Electrical generator or motor structure – Non-dynamoelectric – Piezoelectric elements and devices
Reexamination Certificate
2001-08-21
2002-09-17
Dougherty, Thomas M. (Department: 2834)
Electrical generator or motor structure
Non-dynamoelectric
Piezoelectric elements and devices
C310S364000, C310S348000, C029S025350
Reexamination Certificate
active
06452311
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of Invention
The present invention relates to structures of piezoelectric devices, such as piezoelectric resonators or piezoelectric oscillators, having a piezoelectric resonator element accommodated in a package, and to manufacturing methods therefor.
2. Description of Related Art
FIGS.
8
(
a
) and
8
(
b
) show an example of a conventional piezoelectric resonator, and for the convenience of understanding, a lid body thereof is omitted in the figures. FIG.
8
(
a
) is a plan view showing the interior of the piezoelectric resonator by removing the lid body, and FIG.
8
(
b
) is a schematic cross-sectional view showing the interior taken along plane A-A (shown in FIG.
8
(
a
)) by removing the lid body.
In FIGS.
8
(
a
) and
8
(
b
), a piezoelectric resonator
10
has a package base
12
in the form of a box in which a space portion
13
is formed for accommodating a piezoelectric resonator element
11
in the form of a plate. One end
11
a
of the piezoelectric resonator element
11
is fixed on gold-plated electrodes
14
and
14
, which are two mounting electrodes disposed on a step
19
formed in the space portion
13
, by bonding using silicone-based conductive adhesives
15
and
15
, and the other end
11
b
is a free end.
In this structure, the piezoelectric resonator element
11
is formed of, for example, quartz crystal, and on the surface thereof, electrodes (not shown) are formed which apply a driving voltage to the quart crystal for performing a predetermined oscillation. As a material for the lid body, which is not shown, for sealing the package base
12
, a metal, such as Koval, or a ceramic, such as alumina, is used.
As a material for the package base
12
, a ceramic, such as alumina, is used, and in the case shown in FIG.
8
(
b
), on a first base material
16
in the form of a flat plate, a second base material
17
, having an opening formed therein, is placed, and in addition, a third base material
18
, having an opening formed therein, which is larger than the opening in the second base material, is placed thereon. Furthermore, on the third base material
18
, a seam ring
18
a
is disposed. Accordingly, the package base
12
has the space portion
13
formed therein, so that the piezoelectric resonator element
11
can be accommodated, and in addition, the step
19
is formed for bonding the piezoelectric resonator element
11
thereto.
The mounting electrodes
14
and
14
on the surface of the step
19
are connected to external terminals
14
a
, which are exposed outside the package base
12
via conduction paths
14
b
passing through the layered structure formed of the laminated base materials.
Accordingly, a driving voltage from the external terminals
14
a
is applied to electrodes, which are formed on the surface of the piezoelectric resonator element
11
via the mounting electrodes
14
and
14
, and the piezoelectric resonator element
11
oscillates at a predetermined frequency.
FIG. 9
is a flow chart generally showing steps of manufacturing the piezoelectric resonator
10
described above.
In
FIG. 9
, first, the package base
12
is formed using a ceramic material, such as alumina, and the mounting electrodes
14
and
14
are formed by, for example, plating so as to correspond to the piezoelectric resonator element
11
.
In this step, in order for the package base
12
to be formed as a laminated structure as described above, green sheets, formed of ceramic materials corresponding to individual layers, are formed for each layer, and are then laminated to each other, and firing is then performed.
For example,
FIG. 10
shows a green sheet including the second base material layers
17
shown in
FIG. 8
, and shows a state in which a plurality of the second layer base materials
17
are formed in one green sheet which is not yet cut. On the second base material layer
17
, for example, as shown in
FIG. 10
, the mounting electrode
14
, which is connected to the conduction path
14
b
, is formed by electroplating or a similar method. That is, after the individual layers are laminated to each other and are then fired, the seam ring
18
a
(shown in FIGS.
11
(
a
) and
11
(
b
)) is brazed thereto, and gold electroplating is performed on the external terminal
14
a
. In this step, as described above, since the mounting electrode
14
is connected to the external terminal
14
a
via the conduction path
14
b
, the mounting electrode
14
and the conduction path
14
b
are formed by gold (Au) plating on a tungsten metalized underlying layer at exposed areas thereof which have been laminated.
FIGS.
11
(
a
) and
11
(
b
) show the package base
12
formed of the individual base materials laminated to each other. FIG.
11
(
a
) is a plan view of the package base
12
, and FIG.
11
(
b
) is a schematic cross-sectional view taken along plane B—B (shown in FIG.
11
(
a
)).
As shown in FIGS.
11
(
a
) and
11
(
b
), when the third base martial
18
is placed on the second base material
17
, the conduction path
14
b
is located below the third base material
18
and is almost covered therewith, and the two mounting electrodes
14
and
14
are exposed on the step
19
.
Next, after the seam ring is brazed to the third base material
18
, gold plating is performed on the exposed mounting electrodes
14
and
14
described above.
Accordingly, only the mounting electrodes
14
and
14
, which are exposed, are plated with gold, and the conduction path passing through the layers is not plated with gold.
On the other hand, in
FIG. 9
, an excitation electrode and a connection electrode are formed by deposition on the piezoelectric resonator element
11
, and silicone-based conductive adhesives
15
and
15
are applied to the mounting electrodes
14
and
14
on which the piezoelectric resonator element
11
is to be mounted (ST
1
).
Next, on the mounting electrodes
14
and
14
of the package base
12
in
FIG. 8
, the piezoelectric resonator element
11
described above is fixed by bonding using the silicone-based conductive adhesives
15
and
15
, as shown in
FIG. 8
(ST
2
).
Next, the package base
12
is placed in a heat curing oven, which is not shown, and the silicone-based conductive adhesives
15
and
15
are dried and cured (ST
3
). Subsequently, when the piezoelectric resonator element
11
is sufficiently fixed on the mounting electrodes
14
and
14
with the silicone-based conductive adhesives
15
and
15
provided therebetween, a driving voltage from the external terminals
14
a
is applied to the piezoelectric resonator element
11
via the conduction paths
14
b
and the mounting electrodes
14
and
14
, and while the oscillation frequency is monitored, the weights of the electrodes are reduced by, for example, irradiating laser light on the surface of the piezoelectric resonator element
11
, whereby frequency adjustment is performed (ST
4
).
Next, the lid body, which is not shown, is placed on the package base
12
, and sealing is performed by, for example, seal welding (ST
5
).
As described above, the piezoelectric resonator
10
is complete.
Most of the steps described above are commonly used for a piezoelectric oscillator which is another piezoelectric device. That is, unlike the piezoelectric resonator, since the piezoelectric oscillator has an integrated circuit mounted in the package base, accordingly, the structure and the steps thereof are slightly different from those of the piezoelectric resonator.
FIGS.
12
(
a
) and
12
(
b
) show an example of a conventional piezoelectric oscillator, and for the convenience of understanding, a lid body thereof is omitted in FIGS.
12
(
a
) and
12
(
b
). FIG.
12
(
a
) is a plan view showing the interior of the piezoelectric oscillator by removing the lid body, and FIG.
12
(
b
) is a schematic cross-sectional view showing the interior taken along plane C—C (shown in FIG.
12
(
a
)) by removing the lid body.
In the figures described above, the same reference numerals of the piezoelectric resonator in
FIG. 10
designate constituents equivalent there
Dougherty Thomas M.
Oliff & Berridg,e PLC
Seiko Epson Corporation
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