JPH11234082A - Surface acoustic wave device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve the strength and durability of an electrode of a surface acoustic wave device which is mounted on a substrate by the flip-chip bonding by providing a chromium layer and a nickel layer, formed on the surface of a chrome layer on the surface of an aluminum electrode pad and forming a gold electrode layer on the surface of the nickel layer. SOLUTION: An inter digital electrode and a pad (aluminum film) 11 that is used for connection to an external circuit are formed on the surface of a piezoelectric substrate 10 of crystal, etc., in the processes of evaporation, etching, etc. A chromium layer 12 is formed similarly on the surface of the pad 11 as a 1st barrier layer, and a nickel layer 13 is formed on the layer 12 as a 2nd barrier layer. Then a gold layer 14 is formed on the surface of both layers 12 and 13, which are stacked on each other as an oxidization preventing film of both layers 12 and 13. The thickness of the layer 14 is made small compared with other layers. Then by forming a gold bump is formed on the surface of the layer 14, the adhesion force between the bump and an electrode pad is reinforced.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to an electrode structure of a surface acoustic wave device, and more particularly to a surface acoustic wave device mounted on a substrate and packaged by face-down bonding.

[0002]

2. Description of the Related Art In the field of surface acoustic wave devices, demands for chip formation and miniaturization are increasing. Face down bonding on a substrate surface has been studied, and a method of forming bumps on electrode pads has been studied. Is being put to practical use. The interdigital electrode of the surface acoustic wave element is made of aluminum or an aluminum alloy, and is connected to a wiring conductor on the substrate by a gold bump or the like.

When a base aluminum electrode and a gold bump are brought into direct contact with each other, a dissimilar metal compound is formed, which causes a change in composition. As a result, quality such as mechanical adhesive strength is deteriorated and electrical characteristics are also likely to deteriorate. Therefore, it is general that the barrier layer is made of a transition metal or a multilayer of gold, platinum, palladium or the like, and bumps are formed on the surface thereof.
For example, Japanese Patent Application Laid-Open No. 8-307192 discloses a technique in which the above-described metal layer is formed on the surface of aluminum, and a gold bump is formed thereon.

[0004] However, in such a configuration, the hardness of the barrier film becomes high, and it becomes difficult to set conditions such as electric power and load at the time of bump formation. When the conditions are set to be strong, the film is likely to be damaged, and when the conditions are set to be weak, the phenomenon of a decrease in adhesive strength occurs. In the flip chip bonding in the next step, the barrier film easily penetrates in thermocompression bonding and thermocompression bonding using ultrasonic waves.

[0005]

SUMMARY OF THE INVENTION The present invention provides an electrode structure capable of maintaining sufficient mechanical strength during bump formation and bonding and maintaining stable quality without causing a change in composition. What you get.

[0006]

According to the present invention, a barrier layer having two layers is provided.
The above problem is solved by forming a layer.

That is, in a surface acoustic wave device having interdigital electrodes made of aluminum and electrode pads for connecting them to an external circuit, and being face-down bonded by bumps connected to the electrode pads, in the surface acoustic wave device, A chromium layer is provided on all or a part of the surface, and a nickel layer is formed on the surface of the chromium layer. The gold electrode layer is formed on the surface of the nickel layer.

[0008]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The electrodes of a surface acoustic wave device according to the present invention are composed of the following four layers. Aluminum underlayer Chromium barrier layer Nickel barrier layer Gold surface layer

Further, by extending the bump formation position to a position where the aluminum film does not exist, penetration of the barrier layer can be suppressed.

[0010]

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

FIG. 1 is a front sectional view showing an embodiment of the present invention. An interdigital electrode (not shown) and a pad 11 for connection to an external circuit are formed on the surface of a piezoelectric substrate 10 such as a quartz crystal by vapor deposition and etching. The thickness of this aluminum film 11 is about 800 to 15,000 mm.

On the surface of this aluminum film 11, a chromium layer 12 is formed as a first barrier layer by the same means. The thickness of the chromium layer 12 is about 1000 to 4000 mm. Then, a nickel layer 13 is formed thereon as a second barrier layer. The thickness of the nickel layer 13 is set to about 2000-10000 mm.

By forming a thin gold film 14 on the surfaces of the barrier layers 12 and 13 formed as two layers, the barrier layer becomes an antioxidant film. The thickness of this gold layer 14 is about 500 to 1500 mm,
It is thinner than other layers. If a gold bump is formed on the surface of the gold layer 14, the adhesion between the bump and the electrode pad can be increased. Note that the material forming the bumps may not be gold.

FIG. 2 is a front sectional view showing another embodiment of the present invention. The formation of the aluminum layer 21, the chromium layer 22, the nickel layer 23, and the gold layer 24 on the surface of the substrate 20 is the same, except that the position of the upper three layers is shifted from the position of the aluminum layer 21. In this case, the bump can be formed at a position where aluminum does not exist below, so that a metal compound of the bump material and aluminum is less likely to be formed.

FIG. 3 is a graph comparing the strength of a conventional surface acoustic wave device having a bump connection with an electrode structure and the surface acoustic wave device according to the present invention. There is. Indicated by () are those according to the present invention, in which the strength is hardly deteriorated even when the temperature is increased, and the variation is small. △ indicates three layers of aluminum-chromium-gold
Above 300 ° C., the strength deteriorated. × indicates the case where aluminum is used alone, the strength is reduced by half from about 250 ° C, and is hardly usable above 300 ° C.

As described above, the die shear strength after bump formation and face-down bonding is less deteriorated, and stable quality can be obtained.

[0017]

According to the present invention, it is possible to obtain a surface acoustic wave device capable of preventing the generation of dissimilar metal compounds, maintaining the mechanical strength, and maintaining a large adhesive strength in face-down bonding.

In addition, since a bonding pad having stable quality can be obtained, a highly reliable surface acoustic wave device having not only mechanical characteristics but also excellent electrical characteristics can be obtained.

Further, since a gold layer is formed on the surface,
There is also an advantage that good adhesion with the gold bump can be maintained, and low power and low load can be achieved even under processing conditions.

[Brief description of the drawings]

FIG. 1 is a front sectional view showing an embodiment of the present invention.

FIG. 2 is a front sectional view showing another embodiment of the present invention.

FIG. 3 is an explanatory diagram of the strength of the surface acoustic wave device according to the present invention.

[Explanation of symbols]

 10:20: substrate 11, 21: aluminum layer 12, 22: chromium layer 13, 23: nickel layer 14, 24: gold layer

Claims (3)

[Claims] 1. A surface acoustic wave device comprising an aluminum interdigital electrode and an electrode pad for connecting the interdigital electrodes to an external circuit, wherein the surface acoustic wave device is face-down bonded by a bump connected to the electrode pad. A surface acoustic wave device comprising: a chromium layer on all or part of the surface; and a nickel layer formed on the surface of the chromium layer, and a gold electrode layer formed on the surface of the nickel layer. 2. A surface acoustic wave device comprising an aluminum interdigital electrode and an electrode pad for connecting them to an external circuit, wherein the surface acoustic wave device is face-down bonded by a bump connected to the electrode pad. It has a chromium layer on all or part of the surface and a nickel layer formed on the surface of the chromium layer, a gold electrode layer is formed on the surface of the nickel layer, and a pump is formed on the surface. Surface acoustic wave device. 3. The surface acoustic wave device according to claim 1, wherein the chromium and nickel layers are drawn out to a position where aluminum does not exist, and the bump is formed on a surface where aluminum does not exist.