Wave transmission lines and networks – Coupling networks – Electromechanical filter
Reexamination Certificate
2001-10-03
2004-03-23
Summons, Barbara (Department: 2817)
Wave transmission lines and networks
Coupling networks
Electromechanical filter
C310S31300R, C029S025350
Reexamination Certificate
active
06710682
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a surface acoustic wave device, a method for producing the same, and a circuit module using the same.
2. Description of the Related Art
Recently, communication equipment such as a mobile phone is being miniaturized and reduced in size rapidly. Along with this, there is a demand for miniaturization of a surface acoustic wave device (hereinafter, which may be referred to as a “SAW device”) such as a filter and a resonator mounted on communication equipment. There also is a demand for miniaturization of the space required for setting a SAW device.
FIG. 38
schematically shows a cross-sectional view (hatching is omitted) of a SAW device
900
as a representative example of a conventional SAW device. The SAW device
900
includes a piezoelectric substrate
901
, comb electrodes (alternatively called inter-digital transducers)
902
and electrode pads
903
formed on the piezoelectric substrate
901
, wires
904
, electrode pads
905
, internal electrodes
906
, external electrodes
907
, a layered ceramic substrate
908
composed of a layered body of ceramic substrates
908
a
,
908
b
, and
908
c
, and a cover portion
909
.
The comb electrodes
902
excite a surface acoustic wave. The comb electrodes
902
are connected electrically to the electrode pads
903
via wiring lines (not shown) formed on the piezoelectric substrate
901
. The comb electrodes
902
are connected electrically to the external electrodes
907
via the electrode pads
903
, the wires
904
, the electrode pads
905
, and the internal electrodes
906
. In the SAW device, it is required to form an enclosed space around the comb electrodes
902
for the purpose of ensuring propagation of a surface acoustic wave. In the SAW device
900
, the layered ceramic substrate
908
and the cover portion
909
form an enclosed space.
However, in the SAW device
900
, it is required to form wires
904
three-dimensionally, and enlarge the electrode pads
903
and
905
for wire bonding. Therefore, such a configuration of the SAW device
900
hinders miniaturization thereof. Furthermore, in the SAW device
900
, a parasitic inductance caused by the wires
904
is large.
In order to solve the above-mentioned problems, a method for mounting a SAW element provided with the piezoelectric substrate
901
, the comb electrodes
902
, and the electrode pads
903
onto a substrate by a facedown technique has been reported (see JP 5(1993)-55303 A).
FIG. 39
schematically shows a cross-sectional view (partial hatching is omitted) of a SAW device
950
as an example of such a SAW device. The SAW device
950
includes a piezoelectric substrate
901
, comb electrodes
902
and electrode pads
903
formed on the piezoelectric substrate
901
, bumps
951
, electrode pads
952
, internal electrodes
953
, external electrodes
954
, a substrate
955
, dams
956
, and a resin film
957
.
The comb electrodes
902
are connected electrically to the external electrodes
954
via the electrode pads
903
, the bumps
951
, the electrode pads
952
, and the internal electrodes
953
. On the periphery of the comb electrodes
902
, an enclosed space is provided by the resin film
957
formed so as to cover the piezoelectric substrate
901
. The dams
956
prevent resin from flowing into the enclosed space when the resin film
957
is formed. In the SAW device
950
, a SAW element is mounted on the substrate
955
by a face-down technique, so that the SAW device in this example is more likely to be miniaturized compared with the SAW device
900
.
There also is a method for mounting a SAW element in an air-tight container of the SAW device
900
by a face-down technique.
However, the SAW device
905
has the following problems. In order to produce the SAW device
950
, it is required to form the electrode pads
952
, the internal electrodes
953
, and the external electrodes
954
on the surface of and inside the substrate
955
. During this process, if the substrate
955
is thin, the substrate
955
may be warped or damaged. This makes it difficult to make the substrate
955
thin, resulting in insufficient miniaturization of an apparatus.
Furthermore, in the course of producing the SAW device
950
, the dams
956
prevent the resin to be the resin film
957
from flowing into the enclosed space. This requires that mounting is conducted while the interval between the piezoelectric substrate
901
and the substrate
955
is regulated with high precision. If the bumps
951
, the electrode pads
952
, and the internal electrodes
953
are mounted so as to be positioned in a line, it is difficult to conduct mounting with high precision. This is because the material for the internal electrode
953
is different from that for the substrate
955
. Therefore, in the SAW device
950
, the bumps
951
and the internal electrodes
953
are disposed so as to be shifted from each other, which makes it difficult to achieve sufficient miniaturization.
Furthermore, with a device in which a SAW element is mounted in an air-tight container of the SAW device
900
by a face-down technique, an airtight container capable of accommodating the SAW device is required. Therefore, even with such a device, sufficient miniaturization is difficult.
SUMMARY OF THE INVENTION
Therefore, with the foregoing in mind, it is an object of the present invention to provide a SAW device capable of being further miniaturized compared with a conventional SAW device, and a method for producing the same.
In order to achieve the above-mentioned object, a surface acoustic wave device of the present invention includes: a piezoelectric substrate; a plurality of comb electrodes for exciting a surface acoustic wave, disposed on a principal plane of the piezoelectric substrate; a plurality of bumps disposed on the principal plane; and a member containing resin, disposed on the principal plane side, wherein the bumps and the comb electrodes are connected electrically to each other, and at least a part of the bumps is buried in the member. The surface acoustic wave device of the present invention can be used, for example, for a frequency filter and a resonator mounted in communication equipment.
In the above-mentioned surface acoustic wave device, the member may be an insulating sheet, the insulating sheet may be disposed away from the comb electrodes, and the bumps may penetrate through the insulating sheet.
The above-mentioned surface acoustic wave device further includes a circuit board disposed so as to be opposed to the principal plane of the piezoelectric substrate, wherein the circuit board includes wiring lines formed on a surface on the piezoelectric substrate side, the member is disposed between the piezoelectric substrate and the circuit board, and the member is a space forming member for forming a space that allows the comb electrodes to vibrate on a periphery of the comb electrodes.
Furthermore, a first method for producing a surface acoustic wave device of the present invention includes the steps of: (a) forming a plurality of comb electrodes for exciting a surface acoustic wave and bumps connected electrically to the comb electrodes on a principal plane of a piezoelectric substrate; and (b) opposing the principal plane of the piezoelectric substrate to an insulating sheet, and bringing the piezoelectric substrate and the insulating sheet closer together so that the bumps penetrate through the insulating sheet.
Furthermore, a second method for producing a surface acoustic wave device of the present invention includes the steps of: (i) forming a piezoelectric substrate, a plurality of comb electrodes formed on a principal plane of the piezoelectric substrate, a surface acoustic wave element including a plurality of bumps connected electrically to the plurality of comb electrodes, and a circuit board having a principal plane on which wiring lines are formed; (ii) disposing the principal plane of the piezoelectric substrate and the principal plane of the circuit board so that they are opposed to each othe
Bessho Yoshihiro
Fujii Kunihiro
Moritoki Katsunori
Murakami Kouzou
Nanba Akihiro
Matsushita Electric - Industrial Co., Ltd.
Merchant & Gould P.C.
Summons Barbara
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