JPH04343511A - surface acoustic wave device - Google Patents

Abstract

PURPOSE:To obtain an element having a soldering enabled conductive metallic pad having shock resistance by using a conductive metallic pad consisting of two layer films, i.e., a prescribed metal as a ground and a required conductive metal as an upper layer. CONSTITUTION:A surface acoustic wave element pattern 6 and a solering enable conductive metallic pad 4 are formed on a piezoelectric base chip 3 so as to be superposed to each other. Since a double-film conductive metallic pad using Cr as a ground and a conductive metal such as Au and Ag as an upper layer is used as the pad 4 and adhesion to the chip 3 is improved, the surface acoustic wave element having the soldering enabled metallic pad with improved shock resistance and improving its aging effect can be obtained.

Description

[Detailed description of the invention]

0001

[Industrial Application Field] The present invention is applicable to mobile communication devices, TVs,
The present invention relates to surface acoustic wave elements used in VTRs and the like.

0002

2. Description of the Related Art In conventional techniques, solderable conductive metal pads are not formed, but pads are formed from the same material as the surface acoustic wave element as part of the pattern of the surface acoustic wave element. That is, the external terminal connection portion of the surface acoustic wave element and the surface acoustic wave element have the same pattern. Therefore, to connect the surface acoustic wave element pattern and the lead wires, you can use conductive paste and glue them together, or you can glue a small piece of a piezoelectric substrate on which the surface acoustic wave element pattern is formed to the stem. The element pattern and lead wires were connected by wire bonding.

0003

[Problems to be Solved by the Invention] In the above-mentioned prior art, a conductive paste must be used for connection with the lead wire, and the aging characteristics of the surface acoustic wave element are affected by the gas generated from the conductive paste. The problem was that the condition deteriorated. In addition, since wire bonding was generally used to connect the lead wires, space for routing the wires had to be taken into consideration, which resulted in the problem that the case in which the surface acoustic wave element was housed would become large. had.

An object of the present invention is to provide a conductive metal pad that can be soldered to a lead wire without using conductive paste or wire bonding, and to manufacture a solderable conductive metal pad that has excellent impact resistance. It provides technology.

[0005]

[Means for Solving the Problems] The above object is to provide a surface acoustic wave element and a solderable conductive metal pad on a small piece of a piezoelectric substrate so that they intersect, and connect external terminals such as lead wires with the solder. This is achieved by connecting by attaching. Furthermore, by making the conductive metal pad a two-layer film of gold or the like with chromium as the lower layer, a solderable conductive metal pad with excellent impact resistance can be obtained.

[0006]

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is a plan view showing the appearance of a surface acoustic wave device of the present invention. For reference, it is written so that the inside of shell 1 can be seen through it.

A pattern 6 of surface acoustic wave elements and conductive metal pads are formed on the small piece 3 of the piezoelectric substrate. In this embodiment, surface acoustic wave elements 6 made of aluminum are provided on conductive metal pads 4 so as to cross each other. That is, this is an example in which the surface acoustic wave element pattern 6 is formed after the conductive metal pad 4 is formed. A lead wire that passes through the conductive metal pad 6 and the stem 2 and is fixed with a hermetic seal or the like is fixed to the conductive metal pad 4 by soldering. After this fixing is completed, the shell 1 is fixed to the stem 2 by resistance welding or the like to form one package. Here, the pattern of the surface acoustic wave element is an example of a one-port surface acoustic wave resonator, but any pattern that applies surface acoustic waves may be used, such as a filter or a delay element.

FIGS. 2 and 3 are a front view and a sectional view showing a conventional surface acoustic wave element. A small piece 3 of the piezoelectric substrate is bonded to the stem 2 with resin or the like. Most of the patterns of surface acoustic wave elements are formed of aluminum metal. Therefore, since aluminum metal cannot be soldered, in the conventional technique, it was connected to the lead wire 5 using a conductive wire 7 made of aluminum, gold, or the like, as shown in the figure. Therefore, the process for fixing the small piece 2 of the piezoelectric substrate and also the conductive wire 7
In the conventional technology, two steps are required to connect the lead wire to the lead wire using the stem 2. However, in the present invention, the lead wire 7 and the small piece 3 of the piezoelectric substrate can be strongly connected by soldering. It also has the advantage that the small pieces of the piezoelectric substrate do not need to be glued together unless necessary.

FIG. 4 is a diagram showing the rate of change in frequency over time when using the surface acoustic wave element according to the present invention and the conventional technique. Here we show the frequency change of a surface acoustic wave resonator using a quartz substrate. In the surface acoustic wave element of the present invention, that is, one in which a conductive metal pad is formed and connected to a lead wire by soldering, the frequency changes slightly downward after measurement starts, but the frequency does not change even after time passes. becomes constant. On the other hand, a surface acoustic wave resonator using the conventional technology, that is, a small piece 3 of a piezoelectric substrate on which a pattern 6 of a surface acoustic wave element is formed as shown in FIGS. 2 and 3 is fixed to the stem 2 with adhesive, and then In the case where the conductive wire 7 is connected to the lead wire 5 by a wire bonding machine, the frequency changes greatly over time after the measurement is started. This is because an adhesive is used to fix the small piece 3 of the piezoelectric substrate and the stem 2. When an adhesive is used, gas from the adhesive is deposited on the surface acoustic wave element, causing a frequency change. Alternatively, even if a conductive paste is used to connect to the lead wire without soldering, gas is released from the conductive paste in the same way as with adhesive, causing a frequency change.

Next, the manufacturing method of the present invention will be explained using FIGS. 5 and 6. FIG. 5 shows the steps up to forming a solderable conductive metal pad, and FIG. 6 shows the steps up to forming a surface acoustic wave element pattern thereon. The reason why the surface acoustic wave element pattern is provided after the solderable conductive metal pads are provided is as follows. A method such as wet etching is used when forming the conductive metal pad. For example, a mixed solution of nitric acid and hydrochloric acid is used for wet etching of gold. If a mixed solution of nitric acid and hydrochloric acid is used to form this conductive metal pad after installing a surface acoustic wave element, the surface acoustic wave element, which is generally made of aluminum metal, will dissolve in this solution. There are cases. Therefore, in order to eliminate such risks and improve yield, it is advantageous to form conductive metal pads before forming surface acoustic wave elements.

In FIG. 5A, a gold film is deposited on the cleaned piezoelectric substrate 8 by sputtering. The sputtering method can deposit a metal film on a substrate with good adhesion. Therefore, in this embodiment, as shown in FIG.
In particular, in cases where the conductive metal pad is not fixed, it is necessary that the adhesion of the conductive metal pad be strong, so a method using a sputtering method is preferable. If it is desired to further increase the adhesion, a chromium or titanium film should be applied as a lower layer between the piezoelectric substrate piece 8 and the gold film 9. Generally, the thickness of the chromium metal film is about 100 angstroms, and the thickness of the gold film is about 900 to 1000 angstroms. The same holds true when silver is used as the pad.

Next, a resist resin is applied as shown in FIG. 1(b). In this embodiment, a positive resist resin is used in which the portion exposed to light dissolves in a developing solution. Next, Figure 1(c)
), exposure is performed using a photomask 11 as shown in FIG.
Develop as in d).

In FIG. 1(e), gold is etched. The mixed solution of nitric acid and hydrochloric acid mentioned earlier is used for etching gold, but dry etching using plasma may also be used. After the etching is completed, remove unnecessary resist resin as shown in Figure 1(f).
The remaining gold film becomes a solderable conductive metal pad.

FIG. 6 is a diagram showing how a pattern of a surface acoustic wave element is formed using the lift-off method. Of course, it is not necessary to use the lift-off method, and wet etching or dry etching may be used as in the case of conductive metal pads.

When forming a pattern by the lift-off method, the resist resin shown in FIG. 2(a) needs to be about 2 to 3 times as thick as the metal film forming the surface acoustic wave element.
However, conversely, even if there is a step such as a gold film 9 that serves as a conductive metal pad on the substrate, the resist resin 10 must be applied thickly, so the step can be avoided. This has the advantage that the influence of the resist resin 10 can be eliminated to some extent and the resist resin 10 can be applied uniformly. It is important to uniformly apply the resist resin 10 in order to uniformly perform the exposure shown in FIG. 2(b).

Subsequently, exposure and development are performed as shown in FIGS. 2(b) and 2(c). Thereafter, as shown in FIG. 2(d), aluminum is vapor-deposited and the unnecessary resist resin 10 is peeled off, thereby forming a surface acoustic wave element pattern as shown in FIG. 2(e).

After forming the surface acoustic wave element as shown in FIGS. 5 and 6, the lead wires 5 are soldered to the pad portions as shown in FIG. 7(a).

[0018]

According to the present invention, external connection electrodes of a surface acoustic wave element on a small piece of a piezoelectric substrate are provided so as to overlap with solderable conductive metal pads, so that external terminals such as lead wires can be Connection can be made by soldering. This has the effect of improving the aging characteristics of the surface acoustic wave element. In addition, by making the conductive metal pad a two-layer film with a chromium base layer and a conductive metal such as gold or silver as an upper layer, the adhesion between the piezoelectric substrate and the solderable conductive pad is improved and impact resistance is improved. It also has the effect of making it difficult to peel off even when

[Brief explanation of drawings]

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

FIG. 2 is a front view showing the appearance of a surface acoustic wave device according to the prior art.

FIG. 3 is a cross-sectional view showing the appearance of a surface acoustic wave device according to the prior art.

FIG. 4 is a characteristic diagram showing the rate of change in frequency over time when the surface acoustic wave element according to the present invention and the conventional technology are used.

FIG. 5 is a cross-sectional view showing the steps up to forming a solderable conductive metal pad.

FIG. 6 is a cross-sectional view showing the steps from forming a solderable conductive metal pad to forming a surface acoustic wave element.

[Explanation of symbols]

1 Shell 2 Stem 3. Small piece of piezoelectric substrate 4 Conductive metal pad 5 Lead wire 6　　　　Surface acoustic wave element pattern 7 Conductive wire 8 Piezoelectric substrate 9 Gold film 10 Resist resin 11 Photomask 12 Aluminum film

Claims (3)

[Claims] 1. A surface acoustic wave element pattern on a small piece of a piezoelectric substrate is provided so as to overlap a solderable conductive metal pad, and the pad is connected to an external terminal such as a lead wire by soldering. A surface acoustic wave element characterized by being connected to. 2. After forming a solderable conductive metal pad on a piezoelectric substrate forming a surface acoustic wave element,
The surface acoustic wave device according to claim 1, wherein a pattern of the surface acoustic wave device is formed. 3. The conductive metal pad according to claim 1, wherein the conductive metal pad is a two-layer film having a lower layer of chromium or titanium and an upper layer of a solderable conductive metal such as gold, silver, or nickel. Surface acoustic wave device.