Electricity: conductors and insulators – Boxes and housings – Hermetic sealed envelope type
Reexamination Certificate
2002-08-27
2004-08-17
Reichard, Dean A. (Department: 2831)
Electricity: conductors and insulators
Boxes and housings
Hermetic sealed envelope type
C174S034000, C331S067000
Reexamination Certificate
active
06777613
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a multifunctional or multi-frequency quartz crystal unit in which a tuning fork type quartz crystal blank and a quartz crystal blank of thickness-shear mode are hermetically encapsulated in the single same container, and more particularly, relates to a multifunctional crystal unit using a crystal blank of AT cut as a thickness-shear mode crystal blank, and a method of manufacturing the same.
2. Description of the Background Arts
A quartz crystal unit is incorporated in an oscillator or an oscillating circuit as a reference source of frequency and time, and is accommodated in various kinds of electronic apparatuses. A number of such apparatuses accommodates different kinds of crystal units in response to the uses. For example, in small mobile electronic apparatuses including recent portable telephones, a thickness-shear mode crystal unit of AT cut, which generates communication frequency signals, and a tuning fork type crystal unit, which generates clock signals are separately accommodated. The separate accommodation of a plurality of crystal units inhibits the electronic apparatuses from being downsized, and accordingly for example, in Japanese Laid-open Patent Application No. 2000-349181 (JP 2000-349181A), there has been proposed that both of different kinds of crystal blanks are encapsulated in a common container or vessel for the miniaturization purpose.
An example of the conventional multifunctional crystal unit accommodating therein a plurality of crystal blanks of such different vibration modes is illustrated in
FIGS. 1 and 2
.
As illustrated in
FIG. 1
, the crystal unit houses two kinds of crystal blanks
2
and
3
in substantially rectangular parallelepiped container
1
for surface mounting. Container
1
is constructed of laminated ceramics to have a recess formed from its upper face, and as illustrated in
FIG. 2
, container
1
is formed, at four corners of its outer bottom face, with mounting electrodes
4
a
,
4
b
,
5
a
and
5
b
used for connection with external circuits. Mounting electrodes
4
a
,
4
b
,
5
a
and
5
b
are formed so as to be somewhat extended and to rise up on the side faces of container
1
. In the recess of container
1
, stepped portions are formed. On the upper face of container
1
along the periphery of the recess, for example, metallic ring
6
is mounted to which metallic cover
7
is bonded by seam welding, and hereby crystal blanks
2
and
3
are hermetically encapsulated in container
1
.
As illustrated in
FIG. 3A
, crystal blank
2
is a tuning fork type crystal blank which is made of quartz crystal plate of X cut and has vibration mode of length-width-flexure mode, and consists of a fork base portion
8
and a pair of fork arms
9
a
and
9
b
. Respective fork arms
9
a
and
9
b
of a columnar shape have four faces in which electrically paired excitation electrodes
10
are provided. Further, on both end portions of fork base portion
8
are provided extending electrodes
11
a
and
11
b
, so that respective excitation electrodes are extended to extending electrodes
11
a
and
11
b
. Extending electrodes
11
a
and
11
b
are fixedly bonded by conductive adhesive
12
to a pair of terminal electrodes (not illustrated) formed in the bottom face of the recess of container
1
so as to provide therebetween electrical and mechanical connection. Thus, tuning fork type crystal blank
2
is held within the recess of container
1
, so that the plate face thereof is directed vertically. The pair of terminal electrodes to which tuning fork type crystal blank
2
is connected, are electrically connected to the above-described mounting electrodes
5
a
and
5
b
through conductive patterns and via-holes formed in the inner face of container
1
.
On the other hand, crystal blank
3
of AT cut is a planar plate like crystal blank acquired by being cut out of a quartz crystal by means of AT cut, and has both principal planes in which paired excitation electrodes
13
are formed. Further, crystal blank
3
formed in a rectangular shape has one side formed, at its opposite ends, with a pair of extending electrodes
14
a
and
14
b
to which the pair of excitation electrodes
13
are extended, respectively.
In the stepped portion of the recess of container
1
are formed a pair of terminal electrodes (not illustrated) to which extending electrodes
14
a
and
14
b
are fixedly bonded by means of conductive adhesive
12
to establish electrical and mechanical connection between the electrodes. Thus, crystal blank
3
of AT cut is held within the recess of container
1
in a manner such that the plate face is directed in a vertical direction. Crystal blank
3
of AT cut is disposed above tuning fork type crystal blank
2
. The pair of terminal electrodes to which crystal blank
3
of AT cut is connected are electrically connected to the above-described mounting electrodes
4
a
and
4
b
, respectively, through conductive patterns and via-holes formed in the inner face of container
1
.
In the described multifunctional crystal unit, tuning fork type crystal blank
2
vibrates at dozen kiloheltz to generate a reference frequency signal for clock use, while crystal blank
3
of AT cut vibrates at several through dozen megaheltz for generating communication frequency in a communication apparatus. For example, when this crystal unit is employed for a cellular telephone, the crystal unit is mounted on a printed wiring board of the cellular telephone, so that mounting electrodes
5
a
and
5
b
are connected to an oscillating circuit for clock signal, and mounting electrodes
4
a
and
4
b
are connected to an oscillating circuit for communication frequency use. Thus, tuning fork type crystal blank
2
is used as a crystal unit operating at a kilohertz band, while crystal blank
3
of AT cut is used as a crystal unit operating at a megaheltz band.
As described above, when different kinds of crystal blanks are housed in the same container for the surface mount use to be used as two kinds of crystal units, the size of the whole crystal unit can be kept small. Therefore, when this type of multifunctional crystal unit is employed, it is possible to miniaturize electronic apparatuses such as cellular telephones.
In the multifunctional crystal unit of the above-described constitution, when tuning fork type crystal blank
2
and crystal blank
3
of AT cut are respectively mounted to be held in the recess bottom and the stepped portion of container
1
, the respective vibration frequencies must be adjusted. Namely, after when conductive adhesive
12
is thermally hardened to fixedly bond tuning fork type crystal blank
2
to the bottom portion of the recess, either the tip ends of fork arms
9
a
and
9
b
are cut off, for example, by machining, or metallic films provided at the tip ends of tuning fork arms
9
a
and
9
b
are removed away by, for example, laser processing, to adjust the vibration frequency. Then, after the adjustment of tuning fork type crystal blank
2
, crystal blank
3
of AT cut is held at the stepped portion by means of conductive adhesive
12
, and for example, ion beam is radiated to excitation electrodes
13
of crystal blank
3
so as to reduce film thickness of excitation electrodes
13
thereby adjusting the vibration frequency thereof. After the completion of the adjustment of the vibration frequencies, the common metallic cover
7
is attached so as to close the recess, and the manufacture of the crystal unit is completed.
In the described crystal unit, during the adjustment of the vibration frequency of crystal blank
3
of AT cut, metallic dusts scatting from excitation electrodes
13
might attach to tuning fork type crystal blank
2
to cause a problem such as, for example, a change in the vibration frequency and the short-circuiting between excitation electrodes
10
of tuning fork type crystal blank
2
, resulting in an occurrence of defective. Although it might be possible to adopt an alternate way such that the crystal blank of AT
Katten Muchin Zavis & Rosenman
Nihon Dempa Kogyo Co. Ltd
Oliva Carmelo
Reichard Dean A.
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