Elastic wave device and manufacturing method for the same

Abstract

To provide an elastic wave device with the electric connection to the outside obtained by a pillar bump, having a suitable and rational structure in which a certain amount of thickness of a fusible part including solder can be secured normally between the device and a pad where the device is to be mounted.SOLUTION: A pillar bump 7 standing on a functional surface 2a of a device chip 2 includes a pillar part 7a including a conductive material and a fusible part 7b including solder S. In the pillar part 7a, an upper part 7d, which is opposite to a base part 7c integrated with the functional surface 2a side, is used as a reception part 7g of the fusible part 7b that is depressed toward the base part 7c so that a ridge part 7f circulating around a center axis x of the pillar part 7a is formed between the upper part and a side part 7e of the pillar part 7a. The fusible part 7b is integrated with the pillar part 7a in such a way that its lower part 7i enters the reception part 7g and its side part is placed outside the ridge part 7f of the pillar part 7a on the lower part 7i.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present invention relates to an acoustic wave device suitable for use as a frequency filter in a mobile communication device or the like, and to a method for manufacturing the same. [Background technology]

[0002] There are bare-chip acoustic wave devices (electronic devices that apply surface acoustic waves / SAW devices) that are configured to be flip-chip mounted using pillar bumps on an aggregate substrate that will become a package substrate or an aggregate substrate that will become a module substrate, and that are electrically connected to the package substrate or the like using pillar bumps.

[0003] The cross-sectional structure is shown in FIG. In FIG. 12, reference numeral 100 denotes a device chip, reference numeral 101 denotes a functional element including an IDT electrode, reference numeral 102 denotes a pad for external connection in wiring connected to the functional element, reference numeral 103 denotes a support layer (wall layer) made of an insulating material formed to surround the functional element, reference numeral 104 denotes a cover layer (roof layer) formed on the support layer to form an internal space above the functional element, reference numeral 105 denotes a via that penetrates the support layer and roof layer and positions the pad at the bottom of the hole, and reference numeral 106 denotes a pillar bump formed in this via 105. The pillar bump has a structure in which solder S is placed on the top of a cylindrical pillar portion 106a, and the two are integrated together. The acoustic wave device configured in this manner is integrated with the pad Pa of the mounting counterpart P by melting and solidifying the solder S while the solder S is pressed against the pad Pa.

[0004] Here, it is known that the thickness of the solder S interposed between the pillar portion 106a and the pad Pa of the mounting counterpart is a factor that has a significant effect on the life of the acoustic wave device. When the acoustic wave device operates, the acoustic wave device becomes hot, and the thermal expansion coefficients of the device chip and the package substrate or module substrate that is the mounting counterpart P are different, so the expansion in the planar direction of each is different. This difference in expansion is absorbed by the solder.

[0005] There are many cases where the thickness of the solder S cannot be sufficiently ensured with conventional pillar bumps 106. Specifically, when the thickness of the solder S between the pillar portion 106a and the pad Pa of the mounting partner P becomes too small (FIG. 13(a)), when the pad Pa of the mounting partner P is tilted and there is a portion where the solder S is not interposed between the pillar portion 106a and the pad Pa of the mounting partner P (FIG. 13(b)), or when the solder S is extruded from between the pillar portion 106a and the pad Pa of the mounting partner P and the two are fixed to each other on the outside by the extruded solder S (FIG. 13(c)), the thickness of the solder S cannot be sufficiently ensured in any of these cases. Summary of the Invention [Problem to be solved by the invention]

[0006] The main problem that this invention aims to solve is how to provide an appropriate and rational structure for an acoustic wave device that is electrically connected to the outside world via pillar bumps, which ensures that the thickness of the weldable portion made of solder between the pad and the mounting surface is always constant. [Means for solving the problem]

[0007] In order to achieve the above object, from a first viewpoint, the present invention provides an acoustic wave device comprising: a device chip having one surface as a functional surface on which a functional element including an IDT electrode is formed; pillar bumps provided upright on the functional surface; and wiring connecting the pillar bumps to the functional element; the pillar bump includes a pillar portion made of a conductive material and a weldable portion made of solder, an upper portion of the pillar portion opposite to the base portion integrated with the functional surface side is recessed toward the base portion side so as to form a ridge portion that goes around the central axis of the pillar portion between the upper portion of the pillar portion and a side portion of the pillar portion, and serves as a receiving portion for the weldable portion; The weldable part is integrated with the pillar part by fitting its lower part into the receiving part and positioning its side part on the lower part outward from the ridge part of the pillar part.

[0008] In one aspect of the present invention, the pillar portion is made of a conductive material other than solder that has a melting point higher than that of solder. Also, in another aspect of the present invention, the pillar portion is made of copper or a copper alloy.

[0009] In order to achieve the above object, from a second aspect, the present invention provides a method for manufacturing an acoustic wave device, comprising: a first step of forming functional elements and wiring on one surface of the wafer for each region of the wafer that will become one of the device chips; a second step of depositing a resist layer on the one side of the wafer; a third step of forming holes for generating the pillar portions in the resist layer at positions where the pillar bumps are to be erected for each region that will become one of the device chips on the wafer; a fourth step of generating the pillar portion by electrolytic plating in the generating hole formed in the third step; a fifth step of removing the resist layer; and a sixth step of forming the weldable portion on an upper portion of the pillar portion, In the fourth step, the electrolytic plating is performed so that the receiving portion is formed on the upper part of the pillar portion, recessed toward its base side so as to form a ridge portion circumnavigating the central axis of the pillar portion between the upper part of the pillar portion and its side portion.

[0010] In this case, in the sixth step, after printing the solder on the receiving portion of the pillar portion, a reflow process is performed to form the weldable portion in a substantially spherical, flattened spherical or substantially spheroidal shape, with the lower portion below the maximum diameter position and inserted into the receiving portion, which is one aspect of this invention. [Effects of the Invention]

[0011] According to this invention, the receiving portion of the pillar portion enables mounting in a state where a constant thickness of the weldable portion made of solder is always ensured between the receiving portion of the pillar portion and the pad of the mounting partner. [Brief explanation of the drawings]

[0012] [Figure 1] FIG. 1 is a plan view showing the configuration of an acoustic wave device (first example) according to an embodiment of the present invention. [Figure 2] FIG. 2 is a cross-sectional view taken along line AA in FIG. [Figure 3] FIG. 3 is an enlarged view of the main part of FIG. [Figure 4] FIG. 4 is a perspective view of the main part of the pillar bump. [Figure 5] FIG. 5 is a diagram showing an example of a configuration of a resonator formed on a device chip that constitutes the acoustic wave device. [Figure 6] FIG. 6 is a configuration diagram showing an example of a circuit formed on a device chip that constitutes the acoustic wave device. [Figure 7] FIG. 7 is a cross-sectional view of the essential part showing the welded state between the pillar bump and the pad on the mounting partner. [Figure 8] FIG. 8 is a cross-sectional view showing a main part of one step in the process of forming the pillar bump. [Figure 9] FIG. 9 is a cross-sectional view showing a main part of a step in the process of forming the pillar bump. [Figure 10]FIG. 10 is a cross-sectional view showing a main part of a step in the process of forming the pillar bump. [Figure 11] FIG. 11 is a cross-sectional view showing a main part of a step in the process of forming the pillar bump. [Figure 12] FIG. 12 is a cross-sectional view of a conventional example. [Figure 13] FIG. 13 is a cross-sectional view of a main part showing the welding state between a conventional pillar bump and a pad on a mounting partner. DETAILED DESCRIPTION OF THE INVENTION

[0013] Exemplary embodiments of the present invention will now be described with reference to Figures 1 to 11. An acoustic wave device 1 according to this embodiment is suitable for use as a frequency filter in mobile communication devices and the like.

[0014] The acoustic wave device 1 according to this embodiment has a configuration in which a device chip 2 is provided with a functional element 3, wiring 4, a support layer 5, a cover layer 6, and pillar bumps 7.

[0015] Furthermore, the pillar bumps 7 of the acoustic wave device 1 are electrically connected to the pads Pa of the mounting counterpart P by flip-chip mounting. That is, the acoustic wave device 1 according to this embodiment is a bare chip.

[0016] One surface of the device chip 2 is a functional surface 2a on which functional elements 3 including IDT electrodes are formed. The pillar bumps 7 are provided upright on the functional surface 2 a of the device chip 2 . Moreover, on the functional surface 2a of the device chip 2, wiring 4 (see FIG. 6) is formed that connects the pillar bumps 7 and the functional elements 3.

[0017] The functional elements 3 and wiring 4 are made of a conductive material, typically a metal film, and are formed into a predetermined pattern using photoresist technology and etching in each region of a wafer (not shown) that will become the device chip 2.

[0018] The support layer 5 is made of an insulating material such as an insulating resin. The thickness of the support layer 5 on the functional surface 2a is made thicker than the thicknesses of the functional elements 3 and the wiring 4. The support layer 5 is formed so as to surround the formation area of ​​the functional elements 3. The support layer 5 is formed as described above by forming the resin layer on one surface of a wafer (not shown) for each area that will become the device chip 2, and then using photoresist technology and etching.

[0019] The cover layer 6 is made of an insulating material such as an insulating resin. One surface of the cover layer 6 is fixed to the upper surface 5a of the support layer 5, and the cover layer 6 is supported by the support layer 5, so as to form an internal space 8 between the cover layer 6 and the support layer 5, sealing the functional element 3. The cover layer 6 is typically formed by placing a film constituting the cover layer 6 on the wafer on which the support layer 5 is formed, and then fixing the film to the support layer 5.

[0020] The pillar bump 7 protrudes in a direction perpendicular to the functional surface 2a. The pillar bump 7 includes a pillar portion 7a made of a conductive material and a weldable portion 7b made of solder S.

[0021] The pillar portion 7a is made of a conductive material other than solder S, which has a melting point higher than that of solder S. Considering availability, integration with solder S, conductivity, ease of production by electrolytic plating (described later), etc., it is preferable that the pillar portion 7a be made of copper or a copper alloy. In the illustrated example, pads 4a constituting part of the wiring 4 are formed at the four corners of the device chip 2, and corresponding pillar bumps 7 are erected at the four corners of the device chip 2. The number and erect positions of the pillar bumps 7 may be changed as needed. At the position where the pillar bump 7 is provided, a via 9 is formed which penetrates the support layer 5 and the cover layer 6 and positions the pad Pa at the bottom of the hole.

[0022] The pillar portion 7a has an upper portion 7d opposite to a base portion 7c integrated with the functional surface 2a via a pad 4a, which is recessed toward the base portion 7c so as to form a ridge portion 7f that circles the central axis x (see Figures 3 and 4) of the pillar portion 7a between the upper portion 7d and the side portion 7e of the pillar portion 7a, thereby serving as a receiving portion 7g for the weldable portion 7b. In the illustrated example, the pillar portion 7a has a cylindrical shape. The receiving portion 7g has a substantially circular or elliptical cross-sectional internal shape in a direction perpendicular to the central axis x at any position from the bottom 7h of the receiving portion 7g to the ridge portion 7f, and the inner diameter gradually increases from the bottom 7h to the ridge portion 7f.

[0023] On the other hand, the weldable portion 7b is substantially spherical, or flattened spherical, or substantially spheroidal. The lower portion 7i of the weldable portion 7b fits snugly into the receiving portion 7g, and has a three-dimensional shape that is complementary to the internal space of the receiving portion 7g. The weldable portion 7b has a lower portion 7i below its maximum diameter position (see FIG. 3), and this lower portion 7i is fitted into the receiving portion 7g. Therefore, the pillar bump 7 has a shape having an eave-shaped portion (see FIG. 3) that surrounds the central axis x due to the weldable portion 7b.

[0024] That is, the weldable portion 7b is integrated with the pillar portion 7a by inserting its lower portion 7i into the receiving portion 7g and positioning its side portion (maximum diameter position 7j) on the lower portion 7i outward from the ridge portion 7f of the pillar portion 7a (Figure 3).

[0025] The acoustic wave device 1 configured in this manner is integrated with the pad Pa of the mounting partner P by melting and solidifying the solder S while the weldable portion 7b is pressed against the pad Pa. Here, it is known that the thickness of the solder S interposed between the pillar portion 7 a and the pad Pa of the mounting counterpart P is a factor that has a significant effect on the life of the acoustic wave device 1 . The operation of the acoustic wave device 1 causes the acoustic wave device 1 to reach a high temperature, and since the thermal expansion coefficients of the device chip 2 and the package substrate or module substrate serving as the mounting counterpart P are different, the expansion in the planar direction of each device differs. This difference in expansion is absorbed by the solder S. In the elastic wave device 1 of this embodiment, the receiving portion 7g of the pillar portion 7a makes it possible to mount the device in a state where the thickness of the weldable portion 7b made of solder S is always maintained at a constant amount between the pad Pa of the mounting partner P. Specifically, it is possible to ensure sufficient thickness of the solder S in any of the following cases: a typical case (Figure 7(a)), a case where the pad Pa of the mounting counterpart P is inclined (Figure 7(b)), or a case where a large amount of solder S is extruded from between the pillar portion 7a and the pad Pa of the mounting counterpart P (Figure 7(c)).

[0026] Typically, the device chip 2 is configured as a rectangular plate with sides of 0.5 to 1 mm and a thickness of 0.15 to 0.2 mm. The support layer 5 has a thickness of 20 to 30 μm. The cover layer 6 has a thickness of 20 to 30 μm. The pillar bumps 7 have a height of 50 to 80 μm. The acoustic wave device 1 configured from these has a thickness of approximately 0.25 to 0.3 mm. Typically, the acoustic wave device 1 has a hexahedral shape with rectangular opposite surfaces and four thick side surfaces.

[0027] The device chip 2 has a function of propagating elastic waves. A piezoelectric material such as lithium tantalate or lithium niobate is typically used for the device chip 2. The device chip 2 may also be configured by laminating these piezoelectric materials on a support such as sapphire, silicon, alumina, spinel, quartz, or glass.

[0028] Figure 5 shows an example of a resonator 3a serving as a SAW filter. The resonator 3a has an IDT electrode 3b and a reflector 3c formed on either side of the IDT electrode 3b. The IDT electrode 3b consists of an electrode pair, and each electrode pair has multiple electrode fingers 3d arranged in parallel so that their length direction intersects the propagation direction y of the acoustic wave, and each electrode pair has one end connected to the other by a busbar 3e. The reflector 3c has multiple electrode fingers 3f arranged in parallel so that their length direction intersects the propagation direction y of the acoustic wave, and each electrode finger 3d has one end connected to the other by a busbar 3g. In the illustrated example, a plurality of such resonators 3 a are formed on one device chip 2 .

[0029] Figure 6 shows the concept of an example of a circuit 10 provided on one device chip 2. Reference numeral 3aa denotes resonators 3a connected in series between input and output ports 11, reference numeral 3ab denotes resonators 3a connected in parallel between input and output ports 11, and reference numeral 12 denotes a ground. The number and arrangement of the resonators 3a can be changed as needed. In other words, a ladder-type filter is configured by the circuit 10 of Figure 6.

[0030] The acoustic wave device 1 described above can be formed rationally and appropriately by the following process.

[0031] First step: In each area of ​​the wafer 13 that will become one device chip 2, functional elements 3 and wiring 4 are formed on one surface by photolithography and etching. These are made of a conductive metal film, and are typically set to a thickness in the range of 0.2 to 0.4 μm.

[0032] Second step: A resist layer 14 is formed on the one surface of the wafer 13 (FIG. 8). The thickness of the resist layer 14 is set to be substantially equal to the height of the pillar portions 7a.

[0033] Third step: A hole 15 for generating the pillar portion 7a is formed in the resist layer 14 at a position where the pillar bump 7 is to be erected for each region that will become one of the device chips 2 on the wafer 13 (FIG. 9). The hole 15 for generating the pillar portion 7a can be formed by applying photolithography and etching to the resist layer 14.

[0034] Fourth step: The pillar portions 7a are formed in the forming holes 15 formed in the third step by electrolytic plating (FIG. 10). In this fourth step, the electrolytic plating is performed so that the receiving portion 7g is formed on the upper portion 7d of the pillar portion 7a, recessed toward the base portion 7c so as to form a ridge portion 7f that circumnavigates the central axis x of the pillar portion 7a between the upper portion 7d and the side portion 7e. Specifically, the plating bath time, the concentration of additives (accelerators, retarders) in the plating solution, etc. are adjusted so that pillar portions 7a having the above-described shape are formed.

[0035] Fifth step: The resist layer 14 is removed with a chemical (FIG. 11).

[0036] Sixth step: The weldable portion 7b is formed on the upper portion 7d of the pillar portion 7a. In this sixth step, the solder S is printed on the receiving portion 7g of the pillar portion 7a, and then a reflow process is performed to form the weldable portion 7b in a substantially spherical, flattened spherical, or substantially spheroidal shape, with the lower portion 7i below the maximum diameter position 7j being inserted into the receiving portion 7g. Specifically, the amount of solder S placed on the receiving portion 7g is adjusted. The solder S melted by the reflow process becomes substantially spherical, flattened spherical, or substantially spheroidal due to surface tension, forming a hood-like portion orbiting the central axis x. This allows the pillar bump 7 to hold the weldable portion 7b made of a sufficient amount of solder S.

[0037] Thereafter, a support layer 5 and a cover layer 6 are formed on the wafer 13, and the wafer is further cut into regions that become device chips 2 by dicing, so that a plurality of acoustic wave devices 1 are produced from one wafer 13.

[0038] It should be noted that the present invention is not limited to the above-described embodiments, but includes all embodiments that can achieve the object of the present invention. [Explanation of symbols]

[0039] 1. Acoustic wave devices 2. Device chip 2a Functional aspect 3 Functional elements 3a, 3aa, 3ab resonators 3b IDT electrode 3c reflector 3d electrode fingers 3e Busbar 3f electrode finger 3g busbar 4 Wiring 4a pad 5 Support layer 5a Top side 6 Cover Layer 7 Pillar Bump 7a Pillar section 7b Weldable area 7c base 7d top 7e side 7f ridge 7g Receiving part 7h bottom 7i lower 7j Maximum diameter position 7k eaves 8. Interior Space 9 Via 10 circuits 11 Input / Output Ports 12 grand 13 wafers 14 Resist layer 15 Generating hole P Implementation partner Pa Pad S solder x center axis

Claims

1. a device chip having a functional surface on one side of which a functional element including an IDT electrode is formed, pillar bumps being provided upright on the functional surface, and wiring connecting the pillar bumps to the functional element; the pillar bump includes a pillar portion made of a conductive material and a weldable portion made of solder, an upper portion of the pillar portion opposite to the base portion integrated with the functional surface side is recessed toward the base portion side so as to form a ridge portion that goes around the central axis of the pillar portion between the upper portion of the pillar portion and a side portion of the pillar portion, and serves as a receiving portion for the weldable portion; The weldable portion is integrated with the pillar portion by inserting its lower portion into the receiving portion and positioning its side portion on the lower portion outward from the ridge portion of the pillar portion.

2. 2. The acoustic wave device according to claim 1, wherein the pillar portion is made of a conductive material other than solder, the conductive material having a melting point higher than that of solder.

3. The acoustic wave device according to claim 1 , wherein the pillar portion is made of copper or a copper alloy.

4. a first step of forming functional elements and wiring on one surface of the wafer for each region of the wafer that will become one of the device chips; a second step of depositing a resist layer on the one side of the wafer; a third step of forming holes for generating the pillar portions in the resist layer at positions where the pillar bumps are to be erected for each region that will become one of the device chips on the wafer; a fourth step of generating the pillar portion by electrolytic plating in the generating hole formed in the third step; a fifth step of removing the resist layer; and a sixth step of forming the weldable portion on an upper portion of the pillar portion, In the fourth step, the electrolytic plating is performed so that the receiving portion is formed on the top of the pillar portion, recessed toward its base side so as to form a ridge portion between the top and side of the pillar portion that circumvents the central axis of the pillar portion.

5. 5. The method for manufacturing an acoustic wave device according to claim 4, wherein in the sixth step, the solder is printed on the receiving portion of the pillar portion, and then a reflow process is performed to form the weldable portion in a substantially spherical, oblate spherical, or substantially spheroidal shape, with the lower portion below a maximum diameter position and the lower portion inserted into the receiving portion.

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