JPH08316778A - Mount structure for surface acoustic wave - Google Patents

Abstract

PURPOSE: To obtain the mount structure of the surface acoustic wave device with a structure by which a printed circuit board processed with recess especially is not required and a middle position of a surface acoustic wave propagation path of the surface acoustic wave device is connected to the printed circuit board. CONSTITUTION: A function side 1a of a device chip 1 forming a surface acoustic wave propagation path 4 is opposite to a mount side of a printed circuit board 5 on which components are mounted, and a vibration space is kept between the function side 1a and the mount side and the surrounding of the device chip 1 is coated by a sealing resin 9. In the mount structure of the surface acoustic wave device, a photo resist film 10 surrounding the surface acoustic wave propagation path 4 and lower than the height of the mount bump 6 of the surface acoustic wave propagation path 4 is formed to the function side 1a and a very small gap is formed between the mount side and the front side of the photo resist film 10 while the mount bump 6 is connected to a conductor layer 5a of the printed circuit board 5 and the sealing resin is terminated at the position of the photo resist film 10.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a surface acoustic wave device used as a surface acoustic wave filter or the like, and more particularly to a mounting structure of a surface acoustic wave device of a type mounted on a circuit board by face down bonding.

[0002]

2. Description of the Related Art As is well known, a surface acoustic wave device used as a surface acoustic wave filter or the like has a structure as shown in FIG. That is, for example, the surface wave propagation path 4A is formed on the functional surface 1a of the device chip 1A made of ceramic by the paired comb-teeth-shaped electrodes 2A and 3A for connection with a circuit board such as a printed wiring board 5A. The mounting bumps 6A are arranged at the ends of the comb-shaped electrodes 2A and 3A.

In order to mount the surface acoustic wave device having such a structure on the printed wiring board 5A, as shown in FIG. 5, the functional surface 1a is opposed to the printed wiring board 5A and the surface acoustic wave device is Although the mounting bump 6A is connected to the conductive layer 5a of the printed wiring board 5A,
A recess 7A is formed in the surface wave propagation path corresponding portion of the printed wiring board 5A to form a cavity 8A which allows the vibration of the functional surface 1a to prevent invasion of moisture or dust into the functional surface 1a. The sealing resin 9A is applied to the periphery of the device chip 1A and hermetically sealed.

[0004]

However, according to the conventional surface acoustic wave device mounting structure as described above, the recess 7A is specially formed on the surface of the printed wiring board 5A for mounting the surface acoustic wave device. It is necessary to provide a special printed wiring board 5A according to the mounting position of the surface acoustic wave device and the size of the surface acoustic wave device.
Therefore, it is difficult to cope with the size change of the surface acoustic wave device and the pattern change of the circuit board.

Further, in the same mounting structure, since the central portion of the surface acoustic wave propagation path 4A of the surface acoustic wave device corresponds to the central portion of the recess 7A, the mounting bump 6A should be arranged at the central portion of the surface acoustic wave propagation path 4A. Is impossible, and for this reason, the design pattern of the surface acoustic wave device is limited, and it may be difficult to design the surface acoustic wave device.

In view of the problems of the conventional mounting structure of a surface acoustic wave device as described above, the object of the present invention is to eliminate the need to use a circuit board having a special recess, and to improve the surface of the surface acoustic wave device. To obtain a mounting structure of a surface acoustic wave device having a structure capable of connecting a central portion of a wave propagation path to a circuit board.

[0007]

In order to achieve this object, the present invention has a functional surface of a device chip forming a surface wave propagation path facing a mounting surface of a circuit board to be mounted,
In a mounting structure of a surface acoustic wave device in which a vibrating space is maintained between the functional surface and the mounting surface, the periphery of a device chip is covered with a sealing resin, and the surface wave propagation path is surrounded and the surface wave is surrounded. A photoresist film lower than the mounting bumps of the propagation path is formed on the functional surface, and with the mounting bumps connected to the conductive layer of the circuit board, there is a slight gap between the surface of the photoresist film and the mounting surface. The mounting structure of the surface acoustic wave device in which the gap is formed and the sealing resin is terminated at the position of the photoresist film is proposed. Further, in a preferred embodiment of the present invention described below, the photoresist coating described above is formed in a continuous frame shape surrounding the surface wave propagation path,
Disclosed is a resist film formed of a discontinuous dot or linear resist film surrounding the surface wave propagation path.

[0008]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The details of the embodiments of the present invention will be described below with reference to FIGS. 1 and 2 show a first embodiment of the present invention, in which a surface acoustic wave device as shown in FIG. 1 is used. That is, a surface wave propagation path 4 is formed by a pair of comb-shaped electrodes 2 and 3 on a functional surface 1a of a device chip 1 made of, for example, ceramic, and bonding of end portions of the comb-shaped electrodes 2 and 3 is performed. The pads 2a and 3a have mounting bumps 6 having a height h1 (shown in FIG. 2) for connection with a circuit board such as a printed wiring board 5.
Are arranged by a known forming method.

Further, the functional surface 1a of the device chip 1
A photoresist film 10 having a height h2 in the shape of a continuous rectangular frame surrounding the surface wave propagation path 4 is formed by a photoresist method using, for example, a photosensitive polyimide resin capable of forming a thick layer. As shown in FIG. 2, the height h2 of the photoresist coating 10 is set so that when the mounting bumps 6 of the surface acoustic wave device are connected to the conductive layer 5a of the printed wiring board 5, which is a circuit board, the printed wiring board 5 has a height h2. For the purpose of forming a slight gap with the surface, the height is selected to be equal to or smaller than the height h1 of the mounting bumps 6. As will be understood later, the photoresist film 10 described above blocks the inflow of the sealing resin 9 to form the cavity 8 between the functional surface 1a of the device chip 1 and the mounting surface of the printed wiring board 5. Since it is the purpose, it is not always necessary to form it in a continuous frame shape, and it may be, for example, a dot-shaped or linear photoresist film arranged along a frame-shaped virtual pitch line.

FIG. 2 shows a state in which the device chip 1 is mounted and sealed on the printed wiring board 5 using the above-described surface acoustic wave device. As can be understood from this figure, in this mounting step, the device chip 1 is mounted. The functional surface 1a of the conductive layer 5a
A face-down bonding method is used which faces the mounting surface of the printed wiring board 5 on which is formed. That is, the corresponding mounting bumps 6 of the device chip 1 are connected to the respective conductive layers 5a of the printed wiring board 5 by solder, a conductive resin, or the like, and thereafter, a liquid known as potting resin is provided around the device chip 1. A resin is applied, and the sealing resin 9 hermetically seals the cavity 8 formed between the printed wiring board 5 and the device chip 1. In this case, the sealing resin 9 flowing from the periphery of the device chip 1 into the inside of the functional surface 1a reaches the gap formed between the mounting surface of the printed wiring board 5 and the photoresist film 10 due to surface tension, The cavity 8 that does not suppress the surface wave of the functional surface 1a of the device chip 1 because it is reliably blocked at the position of the photoresist film 10
Can be formed.

Therefore, according to the structure of the first embodiment,
In this structure, since the recess 7 unlike the conventional case is not formed on the mounting surface of the printed wiring board 5, there is no need to design a special printed wiring board 5 for a specific surface acoustic wave device, and a commercially available The printed wiring board 5 has an inexpensive mounting structure that can easily cope with the design change of the surface acoustic wave device. Also, the photoresist film 10 to be used
Can be formed all at once during the manufacturing process of the surface acoustic wave device, so that the structure has a precise structure and is highly effective for mass production, and a reduction in product cost can be expected.

Although the liquid resin is used in the description of the first embodiment, a so-called B-stage solid encapsulating material can be used as the encapsulating resin 9 of the present invention. Needless to say again.

FIG. 3 is a sectional view of a second embodiment of the present invention, corresponding to FIG. 2. In the figure, the same structural parts as those in FIG. 2 are designated by the same reference numerals. The feature of the second embodiment is that
Double-frame-shaped deformed first photoresist film 10A
And the second photoresist coating 10B, and these photoresist coatings 10A and 10B prevent the sealing resin 9 from flowing into the cavity 8. That is, according to the first photoresist film 10A and the second photoresist film 10B, the inflow of the sealing resin 9 can be prevented more reliably than that of the structure of the first embodiment, and therefore the characteristics of the surface acoustic wave device. It is possible to obtain a mounting structure that fully exerts the above.

FIG. 4 shows a third embodiment of the present invention, which is a functional surface 2 of a device chip 21 made of, for example, ceramic.
1a has a pair of comb-shaped electrodes 12, 13, 14, 1
5, 16 and 17 form the surface wave propagation path 24, and the end bonding pads 12a, 13a, 14a and 15 of the comb-shaped electrodes 12, 13, 14, 15, 16 and 17 are formed.
Mounting bumps 20 having a height h1 (shown in FIG. 2) are arranged on a, 16a, 17a by a known forming method for connection with a circuit board such as a printed wiring board 5. And
As understood from FIG. 4, the bonding pads 12b and 17b are added to the central portion of the surface acoustic wave device, and the additional mounting bump 20B is also arranged on the surfaces of the bonding pads 12b and 17b.

The functional surface 2 of the device chip 21
A continuous rectangular frame-shaped photoresist coating 22 having a height h2 surrounding the surface wave propagation path 24 is formed on the la 1a by the same method as in the first embodiment. As shown in FIG. 2, the height h2 of the photoresist coating 22 is set so that the mounting bumps 20 of the surface acoustic wave device are connected to the conductive layer 5a of the printed wiring board 5 which is a circuit board. For the purpose of forming a slight gap with the surface of the mounting bump 20, the height is selected to be equal to or smaller than the height h1 of the mounting bump 20. In this case as well, the photoresist coating 22 is for the purpose of blocking the inflow of the sealing resin 9 to form cavities between the functional surface 21a of the device chip 21 and the mounting surface of the printed wiring board 5, and therefore is always continuous. It is not necessary to form the frame-shaped photoresist film, but for example, a dot-shaped or linear photoresist film arranged along the frame-shaped virtual pitch line may be used.

Also in the mounting process of this embodiment, a face-down bonding method is used in which the functional surface 21a of the device chip 21 faces the mounting surface of the printed wiring board 5 on which the conductive layer 5a is formed. In this case, device chip 2
1. Sealing resin 9 flowing from the periphery of 1 into the inside of the functional surface 21a
Reaches the gap formed between the mounting surface of the printed wiring board 5 and the photoresist coating film 22 due to surface tension, but is reliably blocked at the position of the photoresist coating film 22, and thus the functional surface of the device chip 21. The cavity 8 that does not suppress the surface wave of 1a can be formed.

Therefore, according to the structure of the third embodiment,
It has the same advantages as those of the first embodiment described above, but additionally has the advantage of increasing the degree of freedom in designing the surface acoustic wave and the device itself because the additional mounting bump can be arranged in the central portion of the surface acoustic wave device. .

[0018]

As is apparent from the above description, according to the present invention, it is not necessary to form a special recess or the like on the circuit board, so that the surface acoustic wave device can be freely mounted on the commercially available circuit board. As a result, the photoresist coating formed on the surface acoustic wave device can be collectively formed in the manufacturing process of the surface acoustic wave device, resulting in a mass-produced and inexpensive structure.

[Brief description of drawings]

FIG. 1 is an overall perspective view of a surface acoustic wave device used in the present invention.

FIG. 2 is an enlarged cross-sectional view of a surface acoustic wave device mounting structure according to a first embodiment of the present invention.

FIG. 3 is an enlarged sectional view of a surface acoustic wave device mounting structure according to a second embodiment of the present invention.

FIG. 4 is an overall perspective view of a surface acoustic wave device according to a third embodiment of the present invention.

FIG. 5 is an overall perspective view of a conventional surface acoustic wave device.

FIG. 6 is a cross-sectional view of a conventional surface acoustic wave device mounting structure.

[Explanation of symbols]

1,21 Device chip 1a, 21a Functional surface 2,3,12,13,14,15,16,17 Comb-shaped electrode 4,24 Surface wave propagation path 5 Printed wiring board 5a Conductive layer 6,6B, 20,20B Mounting bump 8 Cavity 9 Sealing resin 10, 10A, 10B, 22 Photoresist film

Claims (3)

[Claims] 1. A functional surface of a device chip forming a surface wave propagation path is made to face a mounting surface of a circuit board to be mounted,
In a mounting structure of a surface acoustic wave device in which a vibrating space is maintained between the functional surface and the mounting surface, the periphery of a device chip is covered with a sealing resin, and the surface wave propagation path is surrounded and the surface wave is surrounded. A photoresist film lower than the mounting bumps of the propagation path is formed on the functional surface, and with the mounting bumps connected to the conductive layer of the circuit board, there is a slight gap between the surface of the photoresist film and the mounting surface. Is formed, and the sealing resin is terminated at the position of the photoresist coating, the mounting structure of the surface acoustic wave device. 2. The surface acoustic wave device mounting structure according to claim 1, wherein the photoresist coating is formed in a continuous frame shape surrounding the surface wave propagation path. 3. The mounting structure for a surface acoustic wave device according to claim 1, wherein the photoresist coating is a discontinuous point or linear resist film surrounding the surface wave propagation path.