JPH0590881A - Circuit board for mounting surface acoustic wave device - Google Patents

Abstract

PURPOSE:To enable a circuit board for mounting a surface acoustic wave device to obtain a large electromagnetic shield effect, to protect the surface acoustic wave device from electromagnetic interference, and to enhance the reliability of the board by mounting the ground electrode at a position opposite to a tandem type electrode (IDT) prepared on the functional surface of the device. CONSTITUTION:A surface acoustic wave device A is mounted at a predetermined position on a circuit board 5 such that the attitude of a functional surface 3a where IDT 2 is prepared is opposite to the circuit board 5. By loading the circuit board 5 where wiring 11 and ground electrode 12 are mounted at predetermined position with a device A and by connecting the input/output electrode 2a of the device A to the wiring 11 for the board 5 using a connecting member such as solder, the device A is mounted. Accordingly, via gap (oscillation space) 7, the ground electrode 12 is prepared in a section opposite to the IDT 2 mounted onto the functional surface 3a of the device A, whereby electromagnetic shield (grounding electrode 12) can be applied to a section close to IDT 2, and whereby an electromagnetic shield effect can be obtained that is usually greater than the shield effect which can be obtained when the grounding electrode is mounted on the surface 3b at the side opposite to the functional surface 3a having a thickness of 0.5-0.8mm in a surface acoustic wave device 3.

Description

Detailed Description of the Invention

[0001]

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

[0002]

2. Description of the Related Art For example, as shown in FIG. 5, a surface acoustic wave element 23 used in a conventional surface acoustic wave device is
It is formed by disposing a comb-teeth electrode (IDT) 22 at a predetermined position on one main surface of a surface acoustic wave substrate (piezoelectric substrate) 21. Input / output electrodes 22a connected to the IDT 22 are arranged on both ends of the surface acoustic wave substrate 21. Then, the IDT 2 of the surface acoustic wave element 23
When a voltage is applied to 2, the piezoelectric effect causes distortion in the vicinity of the surface of the surface acoustic wave substrate 21, and this distortion becomes a surface wave and propagates on the surface.

That is, the functional surface (vibration surface) 23a of the surface acoustic wave element 23 constituting the surface acoustic wave device, on which the IDT 22 is disposed, is a vibration surface for generating surface waves and a surface generated by the IDT 22. It also functions as the surface wave propagation path 24 for propagating waves. Therefore, in order for the surface acoustic wave element 23 to function normally, the principal surface (functional surface) 23a of the surface acoustic wave element 23, on which the IDT 22 is disposed, is prevented from coming into contact with other members or the like. There is a need.

Therefore, conventionally, the surface acoustic wave element is housed in a hermetic case or is resin-molded to improve reliability. However, with this method, there is a problem that the manufacturing cost increases and the size cannot be coped with downsizing, so that the surface acoustic wave element is directly mounted on the circuit board without being housed in the case. A mounting type surface acoustic wave device has been attracting attention.

However, even in the bare chip mounting type surface acoustic wave device, if the surface of the surface acoustic wave device is mounted with its functional surface facing upward, it is necessary to perform wire bonding or prevent characteristic deterioration due to adhesion of foreign matter. For this purpose, it is necessary to cap the surface wave propagation path, which complicates the mounting work and hinders high-density mounting.

Therefore, as shown in FIG. 6, a surface to be mounted on the circuit board 25 with the functional surface 23a of the surface acoustic wave element 23 facing the circuit board 25 and a joining member 26 such as a conductive paste or solder interposed therebetween. Down-bonding type surface acoustic wave devices have been developed and used.

[0007]

However, the surface acoustic wave device mounted by the face-down bonding described above is not particularly capped, is exposed, and is not electromagnetically shielded. However, there is a problem that it is susceptible to electromagnetic interference and its reliability is low.

The present invention solves the above-mentioned problems, and the surface acoustic wave device to be mounted is subjected to electromagnetic interference without complicating or increasing the size of the structure of the surface acoustic wave device. An object of the present invention is to provide a circuit board for mounting a surface acoustic wave device which can be prevented.

[0009]

In order to achieve the above object, a circuit board for mounting a surface acoustic wave device according to the present invention has electrodes such as comb-shaped electrodes provided on one main surface of the surface acoustic wave board. The surface acoustic wave device is connected by a joining member in a state where the functional surfaces on which the comb-teeth-shaped electrodes are disposed face each other and the functional surfaces are separated by a distance that forms a predetermined vibration space. The circuit board to be fixed is characterized in that a ground electrode is arranged at a portion facing a comb tooth-shaped electrode arranged on the functional surface of the surface acoustic wave device.

[0010]

In the circuit board for mounting the surface acoustic wave device of the present invention, the circuit board is provided at a portion of the circuit board facing the comb-teeth-shaped electrode provided on the functional surface of the surface acoustic wave device (surface acoustic wave element). Since the ground electrode (ground pattern) mounted is very close to the comb-shaped electrode of the surface acoustic wave device, it becomes possible to reliably protect the mounted surface acoustic wave device from electromagnetic interference. The electromagnetic shield function is greater than, for example, the case where the surface opposite to the functional surface of the surface acoustic wave device (surface acoustic wave element) is provided with the ground electrode. Furthermore, in the case of a circuit board having hot lines formed on the back surface of the circuit board, the ground electrode functions as an electromagnetic shield effective against electromagnetic interference from the back surface.

[0011]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a plan view showing a surface acoustic wave device mounting circuit board according to an embodiment of the present invention, and FIG. 2 is a sectional view thereof.

The surface acoustic wave device A (surface acoustic wave element 3) used in this embodiment has a predetermined surface acoustic wave substrate 1 as shown in FIG. 5 used for explaining a conventional example. It is formed by disposing a comb-shaped electrode (IDT) 2 and an input / output electrode 2a at a position.

As shown in FIGS. 1 and 2, the circuit board 5 on which the surface acoustic wave device A is mounted is located at a position facing the input / output electrodes 2a formed on the functional surface 3a of the surface acoustic wave device A. In addition to the wiring (input / output terminal) 11, a ground electrode (ground pattern) 12 is formed at a position facing the IDT 2 on the functional surface 3a and around the position.

The surface acoustic wave device A is mounted at a predetermined position on the circuit board 5 in such a posture that the functional surface 3a on which the IDT 2 is formed faces the circuit board 5. That is, the surface acoustic wave device A is placed on the circuit board 5 on which the wiring (input / output terminal) 11 and the ground electrode 12 are formed at predetermined positions, and the surface acoustic wave device A is connected by the joining member 6 such as solder. The surface acoustic wave device A is mounted by connecting the output electrode 2 a to the wiring 11 of the circuit board 5.

A gap (vibration space) 7 is formed between the circuit board 5 and the functional surface 3a of the surface acoustic wave device A mounted on the circuit board 5 in this manner, but the thickness thereof is about The thickness is 0.2 to 0.3 mm, which is smaller than the thickness of the surface acoustic wave element 3 (surface acoustic wave substrate 1) which is usually about 0.5 to 0.8 mm.

Therefore, the IDT formed on the functional surface 3a of the surface acoustic wave device A through the gap (vibration space) 7.
By forming the ground electrode 12 at a portion facing the IDT 2, it becomes possible to provide an electromagnetic shield (ground electrode 12) at a position close to the IDT 2, and, for example, normally, the.
It is possible to obtain an electromagnetic shield effect larger than that in the case where the ground electrode (electromagnetic shield) is formed on the surface 3b (FIG. 2) opposite to the functional surface 3a of the surface acoustic wave element 3 having a thickness of 5 to 0.8 mm.

In recent years, a circuit board having wiring on both sides thereof has been widely used. According to the present invention, electromagnetic interference from a hot line arranged on the back surface of the circuit board is effective. It is possible to prevent noise and suppress noise.

In the above embodiment, the case where the ground electrode 12 is integrally formed has been described. However, as shown in FIG. 3, the ground electrode 12 is electrically disconnected to reduce the direct wave and to improve the characteristics. In some cases it can be improved.

Further, as shown in FIG.
May be connected to the ground side (ground terminal) 11a of the wiring (input / output terminal) 11 on the circuit board.

In the surface acoustic wave device mounting circuit board of the present invention, by forming the ground electrode 12 even around the portion of the surface acoustic wave device A facing the IDT, a greater electromagnetic shield effect can be obtained. can get. Further, even if a small gap is formed in the ground electrode 12 in order to electrically separate the ground electrode 12, the electromagnetic shield effect is not significantly reduced by that.

Further, in the present invention, there are no particular restrictions on the materials constituting the circuit board and the ground electrode,
The circuit board and the ground electrode can be formed by using ordinary circuit board materials and electrode materials.

[0022]

As described above, in the surface acoustic wave device mounting circuit board of the present invention, the ground electrode is formed at a position facing the comb-teeth-shaped electrode formed on the functional surface of the surface acoustic wave device. Since it is possible to provide a shield at a position extremely close to the comb-shaped electrode, for example, an electrode (electromagnetic wave) is provided on the surface opposite to the functional surface of the surface acoustic wave device (the surface acoustic wave element constituting the surface acoustic wave device). A large electromagnetic shield effect can be obtained as compared with the case where the shield is applied, and the surface acoustic wave device can be protected from electromagnetic interference and reliability can be improved.

Further, in the case of a circuit board in which hot lines are also formed on the back surface of the circuit board, effective electromagnetic shielding can be performed against electromagnetic interference from the back surface.

[Brief description of drawings]

FIG. 1 is a plan view showing a surface acoustic wave device mounting circuit board according to an embodiment of the present invention.

FIG. 2 is a cross-sectional view showing a state in which a surface acoustic wave device is mounted on a surface acoustic wave device mounting circuit board according to an embodiment of the present invention.

FIG. 3 is a plan view showing a surface acoustic wave device mounting circuit board according to another embodiment of the present invention.

FIG. 4 is a plan view showing a surface acoustic wave device mounting circuit board according to still another embodiment of the present invention.

FIG. 5 is a plan view showing a surface acoustic wave element used in the present invention and a conventional example.

FIG. 6 is a sectional view showing a face-down bonding type surface acoustic wave device to which the present invention is related.

[Explanation of symbols]

 A surface acoustic wave device 1 surface acoustic wave substrate 2 comb-shaped electrode (IDT) 2a input / output electrode 3 surface acoustic wave element 3a functional surface 5 circuit board 7 vibration space 12 earth electrode (earth pattern)

Claims (1)

[Claims] 1. A surface acoustic wave device in which an electrode such as a comb-shaped electrode is disposed on one main surface of a surface acoustic wave substrate, and the functional surfaces on which the comb-shaped electrode is disposed face each other. A circuit board that is connected and fixed by a joining member in a state in which the functional surface is separated by a distance for forming a predetermined vibration space, and a comb-shaped electrode disposed on the functional surface of the surface acoustic wave device. A circuit board for mounting a surface acoustic wave device, characterized in that a ground electrode is provided in a facing portion.