Metal working – Piezoelectric device making
Reexamination Certificate
2001-12-27
2004-11-16
Tugbang, A. Dexter (Department: 3729)
Metal working
Piezoelectric device making
C029S594000, C029S840000, C029S843000, C228S180220, C310S363000
Reexamination Certificate
active
06817071
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a surface acoustic wave element having bump electrodes. More specifically, the present invention relates to a surface acoustic wave element having bump electrodes suitable for packaging while applying ultrasonic waves at joint portions thereof.
2. Description of the Related Art
In following recent trends toward miniaturization and thinning of electronic components, packaging of the electronic components via face-down bonding, where the functional surface of a surface acoustic wave element is packaged by arranging the functional surface so as to directly oppose to the packaging surface of a substrate, has been developed.
The general construction of the surface acoustic wave device packaged via face-down bonding is described with reference to
FIG. 1
to FIG.
3
.
FIG. 1
shows a plan view of a surface acoustic wave element.
FIG. 2
shows a cross section of the surface acoustic wave device in which the surface acoustic wave element is packaged.
FIG. 3
shows an enlarged cross section of a package of the surface acoustic wave element in the area of a bump electrode. As shown in
FIG. 1
, the surface acoustic wave element
12
includes a piezoelectric substrate
21
, a comb electrode
20
provided on the piezoelectric substrate
21
, where the comb electrode
20
is made of a conductive thin film primarily including Al, a reflector electrode
19
, an input electrode
16
, an output electrode
17
, and ground electrodes
18
. Among these electrodes, the input electrode
16
, the output electrode
17
, and the ground electrodes
18
also function as electrode pads for supplying a high frequency voltage. Referring to
FIG. 2
, the bump electrodes
11
are provided on the electrode pads
16
,
17
(not shown) and
18
. The surface acoustic wave element is connected to a package electrode
13
, which is provided on the package
14
, via the bump electrodes
11
.
The electrodes
16
to
20
provided on the piezoelectric substrate
21
are formed by patterning into a prescribed shape, via photolithography and etching, a metal thin film primarily made of Al having a thickness of about 0.1 to 0.2 &mgr;m, which is disposed on the substrate
21
by vacuum deposition or sputtering. Since these electrodes are simultaneously formed by vacuum deposition, the film thickness of the electrodes
16
to
18
, or of the electrode pads, is determined by the film thickness of the comb electrode
20
. In other words, when the comb electrode
20
is required to have a thickness of about 0.1 to 0.2 &mgr;m, the electrode pads
16
to
18
can not be formed to be thicker than the comb electrode. Accordingly, the electrode pads
16
to
18
are very weak. As such, when the bump electrodes
11
are directly formed on the electrode pads
16
to
18
having a thickness of 0.1 to 0.2 &mgr;m, and the surface acoustic wave element
12
is packaged on the package
14
via the bump electrodes
11
, sufficient bonding strength cannot be obtained causing, for example, peel-off of the electrode pads
16
to
18
.
As shown in
FIG. 3
, an intermediate electrode
22
, which is also primarily made of Al, has a thickness of about 1 &mgr;m and is provided via vacuum deposition or sputtering on the electrode pads
16
to
18
. Thus, sufficient bonding strength is achieved by providing an additional electrode layer on the electrode pads
16
to
18
. However, the surfaces of the electrode pads
16
to
18
are easily oxidized since they are made mainly of Al. Consequently, bonding strength between the electrode pads
16
to
18
and the intermediate electrode
22
is insufficient if the intermediate electrode
22
is also made of Al, and if directly provided on the electrode pads
16
to
18
having oxidized surfaces. Accordingly, a base electrode
23
made of Ti, which has good bonding strength with Al is provided at the bottom surface of the intermediate electrode
22
to ensure sufficient bonding strength between the electrode pads
16
to
18
and the intermediate electrodes
22
.
Accordingly, a thin layer made of Ti as the base electrode
23
is provided on the electrode pads
16
to
18
, an Al layer serves as the intermediate electrode
22
, the bump electrode
11
is provided on the intermediate electrode
22
, and the surface acoustic wave element is disposed at a position where the package electrode
13
is opposed to the bump electrode
11
. These components are packaged on the package
14
by press-bonding while applying ultrasonic waves or heat.
However, the conventional surface acoustic wave element as described above has the following problems. When the surface acoustic wave element
21
is arranged to be opposed to the package electrode
13
provided on the package
14
via the bump electrode
11
, and the package electrode
13
is press-bonded to the package electrode
13
while applying ultrasonic waves or heat, the joining portion of the bump electrode
11
of the surface acoustic wave element, or the electrode pads
16
to
18
and the intermediate electrode
22
located thereon, suffers from large stresses. Since bonding strength between the electrode pads
16
to
18
and the intermediate electrode
22
is enhanced by providing the base electrode
23
such as Ti having a high bonding strength with Al at the bottom of the intermediate electrode
22
, the stress generated in bonding the package electrode
13
to the bump electrode
11
becomes concentrated on the piezoelectric substrate
21
at the bottom of the electrode pads
16
to
18
, not at the joint portion between the electrode pads
16
to
18
and the intermediate electrode
22
. Consequently, cracks and breakage are caused on the piezoelectric substrate
21
, which cause breakage of elements, decreased bond strength between the elements and the package
14
, and breakdown of electrical continuity.
SUMMARY OF THE INVENTION
To overcome the problems described above, preferred embodiments of the present invention provide an apparatus and method of manufacturing a surface acoustic wave element that does not have the problems of breakage of elements, decreased bond strength between the elements and the package, or breakdown of electrical continuity when the surface acoustic wave element is arranged opposite to the package electrode while applying ultrasonic waves or heat.
In a preferred embodiment of the present invention, an electronic element includes a substrate with an electrode pad thereon, a base electrode provided on the electrode pad, an intermediate electrode provided on the base electrode, and a bump electrode provided on the intermediate electrode, wherein the base electrode includes a metallic material that reduces orientation of the intermediate electrode.
In another preferred embodiment of the present invention, a surface acoustic wave element includes a piezoelectric substrate, a comb electrode on the piezoelectric substrate, electrode pads on the piezoelectric substrate, base electrodes provided on the electrode pads, intermediate electrodes provided on the base electrodes, bump electrodes provided on the intermediate electrodes, wherein the bump electrodes are made of a metal having a melting point of about 450° C. or more. Further, the base electrodes include a metallic material that reduces orientation of the intermediate electrodes.
In another preferred embodiment of the present invention, a method of packaging an electronic element includes the steps of providing a piezoelectric substrate, forming electrode pads on the piezoelectric substrate, disposing base electrodes on the electrode pads, disposing intermediate electrodes on the base electrodes, forming bump electrodes on the intermediate electrodes, wherein the bump electrodes are made of a metal having a melting point of about 450° C. or more, and disposing the electronic element on a package such that a bump electrode opposes a package electrode and press-bonding the package electrode to the bump electrode while applying ultrasonic waves or heat. Further, the base electrodes include a
Keating & Bennett LLP
Murata Manufacturing Co. Ltd.
Nguyen Donghai D.
Tugbang A. Dexter
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