JPS58129818A - Surface acoustic wave device - Google Patents

Abstract

PURPOSE:To simplify the process of manufacturing a surface acoustic wave device by forming interdigital electrodes and electrode terminal parts of nickel or alloy consisting principally of nickel. CONSTITUTION:On one surface of a surface wave substrate 1 made of a polarized piezoelectric ceramic plate, etc., nickel or nickel alloy is varpo-deposited and etched to form a surface wave electrode. The surface wave electrode consists of input and output interdigital electrodes 2 and 3 and electrode terminal parts 4 and 5, and 6 and 7 led out of those electrodes; surface wave absorbers 8 and 9 are provided on unneccessary wave propagation paths outside of the electrodes 2 and 3, and external terminals 10, 11, 12, and 13 are soldered directly to the electrode terminal parts 4, 5, 6, and 7. The electrode made of nickel or nickel alloy has superior resistance to a solvent, so it is unneccessary to form a protective film on the electrode during the soldering.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a surface acoustic wave device, and more particularly to a surface acoustic wave device in which external terminals are soldered and coated with a resin outer layer.

In general, a surface acoustic wave device is made up of an interdigital electrode formed on a surface wave substrate, in which a large number of electrode fingers with a fine electrode width are arranged. A metal material with low resistance and light specific gravity is selected, and a vapor-deposited film of aluminum is commonly used, and a 7-domain wire is wire-bonded to the electrode terminal portion made of the same aluminum film. Using a metal material with low resistivity as an electrode material is because the electrode film is thin and elongated, which causes insertion loss due to the resistance of the electrode film, and manufacturing variations during electrode formation (variations in electrode thickness, width, and length). This is because, although variations occur in the insertion loss due to this, the variation in the insertion loss can be suppressed by using a metal material with a low specific resistance. In addition, the center frequency changes depending on the mass of the electrode, but when forming the electrode, the thickness of the electrode
When the width and area vary, the degree of change in the center frequency also varies, and in order to reduce this variation, a metal material with a light specific gravity is used as the electrode material.

Furthermore, the reasons why aluminum electrodes are commonly used are that aluminum is available at low cost, has strong vapor deposition strength, is easy to bond, and can be used even with fine and complex electrode patterns such as interdigital electrodes. It may also be easier to perform etching treatment.

On the other hand, surface acoustic wave devices packaged with an outer resin layer have multiple electrode terminals on a surface wave board arranged on one side of the board, and external terminals are directly soldered to these electrode terminals to create a single package. , is constructed in a line shape, and the entire substrate is coated with an outer layer resin, leaving a gap in the surface wave propagation area.

Even in surface acoustic wave devices having such a structure, a vapor-deposited aluminum film is used for the reasons mentioned above.

However, when a terminal is directly soldered to an aluminum vapor-deposited film (electrode terminal portion), a+f' aluminum solder must be used, resulting in poor work efficiency. Therefore, another electrode, such as a nickel, copper, or silver electrode, is usually formed on the aluminum electrode terminal as a soldering electrode. Further, since the aluminum vapor-deposited film has poor water resistance and solvent resistance, a protective film is formed on the electrode of the aluminum vapor-deposited film. A surface acoustic wave device having such a structure has the disadvantage that a separate electrode for soldering must be provided, and in some cases a protective film must be provided on the electrode, resulting in an increase in the number of steps.

Therefore, the present invention maintains almost the same characteristics as when using an electrode made of an aluminum vapor-deposited film as described above, and
An object of the present invention is to provide a surface acoustic wave device that can reduce the number of manufacturing steps.

Embodiments of the present invention will be described in detail below with reference to the drawings.

In Fig. 1, reference numeral 1 denotes a surface wave substrate made of a single piezoelectric ceramic plate that has been subjected to polarization treatment, and a metal material made of nickel or nickel alloy is deposited and etched on one side of this substrate 1. A surface wave electrode is formed. As a nickel alloy, for example, 70% nickel
Ni-Al alloy consisting of S and 30% by weight of aluminum,
Ni-Cu consisting of 70% by weight of nickel and 30% by weight of copper
Used in alloying furnaces. This surface wave electrode consists of an output interdigital electrode 2.3 and an electrode terminal portion 4.5.6.7 led out from these electrodes. A surface wave absorber 8.9 is provided on the unnecessary wave propagation path located outside the interdigital electrode 2.3, and the external terminals 10.11.
12.13 are directly soldered to the electrode terminal portions 4.5.6.7, respectively.

Since nickel and nickel alloy electrodes have excellent solvent resistance, there is no need to form a protective film on the interdigital electrodes when soldering. Then, the entire substrate is dipped in resin with a void-forming material such as wax applied on a predetermined surface wave propagation path to form a resin outer layer 14. When the resin hardens, the wax melts and creates voids on the predetermined propagation path. It is formed.

According to this embodiment, there is no need to provide soldering electrodes or protective films, and the number of steps and manufacturing days can be significantly reduced. Therefore, even if nickel or nickel alloy is more expensive than aluminum, it can be manufactured at a lower cost overall. Furthermore, changes in insertion loss and center frequency due to resistance, as well as their variations, were tested under the same conditions except for the electrode material and related parts, and the results were as shown in Table 1. In other words, the insertion loss when using a nickel or nickel alloy electrode is very different from that when using an aluminum electrode (and the variation is not a practical problem compared to using an aluminum electrode and a π type). In addition, the change in center frequency when using nickel or nickel alloy electrodes is several tens of kHz lower than when using aluminum electrodes, but the variation is almost the same as when using aluminum electrodes. Even if the frequency drop is due to the electrode material, there is no problem if the frequency drop is taken into consideration in advance when designing the electrode pattern.

Table 1 We also conducted a special moisture resistance test (pressure Kutzker test) in water vapor at 120°C and 2 atm pressure for each electrode material.
As a result of performing this test on 0 samples, the number of defective products whose frequency characteristics changed was as shown in Table 2. In other words, the special test results were better when using nickel or nickel alloy electrodes than when using aluminum ram electrodes.

Table 2 Furthermore, when using nickel or nickel alloy electrodes as in this example, removal of void-forming materials such as wax during curing of the outer layer resin is easier than when using conventional aluminum electrodes. At the same time, it is possible to achieve the effects that the process can be performed more reliably and the predetermined frequency characteristics can be achieved more reliably. This is thought to be because, while in the conventional example, the gap forming material is provided on the protective film on the aluminum electrode, in this example it is provided directly on the electrode.

As explained above, the present invention uses nickel or a nickel alloy to form the interdigital electrode and the electrode terminal portion, so it maintains almost the same characteristics as conventional aluminum electrodes while reducing the manufacturing process. This has the effect of reducing the number of manufacturing days required.

[Brief explanation of drawings]

FIG. 1 is a diagram showing an embodiment of a surface acoustic wave device according to the present invention. DESCRIPTION OF SYMBOLS 1... Surface wave board, 2.3... Interdigital electrode, 4.5.6.7... Electrode terminal part, 10.11.
12.13...External terminal. Patent applicant Murata Manufacturing Co., Ltd.

Claims (1)

[Claims] A surface acoustic wave device characterized in that an interdigital electrode and an electrode terminal portion derived from the electrode are formed of nickel or a nickel alloy containing nickel as a main component.