JP2018074518A - Elastic wave device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a highly reliable elastic wave device in which peeling does not easily occur between a substrate and a protective cover. An elastic wave device including a substrate 2, an excitation electrode, and a cover 9. The cover 9 includes a cover portion 9a for accommodating the excitation electrode and a protective layer 9b located on the upper surface of the cover portion 9a, and has a straight portion 9x and a corner portion 9y in a plan view. The protective layer 9b is located inside the cover portion 9a, and the distance between the outer contour line L1 of the cover portion 9a and the outer contour line L2 of the protective layer 9b is larger at the corner portion 9y than at the straight portion 9x. [Selection diagram] Fig. 3

Description

  The present invention relates to an elastic wave device such as a surface acoustic wave (SAW) device or a thin film acoustic resonator (FBAR).

  2. Description of the Related Art A so-called wafer level package acoustic wave device for the purpose of downsizing and the like is known. In this acoustic wave device, excitation electrodes disposed on the main surface of the element substrate are accommodated in the vibration space. The vibration space is formed by a hollow portion provided in the protective cover. In addition, columnar terminals connected to the excitation electrodes are erected on electrode pads provided on the main surface of the element substrate. As for the columnar terminal, the tip side portion (the portion opposite to the main surface of the element substrate) is exposed from the protective cover, and this exposed portion is soldered to the circuit board so that the acoustic wave device is mounted on the circuit board. (For example, refer to Patent Document 1).

JP 2007-208665 A

  By the way, in the acoustic wave device having the above-described structure, separation may occur between the substrate and the protective cover due to a difference in linear expansion coefficient between the substrate and the protective cover. If peeling occurs between the substrate and the protective cover in this way, peeling proceeds from there and the excitation electrode corrodes, resulting in a decrease in the reliability of the acoustic wave device.

  The present invention has been invented to cope with the above-described problems, and provides an elastic wave device that is less likely to be peeled off between a substrate and a protective cover and has excellent reliability.

  An elastic wave device according to an aspect of the present invention includes a substrate, an excitation electrode, and a cover. The excitation electrode excites an elastic wave located on the upper surface side of the substrate. The cover includes a cover part and a protective layer. A cover part is located on the upper surface of a board | substrate, and accommodates an excitation electrode. The protective layer is made of a material different from that of the cover portion, which is located on the upper surface of the cover portion. And a cover has a linear part and a corner | angular part by planar view. Furthermore, the cover is in plan view, the protective layer is located inside the cover part, and the distance between the outer line of the cover part and the outer line of the protective layer is more in the corner than in the straight part. It ’s a big one.

  ADVANTAGE OF THE INVENTION According to this invention, the highly reliable elastic wave apparatus which suppressed peeling with a board | substrate and a cover can be provided.

Fig.1 (a) is a top view which shows the elastic wave apparatus which concerns on embodiment of this invention, FIG.1 (b) is a top view of the state which removed the protective cover of the surface acoustic wave apparatus shown to Fig.1 (a). It is. It is the II-II side view of Fig.1 (a). It is a principal part enlarged plan view of Fig.1 (a). It is a principal part enlarged plan view which shows the modification of FIG. It is a principal part enlarged plan view which shows the modification of FIG.

  Fig.1 (a) is a top view which shows the elastic wave apparatus 1 which concerns on embodiment of this invention. FIG.1 (b) is a top view of the state which removed the protective cover of the elastic wave apparatus 1 shown to Fig.1 (a). FIG. 2 is a cross-sectional view taken along the line II-II in FIG. FIG. 3 is an enlarged top view of a main part in a region surrounded by a broken line in FIG.

  1 to 3 schematically show the acoustic wave device 1 in order to facilitate understanding of the acoustic wave device 1. In implementation, the size and number of each part of the acoustic wave device 1 are shown. The shape and the like may be set as appropriate.

  In addition, the elastic wave device 1 may be set to either the upper side or the lower side, but the front side of the sheet of FIG.

  The acoustic wave device 1 includes a substrate 2, an excitation electrode 3, a pad 7 connected to the excitation electrode, and a cover 9. Further, in this example, a columnar electrode 15 standing on the pad 7 and penetrating the cover 9 and a bump 19 provided on the columnar electrode 15 are provided.

  The substrate 2 is a rectangular parallelepiped single crystal substrate having piezoelectricity, such as a lithium tantalate single crystal or a lithium niobate single crystal. The substrate 2 has a first main surface 2a (also referred to as an upper surface 2a) and a second main surface 2b on the back side thereof. 1 and 2 illustrate the case where electrodes and the like are disposed only on the first main surface 2a, but electrodes and the like may be disposed also on the second main surface 2b.

  The excitation electrode 3 is located on the first main surface 2 a of the substrate 2. In this example, the excitation electrode 3 has a pair of comb-like electrodes (IDT electrodes). Each comb-like electrode has a bus bar extending in the elastic wave propagation direction on the substrate 2 and a plurality of electrode fingers extending from the bus bar in a direction perpendicular to the elastic wave propagation direction. The two comb-like electrodes are arranged so that the respective electrode fingers mesh with each other.

  Since FIG. 1 and the like are schematic diagrams, an example in which a multi-mode SAW filter in which a plurality of pairs of comb-like electrodes having several electrode fingers are arranged in the propagation direction of the elastic wave is configured. Although shown, actually, a plurality of pairs of comb-like electrodes having more electrode fingers may be provided. Further, a plurality of excitation electrodes 3 may be provided, and a ladder type filter in which they are connected by a connection method such as series connection or parallel connection may be configured, or a resonator is configured by only one excitation electrode 3. Also good. In this example, the reflector is disposed so as to sandwich the comb-like electrode, but this is not restrictive. Such an excitation electrode 3 is formed of an Al alloy such as an Al—Cu alloy.

  A pad 7 that is electrically connected to the excitation electrode 3 is formed on the first main surface 2 a of the substrate 2. The pad 7 is formed of, for example, an Al alloy such as an Al—Cu alloy, like the excitation electrode 3.

  As shown in FIG. 2, the insulating layer 4 covers the excitation electrode 3, a connecting conductor for connecting the excitation electrode 3 and the pad 7, etc., and contributes to preventing oxidation of these conductor layers. The insulating layer 4 is made of, for example, a material having an insulating property and a mass that is light enough not to affect the propagation of elastic waves, and is made of silicon oxide, silicon nitride, silicon, or the like. It is good also as a structure which laminated | stacked these.

  The cover 9 includes a cover portion 9a and a protective layer 9b. Here, the cover portion 9 a covers the excitation electrode 3 from above the insulating layer 4. In this example, the cover portion 9 a constitutes a vibration space 17 for facilitating the propagation of elastic waves on the excitation electrode 3. In other words, the cover portion 9 a includes a frame body 18 a that forms the inner wall of the vibration space 17 and a lid body 18 b that forms the ceiling of the vibration space 17. In other words, the frame 18a surrounds a region where the excitation electrode 3 is located, and the lid 18b is positioned on the frame 18a so as to close the opening of the frame 18a.

  The thickness of the layer constituting the frame 18a and the thickness of the lid 18b may be set as appropriate. For example, the thickness is several μm to 30 μm. The frame 18a and the lid 18b are formed to have substantially the same thickness.

  The frame body 18a and the lid body 18b can be formed of different materials, but are preferably formed of the same material in order to increase the adhesive strength between the frame body 18a and the lid body 18b. The frame 18a and the lid 18b are made of, for example, a photocurable material that is cured by being irradiated with light such as ultraviolet rays or visible light, for example, a negative photoresist. As the photocurable material, for example, a resin curable by radical polymerization such as an acrylic group or a methacryl group can be used. More specifically, a urethane acrylate-based, polyester acrylate-based, or epoxy acrylate-based resin can be used. it can. Moreover, you may use an epoxy resin, a urethane resin, etc.

  As shown in FIG. 2, the vibration space 17 has a substantially rectangular cross section, and is formed so that corners on the lid 18 b side are rounded. Further, the planar shape of the vibration space 17 (the shape of the first main surface 2a in plan view) may be set as appropriate. FIG. 1B shows an inner wall corresponding to the outer periphery of the vibration space 17 with a broken line.

  The protective layer 9b is located on the upper surface of the cover portion 9a. In this example, the outline L2 of the protective layer 9b is located on the inner side of the outline L1 of the cover portion 9a in plan view.

  The protective layer 9b is for protecting the cover portion 9a and is made of an insulating material. The protective layer 9b protects, for example, a conductive layer (not shown) located on the cover portion 9a, reinforces the cover portion 9a by using a material having high hardness or Young's modulus, or reduces stress and impact. Thus, by using a resin material having a high glass transition point, the cover portion 9a can be protected from heat applied when the acoustic wave device 1 is mounted.

  The protective layer 9b is made of a material different from the material constituting the cover portion 9a. For example, polyimide or the like can be used.

  The connection conductor 11 is for connecting the excitation electrode 3 and the predetermined pad 7. For example, the connection conductor 11 is formed on the first main surface 2 a of the substrate 2 in the same manner as the excitation electrode 3. As shown in FIG. 1B, the connection conductor 11 is formed in an appropriate pattern on the first main surface 3 a and is connected to the excitation electrode 3. Further, the connection conductor 11 may intersect with another connection conductor 11 via an insulating member for the convenience of wiring. In this way, the connecting conductors 11 are three-dimensionally crossed using the insulating member, so that the degree of freedom of the arrangement place of the pad 7 is improved and the acoustic wave device 1 can be reduced in size. The insulating member is made of, for example, polyimide resin.

A plurality of pads 7 are provided. In FIG. 1B, the pads 7 are provided at the four corners and the center of the longitudinal side. These include a pad 7 for inputting / outputting a signal to / from the excitation electrode 3 and a pad 7 for connecting the excitation electrode 3 and the like to a reference potential. In addition, an electrically floating pad 7 may be provided. Further, in this example, the pad 7 is formed in the vicinity of the center of the side in addition to the four corners, but may be formed in the middle of the side or only in the four corners.

  These pads 7, the connecting conductors 11, and the excitation electrodes 3 can be produced by the same process using the same material, for example, and their thickness is, for example, 0.1 μm to 1.0 μm.

  The columnar electrode 15 is provided on the electrode pad 7 that is electrically connected to the excitation electrode 3. That is, the columnar electrode 15 is electrically connected to the excitation electrode 3 via the electrode pad 7 and the connecting conductor 11, and functions as a terminal for connecting this to an external electric circuit or ground. In this example, the columnar electrode 15 is provided continuously from the substrate 2 to the middle of the thickness of the protective layer 9b by providing a hole for exposing the pad 7 in the cover portion 9a and the protective layer 9b. A bump 19 is provided on the upper surface of the columnar electrode 15.

  Apart from this, a columnar electrode 15 that is not electrically connected to the excitation electrode 3 may be provided.

Here, the configuration of the cover 9 will be described in detail. FIG. 3 shows an enlarged plan view of a region surrounded by a broken line in FIG. As shown in FIG. 3, the outer shape of the cover 9 is composed of a corner portion 9x and a straight portion 9y in plan view. The corner portion 9x corresponds to four corner portions in this example, and has a curved arc shape.
The straight line portion 9y is located so as to connect the corner portions 9x.

  The positional relationship between the contour line L1 and the contour line L2 at the corner portion 9x and the straight line portion 9y will be described in detail. As described above, since the protective layer 9b is located inside the cover portion 9a in plan view, the outline line L1 and the outline line L2 do not overlap with each other and are spaced apart (distance). According to the elastic wave device 1, the distance between the contour line LI and the contour line L2 is wider at the corner portion 9x than at the straight portion 9y. The distance between the contour line LI and the contour line L2 indicates the shortest distance between the two, and the distance between the perpendicular line drawn from one point on one line to the other line.

  By setting it as such a structure, the stress concentrated on the corner | angular part 9x can be reduced and peeling with the cover 9 and the board | substrate 2 can be suppressed. Although the corner portion 9x is concentrated in shape, there is a risk that the cover 9 and the substrate 2 may be peeled off due to further stress applied by the thermal history. On the other hand, according to the configuration of the present disclosure, by increasing the distance between the contour lines L1 and L2 in the corner portion 9x where the stress is concentrated, the stress concentration portion is shifted, and as a result, the stress is dispersed. Can do. Thereby, the highly reliable elastic wave apparatus 1 can be provided.

  Here, when the cover portion 9a and the protective layer 9b are made of a resin material, and the protective layer 9b is manufactured by thermosetting after the cover portion 9a is formed, the cover portion 9a of the corner portion 9x is pulled due to shrinkage caused by the thermosetting. The cover 9 and the substrate 2 may be peeled off. Even if no peeling occurs, a strong stress is applied to the corner portion 9x, and there is a risk of peeling during a subsequent process or actual use. For this reason, when the cover part 9a and the protective layer 9b consist of resin materials, it is preferable to set it as the structure of this indication especially.

  In particular, when the cover portion 9a and the protective layer 9b are made of a resin material, and the material constituting the protective layer 9b has a larger shrinkage rate than the material constituting the cover portion 9a, the angle caused by the shrinkage at the time of curing. The stress on the part 9x can be relaxed. In addition, when the material constituting the protective layer 9b has a larger Young's modulus and / or linear expansion coefficient than the material constituting the cover portion 9a, thermal stress during use of the acoustic wave device 1 or during mounting It is possible to relieve stress on the corner portion 9x caused by stress or the like.

  Further, in this example, the columnar electrode 15 is located at the corner portion 9x. In this case, in order to reduce the stress applied to the columnar electrode 15, the positional relationship between the outline L1 and the outline L2 may be as described above. With such a configuration, the columnar electrode 15 can be separated from the position where stress is most concentrated.

  In particular, in this example, the curvature of the columnar electrode 15 and the curvature at the corner portion 9x of the outline L2 are the same. In other words, the distance between the columnar electrode 15 and the outline L2 at the corner 9x is constant. Furthermore, in other words, the distance between the outer periphery of the through hole provided in the cover portion 9a and the protective layer 9b and the outline L2 is constant. With such a configuration, it is possible to further relax the stress at the corner 9x and reduce the stress on the columnar electrode 15. Furthermore, since the stress is uniformly applied to the columnar electrode 15, it is possible to provide a highly reliable acoustic wave device 1 without generating a fracture starting point or the like.

  On the other hand, the cover portion 9a extends so as to protrude outward from the protective layer 9b, so that a bonding area with the substrate 2 can be secured.

  As described above, according to the elastic wave device 1 of the present disclosure, the separation between the substrate 2 and the cover 9 can be suppressed and the reliability can be increased.

(Modification)
In the above example, the case where the distance between the columnar electrode 15 and the outline L2 at the corner 9x is constant has been described. However, the distance between the outline LI and the outline L2 is greater at the corner 9x than at the straight line 9y. If it becomes wide, it is not restricted to this example. For example, as shown in FIG. 4, the distance between the columnar electrode 15 and the outline L2 at the corner 9x may be changed.

  In the example shown in FIG. 4, the outer lines L1 and L2 have the largest distance between the outer lines L1 and L2 at the portion where the outer lines L1 and L2 are connected to the straight line connecting the center of the columnar electrode 15 and the four corners of the substrate 2. The distance between the line L2 and the columnar electrode is reduced, and the distance between the outer lines L1 and L2 is decreased toward the straight line portion 9y, and the distance between the outer line L2 and the columnar electrode is increased. It is configured. In other words, when the curvatures of the outer lines L1 and L2 and the outer periphery of the columnar electrode 15 at the corner 9x are compared, the outer line L1, the columnar electrode 15, and the outer line L2 are configured to increase in this order.

  With such a shape, the stress concentrated on the corner portion 9x is dispersed, and the stress applied to the columnar electrode 15 gradually changes, so that the substrate 2 and the cover 9 are peeled off and applied to the columnar electrode 15. The adhesion strength between the cover portion 9a and the protective layer 9b can be maintained while suppressing both stress applications.

(Modification)
In the above example, the case where the outer peripheries (outline) of the frame body 18a and the lid body 18b coincide with each other has been described as an example. FIG. 5 shows an example in which the outer periphery (outline) of the frame 18a and the lid 18b do not match.

  In FIG. 5, the outline of the frame 18a is L11, and the outline of the lid 18b is L12. The lid 18b is located inside the frame 18a in plan view. The distance between the contour line L11 and the contour line L12 is constant between the corner portion 9x and the straight portion 9y. Since the frame body 18a and the lid body 18b are integrally formed to form a single structure, such a configuration increases the strength of the cover portion 9a, and the highly reliable elastic wave device 1 can be obtained. Can be provided. Further, the positioning of the lid 18b with respect to the frame 18a is facilitated, and the productivity can be increased. Furthermore, when the elastic wave device 1 is embedded with a mold resin or the like, the contact area can be increased by the step between the frame 18a and the lid 18b, and the reliability can be improved.

  In particular, when the frame 18a and the lid 18b are made of the same material, such a configuration is preferable. When the frame body 18a and the lid body 18b are made of the same material or both are cured at the same time, in order to make the amount of contraction of both constant, the distance between the outline line L11 and the outline line L12 is: It is preferable that the corner portion 9x and the straight portion 9y remain constant. Furthermore, in the example shown in FIG. 5, the distance between the contour line L12 and the contour line L2 is larger than the distance between the contour line L11 and the contour line L12 at the corner 9x. That is, the terrace constituted by the frame 18a and the lid 18b in the corner portion 9x is narrower than the terrace constituted by the lid 18b and the protective layer 9b. As the resin material is thermally cured, the shrinkage stress is larger at the interface between the lid 18b and the protective layer 9b than at the interface between the substrate 2 and the frame 18a, and the cover 9 is prevented from peeling off from the substrate 2. Can do.

  On the other hand, in the straight line portion 9y, the distance between the contour line L12 and the contour line L2 is smaller than the distance between the contour line L11 and the contour line L12. That is, in the straight portion 9y, the terrace constituted by the frame body 18a and the lid body 18b is wider than the terrace constituted by the lid body 18b and the protective layer 9b. With such a configuration, it is possible to protect the conductor pattern and the like formed on the lid 18b, and to secure a bonding area between the cover portion 9a and the protective layer 9b.

  The present invention is not limited to the above embodiment, and may be implemented in various aspects. For example, the acoustic wave device is not limited to a surface acoustic wave device. For example, the excitation electrode may be a pair of electrodes that sandwich a piezoelectric film constituting a piezoelectric thin film resonator in the thickness direction.

  Moreover, although the example which provided the columnar electrode which penetrates the cover 9 in the four corners was shown in the above-mentioned example, there may not be a columnar electrode and may exist in the center of a side. Similarly, there may be no vibration space.

  Further, the protective layer 9b may be thinner than the lid body 18b. In this case, the amount of heat shrinkage accompanying the curing of the protective layer 9b can be reduced.

1. Surface acoustic wave device (elastic wave device)
2. Piezoelectric substrate (substrate)
2a ... 1st main surface (main surface)
3 ... Comb electrode (excitation electrode)
4 ... Protective layer 9 ... Cover 11 ... Connecting conductor 15 ... Columnar electrode 17 ... Vibration space

Claims (7)

A substrate,
An excitation electrode for exciting an elastic wave located on the upper surface side of the substrate;
A cover part that is located on the upper surface of the substrate and accommodates the excitation electrode; and a protective layer made of a material different from the cover part located on the upper surface of the cover part. A cover having a corner, and
In plan view
The protective layer is located inside the cover part,
The elastic wave device, wherein a distance between an outline of the cover portion and an outline of the protective layer is larger at the corner portion than at the straight portion. In a region in the vicinity of the corner where the cover portion and the protective layer overlap in plan view, the columnar electrode that penetrates the cover portion and at least part of the thickness direction of the protective layer,
2. The acoustic wave device according to claim 1, wherein an outline of the protective layer at a corner of the protective layer is a fixed distance from the columnar terminal in a plan view. The cover portion includes a frame body that surrounds a region where the excitation electrode is located in a plan view, and a lid body that is positioned on the frame body so as to close an opening of the frame body,
In plan view
The lid is located inside the frame;
The elastic wave device according to claim 1 or 2, wherein the distance between the outline of the lid and the outline of the frame is substantially the same between the straight portion and the corner.   The distance between the outline of the lid and the outline of the frame at the corner is smaller than the distance between the outline of the lid and the outline of the protective layer in plan view. 3. The elastic wave device according to 3.   In plan view, the distance between the outline of the lid and the outline of the frame is larger at the straight portion than the distance between the outline of the lid and the outline of the protective layer. The elastic wave device according to claim 4, which is small at a portion.   The elastic wave device according to claim 1, wherein the cover portion and the protective layer have different curvatures in the corner portion in plan view.   The elastic wave device according to claim 1, wherein the protective layer has at least one of a thermal contraction rate, a thermal expansion coefficient, and a Young's modulus greater than that of the cover portion.

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