Elastic wave device

Abstract

To provide a new structure that can rationally improve a heat dissipation in an elastic wave device of a wafer level package (WLP) structure.SOLUTION: An elastic wave device comprises: a roof substrate 6 that is bonded onto a thick film wiring 4 and a surrounded metal layer 5, and forms a sealing space 10 for hermetically sealing a function element 3 so as to be cooperated with a device chip 2 and the surrounded metal layer 5; a connection bump 7 having an internal end 7a that is formed into a passing hole 2f penetrated to the device chip 2, and is fastened to the thick film wiring 4, and an external end 7b to be positioned to an outside of the other surface 2b of the device chip 2; a heat dissipation layer 8 that is formed to the other surface 2b of the device chip 2; and a heat dissipation bump 9 that is formed onto the heat dissipation layer 8.SELECTED DRAWING: Figure 1

Description

Technical Field

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

Background Art

[0002] As an elastic wave (Surface Acoustic Wave / SAW) device having a WLP (Wafer Level Package) structure, there is one disclosed in Patent Document 1. The device of this Patent Document 1 has a functional element on one surface of a piezoelectric substrate (device chip), a support portion surrounding the formation region of this functional element, and a cover portion that cooperates with the support portion to form a sealing space for the functional element. The functional element is connected to the outside via a through electrode penetrating the piezoelectric substrate.

[0003] Here, in this type of elastic wave device, improvement of heat dissipation is strongly demanded.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] The main problem to be solved by this invention is to provide a new structure capable of reasonably improving heat dissipation in this type of elastic wave device having a WLP structure.

Means for Solving the Problems

[0006] In order to achieve the above object, in this invention, the elastic wave device is A device chip comprising: a plurality of functional elements including at least IDT electrodes on one surface; a thick film wiring having a greater thickness than the functional elements; and a surrounding metal layer that surrounds the formation regions of the functional elements and the thick film wiring and has the same thickness as the thick film wiring. A roof substrate that is located on and supported by the thick film wiring and the surrounding metal layer, and forms a sealing space that cooperates with the device chip and the surrounding metal layer to hermetically seal the functional elements. A connection bump formed in a through hole penetrating the device chip, having an inner end fixed to the thick film wiring, and an outer end located outside the other surface of the device chip. A heat dissipation layer formed on the other surface of the device chip. A heat dissipation bump formed on the heat dissipation layer.

[0007] One aspect of the present invention is to configure the roof substrate from high-resistance silicon, ceramic, or glass. In this case, another aspect of the present invention is to make the thickness of the device chip smaller than the thickness of the roof substrate.

[0008] Also, in a state where the elastic wave device is viewed from a direction orthogonal to the one surface and the other surface of the device chip, one aspect of the present invention is to form the heat dissipation layer such that at least a part of the formation region of the heat dissipation layer is located directly above or directly below the formation region of the functional element.

Advantages of the Invention

[0009] According to the present invention, the elastic wave device can be mounted on a module substrate by using the connection bump to orient the other surface of the device chip toward the mounting surface of the module substrate. Heat generated in the formation region of the functional element in the device chip can be transferred to the module substrate side by forming the shortest heat dissipation path through the heat dissipation layer and the heat dissipation bump formed thereon.

Brief Description of the Drawings

[0010]

Figure 1

Figure 2

Figure 3

Figure 4

DETAILED DESCRIPTION OF THE INVENTION

[0011] Hereinafter, based on FIGS. 1 to 4, typical embodiments of the present invention will be described. The elastic wave device 1 according to this embodiment is suitable for use as a frequency filter or the like in mobile communication devices or the like.

[0012] Such an elastic wave device 1 includes a device chip 2, a functional element 3, a thick film wiring 4, a surrounding metal layer 5, a roof substrate 6, a connection bump 7, a heat dissipation layer 8, and a heat dissipation bump 9.

[0013] A functional element 3 is formed on one surface 2a of the device chip 2. Also, on one surface 2a of the device chip 2, a thick film wiring 4 and a surrounding metal layer 5 are formed, which increase the thickness in the direction x orthogonal to one surface 2a and the other surface 2b of the device chip 2 more than the functional element 3. The thicknesses of the thick film wiring 4 and the surrounding metal layer 5 are equal.

[0014] The surrounding metal layer 5 is formed slightly inward from the outer edge 2d of the device chip 2 where the one surface 2a and the side surface 2c of the device chip 2 meet. The surrounding metal layer 5 has a rectangular frame shape when viewed from a direction x perpendicular to the one surface 2a and the other surface 2b of the device chip 2. The region inside the surrounding metal layer 5 on the one surface 2a of the device chip 2 forms the main surface 2e of the device chip 2 (the surface that functions as the acoustic wave device 1).

[0015] A plurality of functional elements 3 are formed on the main surface 2 e of the device chip 2 .

[0016] The thick film wiring 4 is formed at a desired position, such as between adjacent functional elements 3, on the main surface 2e of the device chip 2. The thick film wiring 4 is connected to the functional elements 3 via thin film wiring (not shown) or the like.

[0017] The roof substrate 6 is placed on the thick film wiring 4 and the surrounding metal layer 5 and is supported by the thick film wiring 4 and the surrounding metal layer 5 with its inner surface 6 a facing one surface 2 a of the device chip 2 .

[0018] On one surface 2a of the device chip 2, a sealed space 10 (cavity, hollow structure) is formed by the main surface portion 2e, the surrounding metal layer 5, and the roof substrate 6, and a resonator 3a (described later) that constitutes the functional element 3 is arranged within this sealed space 10. The thick film wiring 4 also functions as a spacer that supports the roof substrate 6 within the sealed space 10 .

[0019] The heat dissipation layer 8 is formed on the other surface 2b opposite to the one surface 2a of the device chip 2. The heat dissipation layer 8 is formed so as to cover at least a part of the other surface 2b.

[0020] Typically, the device chip 2 is configured in the shape of a quadrangular (rectangular in the illustrated example) plate with a side measuring 0.5 to 1 mm and a thickness of 0.02 mm (20 μm) to 0.1 mm (100 μm). Also, typically, the functional element 3 is configured such that the thickness in the direction x orthogonal to one surface 2a and the other surface 2b of the device chip 2 (the height of the functional element 3 with respect to one surface 2a of the device chip 2) is 0.1 to 0.5 μm. Also, typically, the thick film wiring 4 and the surrounding metal layer 5 are configured such that the thickness in the direction x orthogonal to one surface 2a and the other surface 2b of the device chip 2 is 3 to 6 μm. Also, typically, the roof substrate 6 is configured such that the thickness is 100 to 150 μm. Also, typically, the heat dissipation layer 8 is configured such that the thickness is 1 to 30 μm. The surface acoustic wave device 1 composed of these typically has a thickness of about 150 to 250 μm.

[0021] Such a surface acoustic wave device 1 has a square or rectangular quadrilateral contour when viewed from the direction x orthogonal to one surface 2a and the other surface 2b of the device chip 2. That is, such a surface acoustic wave device 1 exhibits a flat hexahedron shape including two quadrilateral surfaces 1a and four side surfaces 1b extending between these two surfaces 1a. In each figure, the thickness of the components is exaggerated to facilitate understanding of the configuration of the surface acoustic wave device 1.

[0022] The device chip 2 has a function of propagating surface acoustic waves. Typically, lithium tantalate or lithium niobate is used as the piezoelectric material for the device chip 2, and the device chip 2 may also be configured by laminating sapphire, silicon, alumina, spinel, quartz or glass, etc. on these.

[0023] Fig. 3 shows an example of the configuration of the resonator 3a as the functional element 3. The resonator 3a has an IDT electrode 3b and a reflector 3c formed so as to sandwich the IDT electrode 3b. The IDT electrode 3b consists of electrode pairs, and each electrode pair is formed by connecting a plurality of electrode fingers 3d arranged in parallel so that their length directions cross the propagation direction y of the elastic wave at one end side thereof with a bus bar 3e. The reflector 3c is formed by connecting between the ends of a plurality of electrode fingers 3f arranged in parallel so that their length directions cross the propagation direction y of the elastic wave with a bus bar 3g. The functional element 3 is typically composed of a conductive metal film formed using photolithography technology and etching.

[0024] As shown in FIGS. 1 and 2, the thick film wiring 4 and the surrounding metal layer 5 are formed on the one surface 2a of the device chip 2 and are formed to have a predetermined thickness larger than that of the functional element 3 at any position. In the illustrated example, a part of the pressure film wiring 4 is integrated with the surrounding metal layer 5, and the surrounding metal layer 5 functions as a part of the wiring 12 connected to the ground 13 described later. In the illustrated example, bump pads 14 are formed by the thick film wiring 4 at the four corners of the device chip 2, respectively. Such thick film wiring 4 and surrounding metal layer 5 are also typically composed of a conductive metal film formed using photolithography technology and etching.

[0025] Fig. 4 shows an example concept of a circuit 11 provided on one device chip 2 by the functional element 3, a thin film wiring (not shown), and the thick film wiring 4. Reference numeral 3aa denotes a resonator 3a connected in series between signal input / output terminals 11a, reference numeral 3ab denotes a resonator 3a connected in parallel between signal input / output terminals 11a, and reference numeral 13 denotes the ground. The number and arrangement of the resonators 3a are changed as required. That is, a ladder type filter is configured by the circuit 11 in Fig. 4.

[0026] The roof substrate 6 has an inner surface 6a and an outer surface 6b that are substantially parallel to one surface 2a of the device chip 2. In the illustrated example, the roof substrate 6 has a plate shape with substantially the same shape and size as the device chip 2. A gap corresponding to the thicknesses of the thick film wiring 4 and the surrounding metal layer 5 is formed between the inner surface 6a of the roof substrate 6 and one surface 2a of the device chip 2, and this gap is hermetically sealed by the roof substrate 6 to form the sealing space 10.

[0027] The roof substrate 6 is preferably made of high-resistance silicon, ceramic, or glass. The roof substrate 6, the thick film wiring 4, and the surrounding metal layer 5 are fixed by a known fixing method. When the roof substrate 6 is made of high-resistance silicon, ceramic, or glass as described above, the roof substrate 6, the thick film wiring 4, and the surrounding metal layer 5 can be joined by interposing a thin film layer 15 made of an insulating material or a high-resistance material therebetween. Such a thin film layer 15 is typically formed on the thick film wiring 4 and the surrounding metal layer 5 by sputtering. Specifically, the surface roughness of both the surface of the thin film layer 15 in contact with the roof substrate 6 and the inner surface 6a of the roof substrate 6 in contact with the thin film layer 15 is set to be not less than Ra0.0001 nm and not more than 0.5 nm. In this way, in the manufacturing process of the elastic wave device 1, from the state where an assembly substrate (not shown) serving as the roof substrate 6 is laminated on one surface of a wafer (not shown) serving as the device chip 2, by pressing with a predetermined force, the thin film layer 15 and the assembly substrate serving as the roof substrate 6 can be directly joined.

[0028] The connection bump 7 is formed in a through hole 2f (via) that penetrates the device chip 2 in the direction x orthogonal to one surface 2a and the other surface 2b, and includes an inner end 7a fixed to the thick film wiring 4 and an outer end 7b located outside the other surface 2b of the device chip 2. In the illustrated example, through-holes 2f are formed at the four corners of the device chip 2, with the bump pads 14 positioned at the bottom of the holes. Connection bumps 7 made of a conductive material are formed within these through-holes 2f. The through-holes 2f are typically formed by dry etching. In the illustrated example, the through-holes 2f have the largest hole diameter on the other surface 2b side of the device chip 2 and are configured to gradually decrease in hole diameter as they approach the one surface 2a side of the device chip 2, and the hole openings on this one surface 2a side are blocked by the bump pads 14. The connection bumps 7 are formed by filling the through-holes 2f with a conductive material without any gaps and have a hemispherical head on the other surface 2b of the device chip 2. The surface acoustic wave device 1 is mounted on a support substrate P such as a module substrate by utilizing the outer ends 7b of the connection bumps 7. That is, the surface acoustic wave device 1 is mounted on the support substrate P by fixing the outer ends 7b of the connection bumps 7 to the terminals Pa formed on the support substrate P by ultrasonic welding or the like.

[0029] The heat dissipation layer 8 is composed of a material with high thermal conductivity and a material on which the heat dissipation bumps 9 described later can be formed. Typically, the heat dissipation layer 8 is composed of a metal or a high heat dissipation resin (high thermal conductivity resin). As the high heat dissipation resin, typically, a resin in which a filler made of a substance with high thermal conductivity is contained in the range of 70 wt% to 90 wt% with respect to the base resin is used. Such a filler is typically configured as a granular body with a diameter of around 10 μm. Specifically, as the high heat dissipation resin, an epoxy resin containing a filler or a phenolic resin containing a filler can be used. As the filler, typically, silica, alumina, or aluminum nitride can be used.

[0030] Also, the heat dissipation layer 8 is formed such that at least a part of the formation region of the heat dissipation layer 8 is positioned directly above or below the formation region of the functional element 3 in a state where the surface acoustic wave device 1 is viewed from the direction x orthogonal to the one surface 2a and the other surface 2b of the device chip 2.

[0031] Typically, such a heat dissipation layer 8 is formed by applying a resin to be the heat dissipation layer 8 on the surface opposite to the surface on which the functional element 3 is formed in a wafer (not shown) to be the device chip 2 in the manufacturing process of the surface acoustic wave device 1. Alternatively, such a heat dissipation layer 8 is formed by laminating a film made of a resin to be the heat dissipation layer 8 on the surface opposite to the surface on which the functional element 3 is formed in the wafer 13 to be the device chip 2 in the manufacturing process of the surface acoustic wave device 1, and patterning this film by etching or the like.

[0032] The heat dissipation bump 9 is composed of a material having a high thermal conductivity. Typically, the heat dissipation bump 9 is composed of solder, Cu, Ni, or the like. The heat dissipation bump 9 is formed to have a height that abuts against the support substrate P when the surface acoustic wave device 1 is mounted on the support substrate P using the connection bump 7 (see FIG. 1). In the illustrated example, the heat dissipation bump 9 has a substantially circular cross-section along the one surface 2a and the other surface 2b of the device chip 2 at any position in the protruding direction. Further, the heat dissipation bump 9 is formed such that the cross-sectional area in the cross-section gradually decreases from the base 9a fixed to the heat dissipation layer 8 toward the protruding end 9b thereof, and exhibits a dome shape. In the illustrated example, the surface acoustic wave device 1 is mounted on the support substrate P by fixing the protruding end 9b of the heat dissipation bump 9 to the heat dissipation terminal Pb formed on the support substrate P by ultrasonic welding or the like. A heat dissipation layer 8 is always positioned between the heat dissipation bump 9 and the other surface 2b of the device chip 2. In the illustrated example, the entire region positioned directly below the formation region of the functional element 3 on the other surface 2b of the device chip 2 is covered by the heat dissipation layer 8 (see FIGS. 1 and 2).

[0033] The elastic wave device 1 having the above configuration can be mounted on the support substrate P by using the connection bump 7 so that the other surface of the device chip 2 faces the mounting surface Pc of the support substrate P. The heat generated in the formation region of the functional element 3 in the device chip 2 can be transmitted to the support substrate P side by forming the shortest heat dissipation path z (see FIG. 1) by the heat dissipation layer 8 and the heat dissipation bump 9 formed thereon.

[0034] When the roof substrate 6 is made of high-resistance silicon, ceramic or glass, the rigidity of the elastic wave device 1 can be effectively increased. As a result, the thickness of the device chip 2 can be made as small as possible, that is, thin. That is, even if the thickness of the device chip 2 is made as small as possible, when the elastic wave device 1 as a whole is mounted on the support substrate P together with other devices to form a module, a certain resistance to the molding pressure of the sealing resin formed on the support substrate P can be imparted. Specifically, in the manufacturing process of the elastic wave device 1, from the state where an assembly substrate (not shown) that will become the roof substrate 6 is laminated on one surface of a wafer (not shown) that will become the device chip 2, the other surface side of the wafer can be appropriately thinned by using the rigidity of this assembly substrate to finally produce the device chip 2 of the elastic wave device 1. Specifically, it is one of the preferred embodiments to make the thickness of the device chip 2 smaller than the thickness of the roof substrate 6. As a result, the thickness of the device chip 2 that forms part of the heat dissipation path z can be made as small as possible to shorten the heat dissipation path z, and the heat dissipation efficiency of the heat can be reasonably improved by this shortening. In addition, it becomes easier to form the through hole 2f of the connection bump 7 for the device chip 2.

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

Explanation of Reference Numerals

[0036] 1 Elastic wave device 1a Surface 1b Side surface 2 Device chip 2a One surface 2b The other surface 2c Side surface 2d Outer edge 2e Main surface 2f Through hole 3 Functional element 3a, 3aa, 3ab Resonator 3b IDT electrode 3c Reflector 3d Electrode finger 3e Bus bar 3f Electrode finger 3g Bus bar 4 Thick film wiring 5 Surrounding metal layer 6 Roof substrate 6a Inner surface 6b Outer surface 7 Connection bump 7a Inner end 7b Outer end 8 Heat dissipation layer 9 Heat dissipation bump 9a Base 9b Protruding end 10 Sealing space 11 Circuit 11a Signal input / output terminal 12 Wiring 13 Ground 14 Bump pad 15 Thin film layer P Support substrate Pa Terminal Pb Heat dissipation terminal Pc Mounting surface x Orthogonal direction y Propagation direction z Heat dissipation path

Claims

1. A device chip comprising: a plurality of functional elements including at least IDT electrodes on one surface; a thick film wiring having a greater thickness than the functional elements; and a surrounding metal layer that surrounds the formation regions of the functional elements and the thick film wiring and has the same thickness as the thick film wiring; A roof substrate that is located on and supported by the thick film wiring and the surrounding metal layer and forms a sealing space that cooperates with the device chip and the surrounding metal layer to hermetically seal the functional elements; A connection bump formed in a through hole penetrating the device chip and having an inner end fixed to the thick film wiring and an outer end located outside the other surface of the device chip; A heat dissipation layer formed on the other surface of the device chip; An elastic wave device comprising a heat dissipation bump formed on the heat dissipation layer.

2. The elastic wave device according to claim 1, wherein the roof substrate is made of high-resistance silicon, ceramic, or glass.

3. The elastic wave device according to claim 2, wherein the thickness of the device chip is made smaller than the thickness of the roof substrate.

4. The elastic wave device according to claim 1, wherein at least a part of the formation region of the heat dissipation layer is located directly above or directly below the formation region of the functional element in a state where the elastic wave device is viewed from a direction orthogonal to the one surface and the other surface of the device chip.

Images