Piezoelectric vibrator

Details Piezoelectric vibrator Piezoelectric vibrator

2000-02-22

2002-05-28

Sircus, Brian (Department: 2839)

Electrical generator or motor structure

Non-dynamoelectric

Piezoelectric elements and devices

C310S366000

Reexamination Certificate

active

06396201

ABSTRACT:

TECHNICAL FIELD
The present invention relates to the support of a piezoelectric vibrating reed and the constitution of a container in a piezoelectric vibrator.
BACKGROUND ART
A piezoelectric vibrator, such as a quartz resonator, is often supported in a box-type airtight container made of material, such as ceramic. Some piezoelectric vibrators sealed in box type containers are called surface mounted type (SMD type) vibrators. These vibrators are suitable for being mounted on printed circuit boards of electronic equipment and are often used as clock sources or the like in telecommunication equipment, portable electronic equipment, etc. A piezoelectric vibrating reed to be used for the vibrators is, for example, a strip rectangular plate type AT cut quartz vibrating reed, the outline of which is shown in a perspective view of FIG.
2
. In
FIG. 2
, reference numeral
1
is a quartz vibrating reed, and reference numeral
11
is a quartz vibrating reed electrode film. A similar electrode film is provided on a back surface of the quartz vibrating reed
1
. Reference numerals Ill and
121
are electrode lead lines of these electrode films. These lines are arranged in such a manner that they extend over both surfaces of an end of the quartz vibrating reed
1
.
An example of a box type container for SMD type vibrators is composed of a lower case
2
shown in an exploded perspective view of
FIG. 3 and a
lid
5
shown in a perspective view of FIG.
4
. The lower case
2
is a lamination of a first insulating substrate
21
and a second insulating substrate
22
, both of which are made of ceramic. The first insulating substrate
21
is provided as a pattern in which bottom surface electrode terminals
211
for SMD type vibrators, and wiring patterns
213
connected with the bottom surface electrode terminals
211
by side surface patterns
212
and having through hole connecting sections
214
at important points, are metallized on a bottom surface.
On a top surface of the second insulating substrate
22
, four terminals
221
for vibrating reeds are provided as metallized patterns. By means of a through hole (not shown in the drawings) provided within the top surface, the terminals
221
for vibrating reeds are connected with the wiring patterns
213
provided on the first insulating substrate
21
. With regard to the four terminals
221
for vibrating reeds, two each are adjacent and the terminals which face each other in a longitudinal direction are connected. The quartz vibrating reed
1
is mounted on the lower case
2
and the electrode lead lines
111
and
121
of the quartz vibrating reed
1
are arranged on the terminals
221
for vibrating reeds. In such a position, the electrode lead lines
111
and
121
are adhered with a conductive adhesive, thereby simultaneously achieving continuity and support. At this time, it does not matter whether the quartz vibrating reed
1
is on the right side or wrong side, or what direction the longitudinal direction faces. The lid
5
is put on the lower case
2
where the quartz vibrating reed
1
is mounted, and the peripheral bottom surface is airtightly sealed utilizing the lower case
2
and glass having a low melting point. A hole
222
provided at the second insulating substrate
22
functions so that the lower case
2
does not touch the center of the quartz vibrating reed
1
which has a great vibration amplitude. Further, center grooves
223
are provided so as to avoid a short circuit of the adjacent conductive adhesives. Detailed constitution of the box type container described above is basically the same as that disclosed in Japanese Patent Application No. Hei 7-316064.
There are roughly two kinds of methods of supporting a piezoelectric vibrating reed. One (1) is a center supporting method where both of two short edges of a piezoelectric vibrating reed are glued to a lower case with a conductive adhesive or conductive and nonconductive adhesives. The other (2) is a cantilever supporting method where among the two short edges, only the edge where electrode lead lines are provided is glued to the lower case (the terminals
221
for vibrating reeds provided at the upper part of the lower case) with a conductive adhesive, and the other short edge is left not glued. For the purposes of supporting a piezoelectric vibrating reed so that the vibrating reed has sufficient strength to bear an impulse and avoiding a harmful influence of the stress (or distortion) caused by the support upon vibration of the piezoelectric vibrating reed, various proposals for improving both the supporting methods have been made heretofore.
The center supporting method (1) described above has the advantages that impact resistance sufficient to avoid damage of the piezoelectric vibrator can be obtained and a thin container can be used because the piezoelectric vibrating reed is stationary. However, it also has disadvantages as follows: due to a shrinkage caused by curing of an adhesive (heat treatment for hardening) or a difference in thermal expansion coefficient between the piezoelectric vibrating reed and a substrate of the container or an adhesive, a residual stress arises inside the piezoelectric vibrating reed of the completed piezoelectric vibrator, whereby it tends to cause such problems that an oscillation frequency differs from a target value, the temperature characteristic of the frequency and the temperature characteristic of a comfort index (CI) become turbulent, or spuriousness arises. In order to avoid these problems, in Japanese Utility Model Laid-Open Publication No. Hei 1-143516, it has been proposed that a nonconductive adhesive having a small shrinkage factor is applied to a bottom surface of each short edge of the vibrating reed so as to pass through the center support and a conductive adhesive (which generally has a large shrinkage factor) is applied to a top surface of each short edge of the vibrating reed, whereby the deterioration of characteristic which may be caused by the residual stress can be prevented. Further, in Japanese Utility Model Laid-Open Publication No. Hei 5-18121, it has been proposed that one of the short edges of the piezoelectric vibrating reed is supported by a conductive adhesive (having great hardness) and a soft silicon adhesive is applied to the other one of the short edges, whereby residual distortion is reduced or various stresses are absorbed.
In the cantilever supporting method (2) described above, the influence of stress resulting from the support upon the vibration of the piezoelectric vibrating reed may be considered negligible. However, since the cantilever piezoelectric vibrating reed is used, when a strong impulse is applied to the piezoelectric vibrator as it stands, there is a great risk of peeling of adhered parts, breaking the piezoelectric vibrating reed, or the like. In order to avoid such problems, there is a constitution such that a stopper to restrict displacement of the piezoelectric vibrating reed is provided near a short edge which is free from support. As a concrete example, Japanese Patent Laid-Open Publication No. Hei 8-330886 has disclosed a constitution in which a bolster section and a buffer section to serve as stoppers are arranged on the short edge so as not to be adhered. Further, Japanese Patent Laid-Open Publication No. Hei 8-186457 has disclosed the following art: a first adhesive is applied to a cantilever holding section of a quartz vibrating reed and temporary curing is applied to the adhered section in such a manner that the solvent splashes; the quartz vibrating reed is placed on the section and a second adhesive is applied thereto; by curing the section entirely in the manner described above, shrinkage caused by the adhesive curing is properly controlled; and by slightly lifting the other edge of the quartz vibrating reed which is not adhered up from a substrate, an adequate space is obtained between a surface of the substrate to be a stopper and the aforementioned other edge of the quartz vibrating reed.
Problems of the above-mentioned concrete examples of improvement

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