Wave transmission lines and networks – Coupling networks – Electromechanical filter
Reexamination Certificate
2001-01-16
2002-12-24
Lee, Benny (Department: 2817)
Wave transmission lines and networks
Coupling networks
Electromechanical filter
C333S192000, C156S327000, C156S338000
Reexamination Certificate
active
06498547
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an anisotropically electroconductive adhesive and a ladder filter using it. More specifically, it relates, for example, to an anisotropically electroconductive adhesive which is electroconductive in the direction of thermocompression bonding but is insulative in the other directions, and to a ladder filter using it.
2. Description of the Related Art
It is known that an electroconductive adhesive is used for conventionally bonding an external electrode formed on an piezoelectric resonator to a land formed on an insulating substrate in a ladder filter, that is, a piezoelectric part in which plural piezoelectric resonators utilizing mechanical resonance of a piezoelectric material are used (cf. Japanese Unexamined Patent Application Publication No. 11-168348).
The structure of this ladder filter will be explained.
FIG. 1
is a top plan view showing an example of a ladder filter as disclosed in Japanese Unexamined Patent Application Publication No. 11-168348.
FIG. 2
is its front view. A known insulating substrate such as a glass epoxy substrate or an alumina substrate is used as the insulating substrate b.
On one of the main surfaces of the insulating substrate b, four pattern electrodes c
1
, c
2
, c
3
and c
4
are formed with specific distances therebetween. On these pattern electrodes c
1
through to c
4
, five lands e
1
, e
2
, e
3
, e
4
and e
5
are formed in line and with specific distances therebetween, wherein each of the lands e
1
through to e
4
is formed on one end of each of the pattern electrodes c
1
through to c
4
, and the land e
5
is formed on the other end of the pattern electrode c
2
.
On the lands e
1
through to e
5
of these pattern electrodes c
1
through to c
4
, four piezoelectric resonators a
1
, b
1
, b
2
and a
2
are aligned in line and in this order, wherein the two piezoelectric resonators a
1
and a
2
are used as serial resonators having the same structure, and the other two piezoelectric resonators b
1
and b
2
are used as parallel resonators having the same structure as shown in FIG.
3
.
Furthermore, in this ladder filter, the central portion in the lengthwise direction (in the up/down direction on the surface of
FIG. 1
) of an external electrode f
1
of the piezoelectric resonator a
1
which is to be the first serial resonator, is bonded to the land e
1
of the pattern electrode c
1
with an electroconductive adhesive d. Thereby, the external electrode f
1
of the piezoelectric resonator a
1
is connected to the pattern electrode c
1
.
Also, the central portion in the lengthwise direction of an external electrode f
2
of the piezoelectric resonator a
1
, and the central portion in the lengthwise direction of an external electrode f
1
of the piezoelectric resonator b
1
which is to be the first parallel resonator, are bonded to the land e
2
of the pattern electrode c
2
with the electroconductive adhesive d. Thereby, the external electrode f
2
of the piezoelectric resonator a
1
and the external electrode f
1
of the piezoelectric resonator b
1
are connected to the pattern electrode c
2
.
Furthermore, the central portion in the lengthwise direction of an external electrode f
2
of the piezoelectric resonator b
1
, and the central portion in the lengthwise direction of an external electrode f
1
of the piezoelectric resonator b
2
which is to be the second parallel resonator, are bonded to the land e
3
of the pattern electrode c
3
with the electroconductive adhesive d. Thereby, the external electrode f
2
of the piezoelectric resonator b
1
and the external electrode f
1
of the piezoelectric resonator b
2
are connected to the pattern electrode c
3
.
Also, the central portion in the lengthwise direction of an external electrode f
2
of the piezoelectric resonator b
2
, and the central portion in the lengthwise direction of an external electrode f
1
of the piezoelectric resonator a
2
which is to be the second serial resonator, are bonded to the land e
4
of the pattern electrode c
4
with the electroconductive adhesive d. Thereby, the external electrode f
2
of the piezoelectric resonator b
2
and the external electrode f
1
of the piezoelectric resonator a
2
are connected to the pattern electrode c
4
.
Furthermore, the central portion in the lengthwise direction of an external electrode f
2
of the piezoelectric resonator a
2
is bonded to the land e
5
of the pattern electrode c
2
with the electroconductive adhesive d. Thereby, the external electrode f
2
of the piezoelectric resonator a
2
is connected to the pattern electrode c
2
.
However, as miniaturization of products has accompanied a shortened distance between the lands formed on an insulating substrate, there is danger, with the conventional electroconductive adhesive, that an electroconductive adhesive spills out or exudes out of the adhesion area on heating and pressing, easily entailing short circuitry between the lands. Thereupon, in the course of the investigation related to the present invention, bonding with an anisotropically electroconductive adhesive was investigated for preventing this short circuitry between the lands.
The anisotropically electroconductive adhesive for use herein is a thermosetting insulating adhesive with which electroconductive particles are blended. Accordingly, by interposing an anisotropically electroconductive adhesive between an electronic part such as a circuit board and another electronic part such as a circuit board for thermocompression bonding, the electroconductive particles are contacted with one another in the direction of thermocompression to electrically connect both electronic parts, while both electronic parts are connected mechanically with the thermosetting insulating adhesive. On the other hand, the electroconductive particles are not contacted with one another in the directions other than the direction of compression bonding, resulting in an insulated state.
When such a thermosetting, anisotropically electroconductive adhesive interposes and is thermocompressed between both electronic parts, the curing agent causes a curing reaction to cure the thermosetting resin and to bond both electronic parts. In many cases, an epoxy type thermosetting resin is used for the thermosetting insulating adhesive. To be more specific, an epoxy resin in combination with a curing agent for an epoxy resin selected from the group of various materials consisting of a polyamide resin, an amine resin, an imidazole resin, a melamine resin, an anhydride, etc., is used.
However when a conventional anisotropically electroconductive adhesive was used for bonding a piezoelectric resonator to a pattern electrode on an insulating substrate, a problem of degraded filter characteristics would occur in a ladder filter shown in FIG.
1
. It was found in the course of the investigation related to the present invention, that it was caused by the vibration of the piezoelectric resonator propagated through the anisotropically electroconductive adhesive to the insulating substrate, which was then propagated to another piezoelectric resonator.
Thus, one of the main objects of this invention is to provide an anisotropically electroconductive adhesive which furnishes good filter characteristics without allowing the vibration of a piezoelectric resonator to be propagated to the insulating substrate, in the connection of the piezoelectric resonator with a pattern electrode on the insulating substrate.
Another object of the present invention is to provide a ladder filter having good filter characteristics, by using such an anisotropically electroconductive adhesive.
SUMMARY OF THE INVENTION
One aspect of the present invention is an anisotropically electroconductive adhesive comprising a thermosetting insulating adhesive mixed with electroconductive particles, the thermosetting insulating adhesive having an intrinsic acoustic impedance of about 1.4 MPa·s/m or less.
It is preferable that the thermosetting insulating adhesive in such an anisotropically electroconductive adhesive h
Dickstein Shapiro Morin & Oshinsky LLP.
Lee Benny
Murata Manufacturing Co. Ltd.
Summons Barbara
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