JPH10313227A - Surface acoustic wave device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a surface acoustic wave device having high reliability and excellent shock-resistance and environment-resistance. SOLUTION: Electrode lands 12a, 12b and a junction land 11 formed on a base substrate 10 are formed on a sintered alumina substrate that is printed with conductive electrode paste and then sintered by the method of plating or the like of Ni/Au. An alloy AgPd is used for an electrode film formed on an electrode film at a lowermost layer of the electrode lands 12a, 12b, that is, an electrode film formed on an alumina base, and Ag is used for the electrode film of the lowermost layer of the junction land 11.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a surface acoustic wave device in which a SAW element mounted on a base substrate by solder bump connection is sealed in a package formed by soldering the base substrate and a cap. About.

[0002]

2. Description of the Related Art Conventionally, there has been known a surface acoustic wave device in which a SAW element is mounted on a base substrate by solder bump connection, and the base substrate and a metal cap are soldered to seal the SAW element. As a base substrate of such a surface acoustic wave device, a ceramic substrate such as alumina is used, and on one main surface thereof, an annular bonding land for performing solder bonding with a metal cap, and a soldering land for soldering a SAW element. A plurality of electrode lands and an electrode pattern such as an extraction electrode for connecting the electrode lands to achieve desired electrical connection are formed. In addition, one main surface of the SAW element has IDT, ID
A plurality of extraction electrodes extracted from T, and a bump electrode is formed at the tip of each extraction electrode. Then, each bump electrode of the SAW element is soldered (solder bump connection) to an electrode land on the base substrate, and the SAW element is supported and fixed to the base substrate and electrically connected to cover the SAW element. A metal cap is soldered to the joint land of the base substrate.

The electrode patterns such as the electrode lands and the joint lands are formed by printing and firing a conductive electrode material paste on a fired ceramic substrate, and then performing Ni plating / Au plating thereon. In the conventional surface acoustic wave device, the lowermost electrode film of the electrode lands and the bonding lands, that is, the electrode film formed on the base substrate is made of one of Ag and AgPd. I was

[0004]

However, in the case of using Ag as the lowermost electrode film of the electrode pattern,
There is a problem that the electrode lands are peeled off from the base substrate due to a drop impact on the product. Further, in the case of using AgPd, in a pressure cooker test (PCT) or a moisture resistance test, there is a problem that airtightness at a solder joint between the base substrate and the metal case cannot be maintained, resulting in poor characteristics. . The occurrence of such a problem is caused by Ag
Is weak in adhesion strength to ceramic substrates such as alumina.
gPd is caused by poor airtightness with the ceramic substrate.

It is an object of the present invention to provide a highly reliable surface acoustic wave device which is excellent in environmental resistance such as impact resistance and moisture resistance.

[0006]

In order to achieve the above object, the invention according to claim 1 is directed to an S-shaped electrode having a bump electrode formed thereon.
The bump electrode and the electrode land are mounted on the base substrate made of ceramic on which the joining land and the electrode land are formed by solder bump connection, and a cap covering the SAW element is soldered to the joining land. A surface acoustic wave device in which the SAW element is sealed in a space formed by the base substrate and the cap.
The lowermost electrode film of the electrode lands is made of AgPd;
The lowermost electrode film of the joining land is made of Ag.

According to a second aspect of the present invention, in the surface acoustic wave device according to the first aspect, the lowermost electrode film of the electrode land and the lowermost electrode film of the joining land are formed by printing and firing an electrode paste. It is characterized by the following.

According to the above-described structure, AgPd having a strong adhesion strength to the base substrate is used for the lowermost electrode film of the electrode land for connecting the SAW element to the solder bump, and the solder bonding with the cap is performed. Since the lowermost electrode film of the joining land is made of Ag having good airtightness with the base substrate, even if a shock such as a drop impact is applied, the electrode land to which the SAW element is soldered is removed from the base substrate. It does not peel off, and the airtightness between the bonding land and the base substrate is maintained even in the PCT or the moisture resistance test, so that characteristic failure due to humidity or the like can be prevented.

In this structure, the lowermost electrode film of the electrode lands and the joint lands is formed by printing and firing, so that a particularly effective effect can be obtained.

[0010]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A surface acoustic wave device according to the present invention will be described below with reference to FIGS. FIG. 1 is a sectional view of a surface acoustic wave device, and FIG. 2 is a plan view of a base substrate.

In this surface acoustic wave device, as shown in FIG. 1, the bump electrode 25 of the SAW element 20 is soldered to the electrode lands 12a and 12b of the base substrate 10, and the SAW element 20 is connected to the base substrate. The metal cap 30 having an open surface on one side is soldered to the joining land 11 of the base substrate 10 by solder 52 at its flange portion 31 so as to be supported and fixed to and electrically connected to the SAW element 20 so as to cover the SAW element 20. The SAW element 20 is sealed in a space formed by the base substrate 10 and the metal cap 30.

The base substrate 10 is made of alumina ceramic. On the upper surface thereof, as shown in FIG. 2, a square annular bonding land 11 for performing solder bonding with a metal cap 30 and a SAW element 20 are soldered. Electrode lands 12a, 12b for connection and extraction electrodes 13a, 1 connected to the electrode lands 12a, 12b to achieve desired electrical connection.
An electrode pattern made of 3b or the like is formed. Although not shown, an input / output terminal electrode and a ground terminal electrode are formed on the lower surface of the base substrate 10, and the lead electrode 13a is connected to the input / output terminal electrode, and the lead electrode 13b is connected to the ground terminal electrode by through holes or the like. I have. The electrode land 12b is a land for grounding, and the extraction electrode 13b drawn from the electrode land 12b is connected to the joint land 11 in order to improve the circumference of the ground.

The SAW element 20 has a surface wave substrate having a rectangular planar shape. An IDT, a reflector electrode, a plurality of extraction electrodes extracted from the IDT, and a bump at the tip of each extraction electrode are provided on the lower surface in FIG. The electrodes 25 are formed, and the face on which the bump electrodes 25 and the like are formed is a lower surface, that is, the bump electrodes 25 and the electrode lands 12a formed on the base substrate 10 corresponding to the bump electrodes 25 are used as lower surfaces.
12b are connected and fixed by the solder 51 and mounted on the base substrate 10. The metal cap 30 has a shape opened downward, and the base substrate 10 is formed all around the opening.
A flange portion 31 extending in parallel with the flange portion 31 is formed, and the flange portion 31 is soldered to the joint land 11 of the base substrate 10 by solder 52.

The electrode lands 12a and 12b and the bonding lands 11 formed on the base substrate 10 are formed by printing and firing a conductive electrode paste on a fired alumina substrate.
Ni / Au is formed thereon by plating or the like. In the present embodiment, the electrode lands 12
AgPd is used for the lowermost electrode film of a and 12b, that is, the electrode film formed on the alumina substrate, and Ag is used for the lowermost electrode film of the joint land 11.

Specifically, first, the electrode lands 12a, 12a
AgPd paste is screen-printed on the base substrate 10 using the pattern corresponding to the connection land 11b and the extraction electrodes 13a and 13b.
gPd is screen printed and then fired to make AgPd
And an Ag electrode film are formed. Next, a Ni film is formed on each of the electrode films and an Au film is formed on the Ni film by a method such as plating.

The Ni film is provided to prevent AgPd and Ag from being soldered, and the Au film is provided to improve solderability. These Ni film / Au film are formed as needed, and are not always necessary, and the material is not limited to Ni and Au. The printing order of AgPd and Ag is not particularly limited, and an Ag paste may be printed on the extraction electrodes 13a and 13b.

Preliminary solder (solder bumps) is previously provided on the electrode lands 12a and 12b and the joint lands 11, and the connection and joining of the SAW element 20 and the metal cap 30 to the base substrate 10 are performed by a reflow soldering method. Done. Although not shown, a solder flow prevention coat is usually formed by printing or the like so as to cover the extraction electrodes 13a and 13b. The surface acoustic wave device is used by being mounted on a mounting substrate with the lower surface of the base substrate 10 as a mounting surface.

As described above, in the surface acoustic wave device of this embodiment, the base substrate 1 is provided on the lowermost electrode film of the electrode lands 12a and 12b for soldering and fixing the SAW element 20.
AgPd, which has a strong adhesion strength to zero, is used, and the electrode lands 12a and 12b do not peel off from the base substrate 10 even when an impact such as a drop impact is applied. Further, Ag, which has good airtightness with the base substrate 10, is used for the lowermost electrode film of the bonding land 11 that is solder-bonded to the metal cap 30, so that it is exposed to a poor environment of high temperature and high humidity. The characteristics do not deteriorate. Note that the area of the bonding land 11 is large, and even if Ag is used, the bonding land and the base substrate can have a necessary and sufficient adhesion strength.

For the conventional surface acoustic wave device and the surface acoustic wave device of the present embodiment, a drop impact test (5000 G)
As a result of comparison at CT (121 ° C., 2 atm, humidity 100%) (sample number n = 20), in the case of the conventional AgPd product, one characteristic failure was recognized in PCT177 hours, and the conventional Ag product was observed. In the drop impact test, peeling of five electrode lands was observed. On the other hand, in the surface acoustic wave device of the present example, the characteristic failure in the PCT and the peeling of the electrode land in the drop impact test did not occur.

Incidentally, the electrode pattern formed on the base substrate is not limited to the above-described embodiment.
A dummy electrode land may be formed.
The extraction electrode extracted from the ground electrode land does not necessarily need to be connected to the joining land.

[0021]

As described above, in the surface acoustic wave device according to the present invention, the lowermost electrode film of the electrode land for connecting the SAW element to the solder bump is made of AgPd having strong adhesion strength to the base substrate. Since the lowermost electrode film of the joint land for performing the solder joint with the cap is made of Ag having good airtightness with the base substrate, the electrode land can be removed from the base substrate by an impact such as a drop impact. Can be prevented, and the airtightness between the bonding land and the base substrate can be maintained even in the PCT or the moisture resistance test, and the characteristic deterioration due to humidity or the like can be prevented.

Therefore, according to the present invention, a highly reliable surface acoustic wave device excellent in impact resistance and environmental resistance can be obtained.

[Brief description of the drawings]

FIG. 1 is a sectional view of a surface acoustic wave device according to one embodiment of the present invention.

FIG. 2 is a plan view of a base substrate of the surface acoustic wave device according to one embodiment of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 10 Base board 11 Joining land 12a, 12b Electrode land 20 SAW element 25 Bump electrode 30 Metal case 31 Flange part

Claims (2)

[Claims] 1. A SAW device on which bump electrodes are formed,
The bump land and the electrode land are connected by solder bump connection and placed on a base substrate made of ceramic on which the bonding land and the electrode land are formed, and a cap covering the SAW element is soldered to the bonding land. In a surface acoustic wave device in which the SAW element is sealed in a space formed by the base substrate and the cap, a lowermost electrode film of the electrode land is made of AgPd,
A surface acoustic wave device, wherein the lowermost electrode film of the joining land is made of Ag. 2. The surface acoustic wave device according to claim 1, wherein the lowermost electrode film of the electrode lands and the lowermost electrode film of the joining lands are formed by printing and firing an electrode paste.