JPS62141811A - Surface acoustic wave element - Google Patents

Abstract

PURPOSE:To eliminate a considerable change of the variation of a center frequency to temperature and the insertion loss by fixing a surface acoustic wave element chip into a case with an adhesive wheer hard particles selected from groups consisting of metallic materials and inorganic materials are mixed. CONSTITUTION:A piezoelectric substrate 2 is fixed onto a metallic base 1 by adhesion with a silicone adhesive 7 where alumina hard particles 8 having 25-30mu diameter are mixed. Hard particles 8 mixed in the silicone adhesive 7 function as a post for the vertical pressuring force applied at the wire bonding time, and the silicone adhesive functions an absorber for the change of stress due to expansion and contraction in the lengthwise direction at the thermosetting time or the environment change time, thereby preventing the variance of the center frequency and the insertion loss.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a surface acoustic wave device used as an oscillation and resonance device as a filter or as a frequency source in a high frequency band, from several thousand MHz to several GHz.

2. Description of the Related Art Conventional surface acoustic wave elements are shown in FIGS. 2) to 2(C). This surface acoustic wave element is manufactured as follows.

First, interdigital electrodes 3 made of an At thin film are placed on a piezoelectric substrate 2 made of quartz, lithium tantalate, lithium niobate, etc.
It is formed by photolithography technology, and then cut into two parts with predetermined dimensions.

Next, the piezoelectric substrate 2 is fixed onto the metal base 1 via an epoxy adhesive 9.

Next, with a bonding wire 5 of At or Au.

Connecting electrode 4 and lead electrode 6 are connected. Thereafter, a metal cap (not shown) is heat-sealed to complete the product.

In addition, the piezoelectric substrate, the plate 2, the interdigital electrode 3, and the connection electrode 4
constitutes a surface acoustic wave device chip.

Further, the metal base 1 and the metal cap constitute a case for housing two surface acoustic wave elements.

That is, because a surface acoustic wave element cannot have a protective film attached to its electrode surface due to its nature, it is necessary to accommodate it in a package cage in some way. Therefore, it is fixed to an ordinary ceramic or metal base using an epoxy or silicone adhesive.

[Problem that the invention seeks to solve]

However, in the above-mentioned method of fixing surface acoustic wave device chips using only epoxy-based or silicone-based adhesives, 2. For example, epoxy-based adhesives are thermosetting, so 1. They have no elasticity and do not exhibit piezoelectric properties after being adhesively fixed. Stress is generated on the substrate and has a major impact on the electrical characteristics.

It has the disadvantage of causing a significant change in the center frequency and an increase in loss. In addition, when bonding and fixing with a flexible type silicone adhesive, although there is less stress due to heat curing, the ultrasonic energy applied during wire binding to connect each electrode after bonding and fixing becomes uneven, resulting in poor connection conditions. There is a problem in that variations occur and the reliability of the connection is impaired.

SUMMARY OF THE INVENTION Therefore, an object of the present invention is to provide a surface acoustic wave device that eliminates such drawbacks.

[Means to Solve the Problem] According to the present invention, in a surface acoustic wave device including one surface acoustic wave device chip housed in a case, a material selected from the group consisting of metal and inorganic material is used. A surface acoustic wave device is obtained, characterized in that the surface acoustic wave device chip is fixed in the case with an adhesive mixed with hard particles.

〔Example〕

Next, the present invention will be explained in detail with reference to the drawings. FIGS. 1A to 1C show an embodiment of the present invention.

Using an At thin film on a piezoelectric substrate 2 made of quartz, lithium tantalate, lithium niobate, etc., interdigital electrodes 3 are formed by photolithography, and then cut and divided into predetermined dimensions.

Next, the piezoelectric substrate 2 is adhesively fixed onto the metal paste 1 via a silicone adhesive 7 having a diameter of 25 to 30 μ and mixed with hard particles 8 made of alumina. After several hours of drying time,
The connection electrode 4 and the lead electrode 6 are connected with a bonding wire 5 made of At or Au. At this time, silicone adhesive 7
The hard particles 8 mixed therein play the role of supports against the vertical pressing force applied during wire binding, and on the other hand, expand in the longitudinal direction during heat curing or due to environmental changes.

With respect to changes in stress due to shrinkage, the silicone adhesive acts as an absorbent, thereby preventing fluctuations in the center frequency and increases in insertion loss.

Note that the diameter of the hard particles is preferably selected depending on the dimensions of the element, etc.

Furthermore, the adhesive is not limited to silicone-based adhesives, but may be one that has a low degree of thermosetting.

〔Effect of the invention〕

As explained above, according to the present invention, it is possible to stabilize the center frequency by eliminating the insertion loss and the large change in the fluctuation width of the center frequency with respect to the temperature, which is an especially important element in the electrical characteristics of the two-surface acoustic wave element. It is possible to plan.

[Brief explanation of drawings]

FIG. 1(A) is a perspective view showing one embodiment of the surface acoustic wave device according to the present invention, and FIG. 1) and FIG. 1(C) are sectional views of the surface acoustic wave device during the manufacturing process. or. FIG. 2(A) is a perspective view showing a conventional surface acoustic wave element. FIGS. 2(B) and 2(C) are cross-sectional views during the manufacturing process of a conventional surface acoustic wave device. DESCRIPTION OF SYMBOLS 1... Metal base, 2... Piezoelectric substrate, 3... Cross-finger electrode, 4... Connection electrode, 5... Bonding wire, 6... Lead electrode, 7... Silicone adhesive. 8...Hard spot particles, 9...Epoxy adhesive.

Claims (1)

[Claims] 1. In a surface acoustic wave device in which a surface acoustic wave device chip is housed in a case, an adhesive mixed with hard particles selected from the group consisting of metals and inorganics can be used to
A surface acoustic wave device, characterized in that the surface acoustic wave device chip is fixed within the case.