Electrical generator or motor structure – Non-dynamoelectric – Piezoelectric elements and devices
Reexamination Certificate
2003-04-16
2004-08-17
Mis, David (Department: 2817)
Electrical generator or motor structure
Non-dynamoelectric
Piezoelectric elements and devices
Reexamination Certificate
active
06777858
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a ceramic package mounted with a crystal oscillator functioning as a frequency generator and a frequency modulator. In particular, the structure of the ceramic package is improved in order to reduce its size while minimizing thermal influence to a crystal wafer mounted on the ceramic package.
2. Description of the Related Art
A crystal oscillator is generally used in various forms such as a frequency generator, a frequency modulator and a frequency converter. The crystal oscillator utilizes crystal having excellent piezoelectric characteristics, in which crystal functions as a stable mechanical vibrator.
Crystal is artificially grown in a high pressure autoclave, and cut along a crystal axis into pieces of various sizes and shapes. A crystal piece is formed into the shape of a wafer. The crystal wafer is necessarily formed to have a low phase noise, a high Q value and a low change rate of frequency according to time and environmental change.
The crystal wafer is fixed in a package and electrodes are formed on the crystal water for electrical connection so as to be used as a crystal oscillator. The crystal wafer is electrically connected to external electric devices and bonded to the package via conductive adhesive to this end, in which sufficient bonding areas are needed to obtain excellent vibration efficiency of the crystal oscillator and its reliability against external impact.
Sealing is provided to protect the crystal oscillator fixed to the package from external circumstances and contaminating substances. Since the operating efficiency of the crystal oscillator and its quality are greatly influenced by external environmental change and contamination, the crystal package is preferably so sealed to have a very low leak rate. To this end, a metallic lid-supporting sheet is bonded to a top of the ceramic package, and a lid made of the same material as the lid-supporting sheet is placed on the lid-supporting sheet and sealed thereto via electric welding. It is important that ceramic-to-metal and metal-to-metal bonding areas are airtight since external contaminating substances penetrated into the package may deteriorate several characteristics of the crystal oscillator such as reliability.
Peripheral devices are getting rapidly reduced in their sizes as personal portable terminals and radio apparatuses are miniaturized owing to ongoing development of mobile and radio communication apparatuses. On the other hand, the capacity of the crystal oscillator is enlarged, compared to those of the peripheral devices. Spatial restraints against the crystal oscillator are increased since electrical and mechanical connection of the crystal oscillator to the outside is restricted and miniaturization of the crystal wafer is limited. In particular, a crystal oscillator mounted on a temperature compensated crystal oscillator or TCXO package increases overall volume, and thus miniaturization of this crystal oscillator is getting more necessary. Accordingly, the art growingly requires a technique for miniaturizing the crystal oscillator and reducing its size.
FIG.
1
A and
FIG. 1B
are sectional and plan views of a conventional ceramic package for a crystal oscillator. In
FIGS. 1A and 1B
, the crystal oscillator ceramic package comprises a bottom sheet
11
constituting a bottom of the package and a buffer sheet
12
disposed on the bottom sheet
11
for supporting a crystal wafer
16
. The package also comprises an insulating sheet
13
on the buffer sheet
12
for obtaining a vibration space of the crystal oscillator as well as insulating the buffer sheet
12
. The bottom sheet
11
, the buffer sheet
12
and the insulating sheet
13
are commonly made of ceramic. Electrodes
18
are applied to a top of the buffer sheet
12
for electric connection of the crystal oscillator. The buffer sheet
12
serves to ensure stable oscillation of the crystal and protect the crystal wafer from external impact, and the electrodes function to connect between the crystal wafer and external terminals. The crystal wafer
16
is attached to the electrodes
18
of the buffer sheet
12
via conductive adhesive
19
and electrically connected to the same. A lid-supporting sheet
14
is formed on a top of the insulating sheet
13
to function as a cover of the ceramic package, and a lid
15
is formed on the lid-supporting sheet
14
for insulation of the ceramic package.
Since the conventional crystal oscillator ceramic package shown in
FIGS. 1A and 1B
comprises total five sheets from the bottom sheet to the uppermost lid, it is difficult to reduce the size of the ceramic package. Accordingly, the art has studied another crystal oscillator ceramic package with a structure improved over that of the above-described ceramic package.
FIG. 2
is a sectional view of another conventional ceramic package for a crystal oscillator. Referring to
FIG. 2
, buffer sheets
22
and
22
′ are formed on a bottom sheet
21
in the form of W or Mo deposited films at a thickness of about 10 &mgr;m. A top of the buffer sheet
22
is plated with metal such as Au, and a crystal wafer
26
is attached on the buffer sheet
22
via conductive adhesive
29
. An insulating sheet
23
is disposed around a top of the bottom sheet
21
to form a wall, and a supporting sheet
24
is formed on the insulating sheet
23
for supporting a lid
25
. The insulating sheet
23
is made of insulating ceramic to function as an insulator between the buffer sheet
22
and the supporting sheet
24
, and the supporting sheet
24
is made of a metallic material substantially identical with the lid
25
.
The crystal oscillator ceramic package having the structure shown in
FIG. 2
is reduced in the number of laminated sheets compared to the conventional ceramic package shown in
FIGS. 1A and 1B
. However, the bottom sheet is formed thicker than that of the ceramic package in
FIGS. 1A and 1B
. That is, since the thin buffer sheet is disposed on the bottom sheet and the crystal is attached on the buffer sheet, the bottom sheet is necessarily formed thick to protect the crystal from external impact or fracture, thereby causing difficulty in forming a ceramic package. Also, the thin buffer sheet affords poor stability to the crystal against external impact.
FIG. 3
is a sectional view of further another conventional ceramic package for a crystal oscillator disclosed in a Japanese Laid-Open Patent Application Serial No. 2000-124765, which pertains to a crystal oscillator and a fabricating process thereof. Referring to
FIG. 3
, the crystal oscillator comprises a crystal wafer
36
having electrodes, a supporting portion
22
for supporting the crystal wafer
36
, a first substrate
31
having conductor means for electrically connecting between the electrodes of the crystal wafer
36
and an external circuit, a second substrate
35
functioning as a cover and an insulating sheet
23
forming a side wall to enclose the crystal wafer
36
. The crystal oscillator also comprises glass balls
24
in the insulating sheet
23
.
In the crystal oscillator ceramic package shown in
FIG. 3
, the insulating sheet
23
is made of resin and melted to seal the package. Because the insulating sheet
23
made of resin may not uniformly maintain its height when it is melted, the glass balls
24
are previously disposed around the first substrate
31
before the insulating sheet
23
is melted in order tQ maintain the height of the insulating sheet
23
. The glass balls
24
are inevitably used in such a structure, thereby disadvantageously increasing the manufacturing cost of an article. Melting the insulating sheet
23
produces gas or fume to contaminate the crystal wafer or an inner region of the package thereby deteriorating the quality and reliability of the article.
SUMMARY OF THE INVENTION
The present invention has been made to solve the foregoing problems and it is therefore an object of the present invention to improve the structure of a ceramic package for a crystal oscillator i
Bang Shin Woong
Jun Hee Young
Kim Jong Tae
Lee Jong Pil
Seo Se Young
Lowe Hauptman & Gilman & Berner LLP
Mis David
Samsung Electro-Mechanics Co. Ltd.
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