature, the solder solidifies while maintaining the shape of the compressed state. As described above, when the thermosetting resin composition shrinks before and after heating, stress (hereinafter also referred to as "thermal stress") is generated in the piezoelectric substrate due to the difference in the shape of the solder. .

When the thermosetting resin composition is not ground and the piezoelectric substrate is fixed by the thermosetting resin composition, the mechanical strength of the piezoelectric substrate is improved. , may not be damaged. However, as disclosed in Patent Document 2, when the thermosetting resin composition is ground to expose the main surface of the piezoelectric substrate in order to achieve a low profile, the piezoelectric substrate is made of the thermosetting resin composition. is not fixed by That is, the piezoelectric substrate is likely to break due to thermal stress caused by deformation of the solder.

The present invention has been made to solve such problems, and its object is to reduce the thermal stress generated in the mounting process in an acoustic wave module in which an acoustic wave device having a WLP structure is mounted. is.

An elastic wave module including an elastic wave device according to the present invention comprises a mounting substrate on which the elastic wave device is mounted, a sealing resin that covers at least a part of the elastic wave device and is arranged on the mounting substrate, and an elastic wave Solder bumps are provided for electrically connecting the device and the mounting substrate. An acoustic wave device includes a piezoelectric substrate, a plurality of functional elements formed on the piezoelectric substrate, a support portion arranged on the piezoelectric substrate around a region in which the plurality of functional elements are formed, and a support member. a cover portion arranged to face the piezoelectric substrate via a portion; a wiring pattern formed on the piezoelectric substrate and electrically connected to a part of the plurality of functional elements; A first conductive portion and a second conductive portion electrically connecting the wiring pattern and the first conductive portion are provided between the wiring pattern and the first conductive portion. A hollow space Ar is formed by the piezoelectric substrate, the supporting portion, and the cover portion, and a plurality of functional elements are arranged in the hollow space Ar. A first surface of the piezoelectric substrate is exposed from the sealing resin. The solder bump is formed at a position that does not overlap the second conductive portion when the elastic wave device is viewed from above.

According to the present invention, in the acoustic wave device having the WLP structure, when the acoustic wave device is viewed from above, the solder bumps used for connection with the mounting substrate electrically connect the wiring pattern and the first conductive portion. It is formed at a position not overlapping with the second conductive portion. This makes it possible to reduce the thermal stress generated in the mounting process.

1 is a cross-sectional view of an elastic wave module equipped with an elastic wave device according to Embodiment 1; FIG. FIG. 4 is a cross-sectional view of an elastic wave module equipped with an elastic wave device of a comparative example; FIG. 3 is a diagram for explaining thermal stress generated in the cooling process in the elastic wave module of the comparative example in FIG. 2; FIG. 11 is an enlarged view of a contact portion between a piezoelectric substrate and a support portion in Modification 2; It is sectional drawing of the ZY plane and XY plane of an elastic wave apparatus. It is a comparative example of the elastic wave device shown in FIG. It is a figure which shows the modification regarding arrangement|positioning of a penetration electrode.

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. The same or corresponding parts in the drawings are denoted by the same reference numerals, and the description thereof will not be repeated.

[Embodiment 1]
FIG. 1 is a cross-sectional view of elastic wave module 100 equipped with elastic wave device 110 according to the first embodiment. Acoustic wave device 110 in the present embodiment will be described as an example of a surface acoustic wave device including an IDT electrode as a functional element, but the acoustic wave device may use bulk waves.

In the following description, the thickness direction of the mounting board 50 is defined as the Z-axis direction, and the plane perpendicular to the Z-axis direction is defined as the X-axis and the Y-axis. In addition, the positive direction of the Z-axis in each drawing may be referred to as the upper surface side, and the negative direction thereof as the lower surface side.

Referring to FIG. 1, elastic wave device 110 includes piezoelectric substrate 10, lid 40, functional element 60,

wiring patterns

62a and 62b, through

electrodes

64a and 64b, and

wirings

69a and 69b on the cover. Prepare. The lid body 40 includes a support portion 20 and a cover portion 30 . The mounting substrate 50 includes

connection terminals

52a and 52b. Acoustic wave device 110 and mounting substrate 50 are connected to each other via

solder bumps

70a and 70b. A sealing resin 80 is filled on the mounting substrate 50 .

The piezoelectric substrate 10 is, for example, a piezoelectric substrate made of a piezoelectric material such as lithium tantalate (LiTaO3) or lithium niobate (LiNbO3). Alternatively, it may be a laminated substrate in which a piezoelectric thin film made of the above piezoelectric material is laminated on a support substrate made of alumina, silicon (Si), and sapphire. Furthermore, a laminated substrate in which one or more layers of insulating films made of silicon oxide, silicon nitride, or the like are interposed between the piezoelectric thin film and the support substrate may be used. On the other hand, the mounting board 50 is made of resin such as phenol or epoxy.

At least one functional element 60 is arranged on the main surface of the piezoelectric substrate 10 on the negative direction side of the Z axis. Functional element 60 is formed using, for example, an electrode material such as a single metal made of at least one of aluminum, copper, silver, gold, titanium, tungsten, platinum, chromium, nickel, and molybdenum, or an alloy containing these as main components. Also included is a pair of IDT electrodes. A surface acoustic wave resonator is formed by the piezoelectric substrate 10 and the IDT electrodes. The

conductive wiring patterns

62a, 62b, the through

electrodes

64a, 64b, and the

wirings

69a, 69b on the cover are made of metal such as copper or aluminum.

In the piezoelectric substrate 10, a support portion 20 made of resin is provided around the region where the functional element 60 is formed. A hollow space Ar is formed around the plurality of functional elements 60 including the IDT electrodes by arranging the cover 30 so as to face the main surface of the piezoelectric substrate 10 on which the functional elements 60 are arranged via the support 20 . It is formed. As a result, the surface acoustic wave propagates in the portion of the piezoelectric substrate 10 adjacent to the hollow space Ar. On-

cover wirings

69a and 69b are formed on the main surface of the cover portion 30 on the negative direction side of the Z-axis. The cover wiring 69a electrically couples the solder bump 70a and the through electrode 64a. In addition, the on-cover wiring 69b electrically couples the solder bump 70b and the through electrode 64b.

Wiring patterns

62a and 62b for electrically connecting the functional elements 60 are arranged on the main surface of the piezoelectric substrate 10 on the negative direction side of the Z axis. The wiring pattern 62a is electrically connected to the on-cover wiring 69a via a through electrode (via) 64a penetrating through the supporting portion 20 and the cover portion 30. As shown in FIG. In addition, the wiring pattern 62b is electrically connected to the on-cover wiring 69b via a through electrode (via) 64b penetrating through the supporting portion 20 and the cover portion 30. As shown in FIG. The wiring 69a on the cover extends in the positive direction of the Y-axis of the elastic wave device 110 from the connection portion with the through electrode 64a and is connected to the solder bump 70a. In addition, the wiring 69b on the cover extends in the negative direction of the Y-axis of the acoustic wave device 110 from the connection portion with the through electrode 64b and is connected to the solder bump 70b. Solder bumps 70a and 70b are electrically connected to

connection terminals

52a and 52b on mounting substrate 50, respectively.

In the process of forming elastic wave module 100 in Embodiment 1, after elastic wave device 110 is mounted on mounting substrate 50 , sealing resin 80 is applied on mounting substrate 50 so as to cover the periphery of elastic wave device 110 . be filled. Thereby, the mechanical strength of the elastic wave module 100 is improved. Further, in the elastic wave module 100 according to the first embodiment, the sealing resin 80 filled on the positive direction side of the Z-axis with respect to the elastic wave device 110 is ground in order to reduce the height of the elastic wave module 100 . As a result, the surface S1 of the piezoelectric substrate 10 is exposed. That is, as shown in FIG. 1, the sealing resin 80 is in a state of covering surfaces of the elastic wave device 110 other than the surface S1. Note that the surface S1 corresponds to the "first surface" of the present disclosure. Moreover, in the present embodiment, the support portion 20 and the cover portion 30 are provided as separate members, but they may be provided as an integrated unit.

Here, in the elastic wave module 100 according to Embodiment 1, the solder bumps 70a are formed at positions that do not overlap the through electrodes 64a when the elastic wave device 110 is viewed from above. Similarly, the solder bumps 70b are formed at positions that do not overlap the through electrodes 64b when the acoustic wave device 110 is viewed from above. In the first embodiment, the

wirings

69a and 69b on the cover correspond to the "first conductive portion" in the present disclosure, and the through

electrodes

64a and 64b correspond to the "second conductive portion" in the present disclosure. Further, in the elastic wave module 100, in addition to the elastic wave device 110, other elastic wave devices or devices other than the elastic wave device (chip components, semiconductor devices, etc.) are further mounted on the mounting substrate 50 and sealed. You can stop.

FIG. 2 is a cross-sectional view of an elastic wave module 100# equipped with an elastic wave device 110# of a comparative example. In elastic wave device 110# of the comparative example in FIG. 2, unlike elastic wave device 110 in FIG. The difference is that through

electrodes

64a and 64b in 30 are directly connected to

solder bumps

70a and 70b. As a result, the solder bumps 70a and 70b are formed at positions overlapping the through

electrodes

64a and 64b, respectively, when the elastic wave device 110 is viewed from above.

In the reflow process for mounting the

acoustic wave devices

110 and 110# shown in FIGS. 1 and 2 on the mounting board 50, the paste-like solder shown on the solder bumps 70a and 70b is applied, and then the acoustic wave device to be mounted is applied. is placed on a predetermined position and heated in a high-temperature furnace in that state. As a result, the solder is melted and then cooled to room temperature, whereby the elastic wave device and the mounting substrate 50 are electrically connected. Instead of paste solder, flux containing powder solder may be sandwiched between the acoustic wave device and the mounting board 50 and heated.

As described above, in order to reduce the height of the elastic wave device, the filled sealing resin 80 is ground on the positive side of the Z axis, and the surface S1 of the piezoelectric substrate 10 is exposed. That is, the piezoelectric substrate 10 is not fixed on the positive direction side of the Z-axis.

FIG. 3 is a diagram for explaining the thermal stress generated during the cooling process in elastic wave module 100# of the comparative example in FIG. With reference to FIG. 3, the left diagram (A) shows the state during the heating process, and the right diagram (B) shows the state during the cooling process. As shown in left figure (A), in the heating process, the sealing resin 80 expands and presses the solder bumps 70a. As a result, the compressed solder bumps 70a are deformed so as to extend in the Z-axis direction as shown in the right figure (B).

In the process of cooling to room temperature, the solder bumps 70a are solidified while being pressed as shown in the right figure (B). In the process of shrinking the sealing resin 80 during cooling, the solidified solder bumps 70a push up the through electrodes 64a and the wiring patterns 62a arranged on the positive side of the Z axis in the positive direction of the Z axis. As a result, stress concentration occurs at the connecting portion between the wiring pattern 62a and the piezoelectric substrate 10, which may cause damage to the piezoelectric substrate 10. FIG.

On the other hand, in the elastic wave device 110 according to the first embodiment shown in FIG. 1, the solder bumps 70a and 70b are not directly connected to the through

electrodes

64a and 64b, respectively, but through the

wirings

69a and 69b on the cover. It is connected. Since the

wirings

69a and 69b on the cover extend in the direction along the main surface of the cover portion 30 (the Y-axis direction in the drawing) and have a length, they are pushed up from the solder bumps 70a and 70b in the positive direction of the Z-axis. However, the through

electrodes

64a and 64b and the

wiring patterns

62a and 62b are not pushed up in the positive direction of the Z axis.

That is, in the first embodiment, when the acoustic wave device 110 is viewed from above, the solder bumps 70a and 70b are not formed at positions overlapping the through

electrodes

64a and 64b, respectively. , the through

electrodes

64a and 64b are not directly affected by the deformation of the solder bumps 70a and 70b. Therefore, the stress concentration between the

wiring patterns

62a and 62b and the piezoelectric substrate 10 can be reduced by adopting the configuration of the first embodiment.

In addition, when the elastic wave device 110 is viewed from above, the solder bumps 70a and 70b are formed at positions overlapping with the hollow space Ar. The distance between the bumps 70a and the solder bumps 70b is shortened, and the width of the acoustic wave device 110 (dimension in the Y-axis direction in the drawing) can be reduced. This increases the degree of design freedom on the piezoelectric substrate 10 and contributes to miniaturization of the device.

(Modification 1)
1 to 3 of Embodiment 1, the positional relationship between the solder bumps 70a and 70b and the through

electrodes

64a and 64b when the acoustic wave device 110 is viewed from above has been described. FIG. 4 is an enlarged view of the contact portion between the piezoelectric substrate 10 and the support portion 20 in Modification 1. As shown in FIG.

The elastic wave module 100B of Modification 1 of Embodiment 1 shown in FIG. 4 further includes a resin layer 31 arranged between the wiring pattern 62a and the piezoelectric substrate 10. The hardness of the resin layer 31 is smaller than that of the wiring pattern 62a. That is, the material of the resin layer 31 is softer than the material of the wiring pattern 62a.

Therefore, even if thermal stress is generated in the wiring pattern 62a so as to push it up in the positive direction of the Z axis, the resin layer 31 absorbs the force pushed up in the positive direction of the Z axis. That is, the resin layer 31 functions as a cushion between the wiring pattern 62a and the piezoelectric substrate 10. As shown in FIG. The resin layer 31 may be arranged between the wiring pattern 62b and the piezoelectric substrate 10 as well.

By adopting a configuration like Modification 1, stress concentration between the

wiring patterns

62a and 62b and the piezoelectric substrate 10 can be reduced.

(Arrangement of Through Silicon Via)
1 to 4, the configuration in which the solder bumps 70a and 70b do not overlap the through

electrodes

64a and 64b when the acoustic wave device 110 is viewed from above has been described. The arrangement of the through electrodes will be described below.

FIG. 5 is a cross-sectional view of the ZY plane and the XY plane of the elastic wave device 110. FIG. 5A is a cross-sectional view of the elastic wave device 110 along the ZY plane, and FIG. 5B is a cross-sectional view along the line II-II of FIG. 5A along the XY plane.

With reference to FIG. 5(B), the support portion 20 has a rectangular frame shape when the elastic wave device 110 is viewed from above. That is, the support portion 20 includes regions 20La and 20Lb forming long sides of the rectangular frame shape and regions 20Sa and 20Sb forming short sides of the rectangular frame shape. A space is formed inside the support portion 20 to form the hollow space Ar described in FIG. Therefore, as shown in FIG. 5B, the shape of the support portion 20 on the XY plane along the line II-II is a frame shape.

As shown in FIG. 5(B), the acoustic wave device 110 includes a plurality of through electrodes 64a-64d and a plurality of solder bumps 70a-70d. In the support portion 20, through

electrodes

64a and 64c are arranged in the region 20La, and through

electrodes

64b and 64d are arranged in the region 20Lb. The through electrodes 64a-64c are connected to the solder bumps 70a-70d through the wirings 69a-69d on the cover, respectively. FIG. 6 is a comparative example of the elastic wave device 110 shown in FIG. In the elastic wave device of the comparative example, through

electrodes

64a and 64b are arranged in the region 20Sa of the supporting portion 20. As shown in FIG. Through

electrodes

64c and 64d are arranged in the region 20Sb.

As mentioned above, the acoustic wave module undergoes heat treatment and cooling treatment in the reflow process. In the heat treatment and cooling treatment, expansion and contraction occur not only in the sealing resin 80 but also in the mounting substrate 50 and the piezoelectric substrate 10 . In the example of FIG. 3, the thermal stress in the Z-axis direction due to the deformation of the solder bumps 70a has been described. also occurs.

The thermal stress in the Y-axis direction is generated, for example, by the shrinkage of the mounting substrate 50, which pulls the solder bumps 70a to 70d inward. As described above, since the material of the piezoelectric substrate 10 is different from the material of the mounting substrate 50, the coefficient of linear expansion of the piezoelectric substrate 10 and the coefficient of linear expansion of the mounting substrate 50 are different from each other under temperature change. Therefore, when the linear expansion coefficient of the mounting substrate 50 is larger than that of the piezoelectric substrate 10, the degree of contraction of the mounting substrate 50 is greater than that of the piezoelectric substrate 10 during the cooling process.

In this case, referring to FIG. 5(A), the shrinkage of the mounting substrate 50 causes the solder bumps 70a to be pulled in the positive direction of the Y axis. Also, the solder bumps 70b are pulled in the negative direction of the Y-axis due to the shrinkage of the mounting substrate 50 . That is, in the elastic wave device 110, thermal stress is generated that pulls the elastic wave device 110 inward.

As shown in FIG. 5(B), the shape of the elastic wave device 110 on the XY plane is a rectangle including long sides and short sides. Generally, since the shrinkage of the mounting board 50 is isotropic, the degree of shrinkage in the long side direction (X direction) is greater than the degree of shrinkage in the short side direction (Y direction).

Therefore, in the elastic wave module 100 of the present embodiment, the through

electrodes

64a and 64c are formed at positions overlapping the regions 20La forming the long sides. Further, the through

electrodes

64b and 64d are formed at positions overlapping with the regions 20Lb forming the long sides. In this manner, in the example of FIG. 5, in the supporting portion 20, the solder bumps 70a to 70d paired with the plurality of through electrodes 64a to 64d are arranged in the Y-axis direction. As a result, the through electrodes are formed in the regions 20Sa and 20Sb, and the solder bumps 70a to 70d paired with the plurality of through electrodes 64a to 64d are arranged in the X-axis direction (comparative example in FIG. 6). ), the mechanical strength of the acoustic wave module 100 is improved.

FIG. 7 is a diagram showing a modification regarding the arrangement of through electrodes. 1 to 5, an example in which the through electrodes 64a to 64h are formed in the support portion 20 has been described. As shown in FIG. 7, the through electrodes 64a to 64h may be formed in the hollow space Ar instead of inside the support portion 20. As shown in FIG. That is, the through electrodes 64a to 64h are formed so as to be exposed without being covered with the support portion 20 in the region overlapping the hollow space Ar when the elastic wave device 110 is viewed from above. The through electrodes 64a to 64h may be formed at positions that do not overlap the cover portion 30 when the elastic wave device 110 is viewed from above. That is, the through electrodes 64a to 64h may be formed outside the support portion 20. FIG.

The embodiments disclosed this time should be considered illustrative in all respects and not restrictive. The scope of the present invention is indicated by the scope of the claims rather than the above description, and is intended to include all changes within the meaning and scope equivalent to the scope of the claims.

10 Piezoelectric substrate, 20 Support portion, 20 La, 20 Lb, 20 Sa, 20 Sb Regions, 30 Cover portion, 31 Resin layer, 50 Mounting substrate, 52 a, 52 b Connection terminals, 62 a, 62 b Wiring patterns, 60 Functional elements, 64 a to 64 h Penetration Electrodes, 69a, 69b: Wiring on the cover, 70a to 70h: Solder bumps, 80: Sealing resin, 100: Elastic wave module, 110, 110A, 110B: Elastic wave device, S1: Surface, Ar: Hollow space.

Claims

An elastic wave module comprising an elastic wave device, the elastic wave module comprising:
a mounting substrate on which the elastic wave device is mounted;
a sealing resin covering at least a portion of the acoustic wave device and arranged on the mounting substrate;
a solder bump for electrically connecting the acoustic wave device and the mounting board;
The elastic wave device is
a piezoelectric substrate having a first surface;
a plurality of functional elements formed on the piezoelectric substrate;
a support portion disposed around the region in which the plurality of functional elements are formed on the piezoelectric substrate;
a lid body including a cover portion arranged to face the piezoelectric substrate via the support portion;
a wiring pattern formed on the piezoelectric substrate and electrically connected to a part of the plurality of functional elements;
a first conductive portion formed on the cover portion and connected to the solder bump;
a second conductive portion electrically connecting the wiring pattern and the first conductive portion between the wiring pattern and the first conductive portion;
A hollow space is formed by the piezoelectric substrate, the support portion, and the cover portion, and the plurality of functional elements are arranged in the hollow space,
The first surface is exposed from the sealing resin,
The elastic wave module, wherein the solder bump is formed at a position not overlapping the second conductive portion when the elastic wave device is viewed from above.
The elastic wave module according to claim 1, wherein the plurality of functional elements include IDT (Inter Digital Transducer) electrodes, and the piezoelectric substrate and the IDT electrodes form a surface acoustic wave resonator.
The elastic wave module according to claim 1 or 2, wherein the solder bumps are formed in a region overlapping with the hollow space when the elastic wave device is viewed from above.
The elastic wave module according to any one of claims 1 to 3, wherein the elastic wave device further comprises a resin layer arranged between the wiring pattern and the piezoelectric substrate.
The support portion has a rectangular frame shape including a first region forming long sides and a second region forming short sides when the acoustic wave device is viewed from above,
the solder bump is connected to the second conductive portion through the first conductive portion;
The elastic wave module according to any one of claims 1 to 4, wherein the second conductive portion is formed at a position overlapping with the first region when the elastic wave device is viewed from above.
The elastic wave module according to any one of claims 1 to 4, wherein the second conductive portion is formed in a region overlapping with the hollow space when the elastic wave device is viewed from above.