Acoustic wave device

Abstract

To provide a new structure for an acoustic wave device having a CSP structure, which can efficiently release heat generated in a device chip to the outside while ensuring high mechanical integrity between a sealing portion and a package substrate.SOLUTION: An acoustic wave device includes a sealing portion 4 that includes a first portion 4a covering a non-functional surface 3b facing a functional surface 3a of a device chip 3, and a second portion 4b extending from the first portion 4a to a surface 2a of a package substrate 2, covering a side surface 3c of the device chip 3 that corresponds to the thickness of the device chip 3, and that forms an internal space 6 between the functional surface 3a of the device chip 3 and the surface 2a of the package substrate 2. The package substrate 2 is provided with a plurality of metallic pillar portions 2e that protrude from the surface 2a and are built into the second portion 4b of the sealing portion 4.SELECTED DRAWING: Figure 2

Description

Technical Field

[0001] The present invention relates to an improvement of an elastic wave device suitable for use as a frequency filter or the like in a mobile communication device or the like.

Background Art

[0002] As an electronic component including a surface acoustic wave (SAW) element having a CSP (Chip Size Package) structure, there is one disclosed in Patent Document 1. The one in this Patent Document 1 has a structure in which a SAW element (device chip) mounted on a support member (package substrate) via an opposing space is covered with a sealing portion formed on the support member, and the opposing space is used as an internal space.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] The main problem to be solved by the present invention is to provide a new structure capable of efficiently releasing heat generated in a device chip to the outside by inputting a signal to an elastic wave device while ensuring high mechanical integrity between a sealing portion and a package substrate in an elastic wave device having a CSP structure.

Means for Solving the Problems

[0005] In order to achieve the above object, in the present invention, an elastic wave device includes a package substrate and a device chip mounted on the package substrate with a functional surface having a functional element including an IDT electrode facing the one surface of the package substrate, and A first portion covering a non-functional surface of the device chip facing the functional surface of the device chip, and a second portion following the first portion and covering a side surface that is the thickness of the device chip between the functional surface and the non-functional surface and reaching the one surface of the package substrate, and a sealing portion forming an internal space between the functional surface of the device chip and the one surface of the package substrate. The package substrate is provided with a plurality of metal pillar portions protruding from the one surface and built in the second portion of the sealing portion.

[0006] One aspect of the present invention is to make the contact area between the pillar portion and the sealing portion three times or more the contact area between the pillar portion and the package substrate.

[0007] Also, one aspect of the present invention is to make all or part of the surface of the pillar portion a rough surface.

[0008] Also, one aspect of the present invention is to form the pillar portion so that its thickness gradually increases as it approaches the protruding end portion.

[0009] Also, one aspect of the present invention is to make the protruding end portion side of the pillar portion head-shaped.

[0010] Also, one aspect of the present invention is to electrically connect the pillar portion to a ground pattern formed on the package substrate.

[0011] Also, one aspect of the present invention is to provide a plurality of the pillar portions with a space therebetween in a direction of going around the device chip in a state of viewing the elastic wave device from a direction orthogonal to the one surface of the package substrate.

[0012] Also, making the height of the pillar portion greater than the distance between the functional surface of the device chip and the one surface of the package substrate is one aspect of the embodiments of this invention.

Advantages of the Invention

[0013] In the surface acoustic wave device according to this invention, the pillar portion can highly ensure the mechanical integrity between the sealing portion and the package substrate, and efficiently conduct the heat generated in the device chip to the package substrate and release it to the outside.

Brief Description of the Drawings

[0014]

Figure 1

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Figure 11

Embodiments for Carrying Out the Invention

[0015] Hereinafter, typical embodiments of this invention will be described with reference to FIGS. 1 to 11. The elastic wave device 1 according to this embodiment is suitable for use as a frequency filter or the like in a mobile communication device or the like.

[0016] Such an elastic wave device 1 includes a device chip 3 mounted on one surface 2a of a package substrate 2 with its functional surface 3a facing the surface 2a. On the functional surface 3a of the device chip 3, a resonator 7a as a functional element 7 including an IDT electrode 7b (see FIG. 4) is formed.

[0017] Typically, the device chip 3 is configured to have a rectangular plate shape with a side length of 0.5 to 1 mm and a thickness of 0.15 to 0.2 mm. Further, the package substrate 2 is configured to have a rectangular plate shape with a side length of 0.7 to 3 mm and a thickness of 0.15 to 0.2 mm. The elastic wave device 1 has a thickness of about 0.4 to 0.6 mm. Typically, the elastic wave device 1 has a hexahedral shape with two rectangular surfaces and four side surfaces on the thickness side.

[0018] Its cross-sectional structure is shown in FIGS. 2 and 3. In the figures, reference numeral 3 is the device chip, reference numeral 3a is its functional surface, reference numeral 3b is the non-functional surface facing the functional surface 3a, and reference numeral 7a is the resonator. Between the device chip 3 and the package substrate 2, there is an intervening protruding electrode 10 (bump) that electrically connects the wiring 8 formed on the device chip 3 (description thereof is omitted in FIGS. 1 to 3) and the wiring 2b formed on the package substrate 2 side, and a gap 5 is formed for this protruding electrode 10. On the other surface 2c of the package substrate 2 opposite to the one surface 2a on the mounting side of the device chip 3, external connection terminals 2d for connecting the elastic wave device 1 to a mother board (not shown) are formed.

[0019] In this way, from the state where the device chip 3 is mounted on the one surface 2a of the package substrate 2, a sealing portion 4 is formed on the one surface 2a of the package substrate 2. Such a sealing portion 4 is composed of a resin having insulating properties. Typically, after mounting the device chip 3 on the collective substrate 13 (see FIG. 6) that becomes the package substrate 2 using the protruding electrode 10, the resin is applied to the mounting side of this collective substrate 13 with a predetermined thickness, and then this resin is heated to a predetermined temperature and cured to form the sealing portion 4. Alternatively, after mounting the device chip 3 on the collective substrate 13 that becomes the package substrate 2 using the protruding electrode 10, a sheet having a predetermined thickness made of the resin is laminated on the mounting side of this collective substrate 13, and this sheet is heated to a predetermined temperature and once melted and then cured to form the sealing portion 4. The sealing portion 4 formed in this way includes a first portion 4a that covers the non-functional surface 3b of the device chip 3 facing the functional surface 3a of the device chip 3, and a second portion 4b that follows the first portion 4a and covers the side surface 3c having the thickness of the device chip 3 between the functional surface 3a and the non-functional surface 3b and reaches the one surface 2a of the package substrate 2. And, by the sealing portion 4 formed in this way, an internal space 6 (also referred to as a hollow structure portion or an air cavity, etc.) is formed between the functional surface 3a of the device chip 3 and the one surface 2a of the package substrate 2. That is, the sealing portion 4 hermetically seals the gap 5 over the entire circumference of the device chip 3, whereby the internal space 6 is formed between the functional surface 3a of the device chip 3 and one surface 2a of the package substrate 2. The sealing portion 4 is formed after the formation of the pillar portion 2e described later in the manufacturing process of the surface acoustic wave device 1. The pillar portion 2e is incorporated in the sealing portion 4, and the pillar portion 2e and the sealing portion 4 are integrated with the entire surface of the pillar portion 2e covered by the sealing portion 4. The collective substrate 13 on which the device chip 3 is mounted and the sealing portion 4 is formed in this way is diced into regions for each surface acoustic wave device 1, so that a plurality of surface acoustic wave devices 1 are generated.

[0020] The device chip 3 includes a functional element 7 including an IDT electrode 7b (see FIG. 4) at a portion facing the internal space 6 on the functional surface 3a, and includes a resonator 7a in the illustrated example. The device chip 3 has a function of propagating elastic waves. Typically, a piezoelectric material such as lithium tantalate or lithium niobate is used for the device chip 3. Further, the device chip 3 may be configured by laminating these piezoelectric materials on a support such as sapphire, silicon, alumina, spinel, quartz or glass.

[0021] FIG. 4 shows an example of a resonator 7a that becomes a SAW filter. The resonator 7a has an IDT electrode 7b and a reflector 7c formed so as to sandwich the IDT electrode 7b. The IDT electrode 7b is composed of electrode pairs, and each electrode pair is formed by connecting a plurality of electrode fingers 7d arranged in parallel so that the length direction intersects the propagation direction x of the elastic wave at one end side with a bus bar 7e. The reflector 7c is formed by connecting between the ends of a plurality of electrode fingers 7f arranged in parallel so that the length direction intersects the propagation direction x of the elastic wave with a bus bar 7g. Such a resonator 7a is typically composed of a conductive metal film formed by photolithography technology and etching. In the illustrated example, a plurality of such resonators 7a are formed on one device chip 3.

[0022] FIG. 5 shows an example concept of the circuit 11 provided on one device chip 3. Reference numeral 7aa indicates a resonator 7a connected in series between the input / output ports 9, reference numeral 7ab indicates a resonator 7a connected in parallel between the input / output ports 9, reference numeral 12 indicates ground, and reference numeral 8 indicates wiring. The number and arrangement of the resonators 7a are changed as necessary. That is, the circuit 11 in FIG. 5 is configured to form a ladder-type filter.

[0023] In this embodiment, as shown in FIGS. 2 and 3, the package substrate 2 is provided with a plurality of metal pillar portions 2e that protrude from the one surface 2a and are built in the second portion 4b of the sealing portion 4.

[0024] The pillar portion 2e is typically preferably composed of a metal having a high thermal conductivity such as copper or a copper alloy.

[0025] The pillar portion 2e has a base fixed to one surface 2a of the package substrate 2 and protrudes in a direction orthogonal to this one surface 2a. In the illustrated example, the base 2ea of the pillar portion 2e is formed by an end portion located on the one surface 2a of the package substrate 2 in the internal wiring 2ba of the package substrate 2. In the illustrated example, such internal wiring 2ba is connected to the external connection terminal 2d on the other surface 2c side of the package substrate 2.

[0026] A plurality of pillar portions 2e are provided at positions between the outer edge of the package substrate 2 and the side surface 3c of the device chip 3. A gap is provided between the pillar portion 2e and the side surface 3c of the device chip 3, and a gap is also provided between the pillar portion 2e and the outer edge of the package substrate 2. In a state of viewing the elastic wave device 1 from a direction orthogonal to the one surface 2a of the package substrate 2, a gap is also formed between adjacent pillar portions 2e in the circumferential direction y (see FIG. 1) of the device chip 3. In the illustrated example, three pillar portions 2e are incorporated in each of the four side portions 1a of the elastic wave device 1 in the second portion 4b. However, the number of pillar portions 2e incorporated in the second portion 4b, the interval between two adjacent pillar portions 2e as described above, the formation position and arrangement of the pillar portions 2e, etc. may be appropriately changed as required.

[0027] The height of the pillar portion 2e is greater than the distance between the functional surface 3a of the device chip 3 and the one surface 2a of the package substrate 2. The pillar portion 2e is typically configured in the range of a height of 50 to 200 μm and a thickness of 30 to 80 μm. In the illustrated example, the pillar portion 2e has a columnar shape having the base portion 2ea and the protruding end portion 2eb opposite to this base portion 2ea, and the protruding end portion 2eb is positioned at a level between the functional surface 3a and the non-functional surface 3b of the device chip 3. In the illustrated example, the cross section of the pillar portion 2e in a direction orthogonal to the height direction is substantially circular at any position along the height direction. However, such a cross-sectional shape of the pillar portion 2e may be appropriately changed to a polygonal shape or the like as required.

[0028] Also, the contact area between the pillar portion 2e and the sealing portion 4 is three times or more the contact area between the pillar portion 2e and the package substrate 2. That is, the surface area from the base portion 2ea to the protruding end portion 2eb of the pillar portion 2e is three times or more the contact area between the base portion 2ea of the pillar portion 2e and the one surface 2a of the package substrate 2.

[0029] Also, in the illustrated example, it is preferable that the pillar portion 2e be electrically connected to the ground pattern formed on the package substrate 2. In the illustrated example, the internal wiring 2ba of the package substrate 2 having the base portion 2ea of the pillar portion 2e as an end portion becomes all or part of the ground pattern, or is connected to the ground pattern. By doing so, it becomes possible to efficiently radiate the heat transmitted to the pillar portion 2e to the outside by utilizing the ground pattern generally set to widen the width in the direction orthogonal to the signal transmission direction.

[0030] The surface acoustic wave device 1 according to the first example shown in FIGS. 1 to 5 can be reasonably and appropriately formed by the following process. Step 1: Mount the device chip 3 as described above for each region that will become one surface acoustic wave device 1 on the assembly substrate 13 that will become the package substrate 2. Step 2: For each region, form the necessary number of pillar portions 2e on the side of the mounted device chip 3 (see FIG. 6). Specifically, first, a resist layer 14 is formed on the assembly substrate 13. Next, holes 15 having a shape complementary to the pillar portion 2e are formed in the resist layer 14. In the illustrated example, these holes 15 are opened on the surface of the resist layer 14, and the end portions of the internal wiring 2ba are positioned at the bottom of the holes 15. These holes 15 can typically be formed by photolithography technology and etching, or by laser processing (FIG. 6(a)). Next, the holes 15 are filled with a metal that will become the pillar portion 2e by via filling plating, and the holes 15 are filled with this metal to form the pillar portion 2e (FIG. 6(b)). After that, the resist layer 14 is removed with a chemical solution (FIG. 6(c)). Step 3: On one surface of the assembly substrate 13 on which the pillar portion 2e is formed, form the sealing portion 4 so that the pillar portion 2e is built in the sealing portion 4 as described above. Step 4: Cut the assembly substrate 13 on which the sealing portion 4 is formed into pieces for each region by dicing.

[0031] Since the elastic wave device 1 according to this embodiment has the above configuration, the pillar portion 2e can highly secure the mechanical integrity between the sealing portion 4 and the package substrate 2 while efficiently conducting the heat generated in the device chip 3 to the package substrate 2 and releasing it to the outside.

[0032] FIG. 7 shows a second example in which all or a part of the surface of the pillar portion 2e provided in the elastic wave device 1 as described above is made into a rough surface 2ec. By doing so, since the contact area between the sealing portion 4 and the pillar portion 2e increases, further improvement in the mechanical integrity between the sealing portion 4 and the package substrate 2 can be achieved. The surface of the pillar portion 2e can be made into the rough surface 2ec by wet etching or the like. In addition, since the other configurations of this second example are substantially the same as those of the first example, the description thereof is omitted.

[0033] FIG. 8 shows a third example in which the pillar portion 2e provided in the elastic wave device 1 as described above is formed such that its thickness gradually increases as it approaches the protruding end portion 2eb. By doing so, it becomes easier for the pillar portion 2e to resist the force in the direction of separating the package substrate 2 and the sealing portion 4 due to the shape of the pillar portion 2e, and further improvement in the mechanical integrity between the sealing portion 4 and the package substrate 2 can be achieved. Making the pillar portion 2e have such a shape can be achieved by forming a hole 15 having a shape complementary to the pillar portion 2e as shown in FIG. 9(a) in the resist layer 14 formed on the collective substrate 13 described in the process of the first example, and then filling the hole 15 with a metal to become the pillar portion 2e by via filling plating and filling the hole 15 with this metal to form the pillar portion 2e, and then removing the resist layer 14 with a chemical solution as shown in FIG. 9(c). In addition, since the other configurations of this third example are substantially the same as those of the first example, the description thereof is omitted.

[0034] FIG. 10 shows a fourth example in which the protruding end portion 2eb side of the pillar portion 2e provided in the elastic wave device 1 as described above is formed into a head shape. In this example, the side of the pillar portion 2e opposite to the base portion 2ea side has a circumferential stepped surface 2ed facing the base portion 2ea side, and the portion above this circumferential stepped surface 2ed is formed into a head shape that is thicker than the portion below it. By doing so, it becomes easier for the pillar portion 2e to resist the force in the direction of separating the package substrate 2 and the sealing portion 4 due to the shape of the pillar portion 2e, and further improvement in the mechanical integrity between the sealing portion 4 and the package substrate 2 can be achieved. Forming the pillar portion 2e into such a shape can be achieved by forming a hole 15a having a shape complementary to the shape of the protruding end portion 2eb and below of the pillar portion 2e as shown in FIG. 11(a) in the first resist layer 14a formed on the collective substrate 13 described in the process of the first example, and then filling the metal that constitutes the protruding end portion 2eb and below of the pillar portion 2e into the hole 15a by via filling plating as shown in FIG. 9(b) and filling the hole 15a with this metal to form the protruding end portion 2eb and below of the pillar portion 2e. Next, as shown in FIG. 11(c), a second resist layer 14b is formed on the first resist layer 14a, and a hole 15b having a shape complementary to the shape of the protruding end portion 2eb side of the pillar portion 2e is formed in this second resist layer 14b. Then, as shown in FIG. 11(d), the metal that constitutes the protruding end portion 2eb side of the pillar portion 2e is filled into the hole 15b by via filling plating and the hole 15b is filled with this metal to form the protruding end portion 2eb side of the pillar portion 2e. After that, as shown in FIG. 11(e), the first resist layer 14a and the second resist layer 14b are removed by a chemical solution. Note that since the other configurations of this fourth example are substantially the same as those of the first example, the description thereof is omitted.

[0035] Of course, the present invention is not limited to the embodiments described above, and includes all embodiments capable of achieving the object of the present invention.

Description of Reference Numerals

[0036] 1 Elastic wave device 1a Side portion 2 Package substrate 2a One surface 2b Wiring 2ba Internal wiring 2c Other surface 2d External connection terminal 2e Pillar portion 2ea Base portion 2eb Protruding end portion 2ec Rough surface 2ed Circumferential step surface 3 Device chip 3a Functional surface 3b Non-functional surface 3c Side surface 4 Sealing portion 4a First part 4b Second part 5 Gap 6 Internal space 7 Functional element 7a, 7aa, 7ab Resonator 7b IDT electrode 7c Reflector 7d Electrode finger 7e Bus bar 7f Electrode finger 7g Bus bar 8 Wiring 9 Input / output port 10 Protruding electrode 11 Circuit 12 Ground 13 Assembly substrate 14, 14a, 14b Resist layer 15, 15a, 15b Hole x Propagation direction y Circumferential direction

Claims

1. A package substrate, a device chip mounted on the package substrate with a functional surface having a functional element including an IDT electrode facing one surface of the package substrate, a first portion covering a non-functional surface of the device chip facing the functional surface of the device chip, and a second portion following the first portion and covering a side surface having a thickness of the device chip between the functional surface and the non-functional surface and reaching the one surface of the package substrate, and a sealing portion forming an internal space between the functional surface of the device chip and the one surface of the package substrate, An elastic wave device, wherein the package substrate is provided with a plurality of metal pillar portions protruding from the one surface and built in the second portion of the sealing portion.

2. The elastic wave device according to claim 1, wherein an area where the pillar portion and the sealing portion are in contact is three times or more an area where the pillar portion and the package substrate are in contact.

3. The elastic wave device according to claim 1, wherein all or part of a surface of the pillar portion is made into a rough surface.

4. The elastic wave device according to claim 1, wherein the pillar portion is formed such that its thickness gradually increases as it approaches a protruding end portion thereof.

5. The elastic wave device according to claim 1, wherein a protruding end portion side of the pillar portion is formed into a head shape.

6. The elastic wave device according to claim 1, wherein the pillar portion is electrically connected to a ground pattern formed on the package substrate.

7. The elastic wave device according to claim 1, wherein a plurality of the pillar portions are provided with a space therebetween in a direction of going around the device chip in a state of viewing the elastic wave device from a direction orthogonal to the one surface of the package substrate.

8. The elastic wave device according to claim 1, wherein a height of the pillar portion is not made larger than a distance between the functional surface of the device chip and the one surface of the package substrate.

Images