Oscillators – Electromechanical resonator – Crystal
Reexamination Certificate
2002-09-25
2004-04-13
Pascal, Robert (Department: 2817)
Oscillators
Electromechanical resonator
Crystal
C331S068000
Reexamination Certificate
active
06720837
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a quartz crystal oscillator of a surface-mount type, and more particularly, to a quartz crystal oscillator which prevents fluctuations in frequency when an impact is applied thereto.
2. Description of the Related Art
A surface mounting crystal oscillator is used mainly as a frequency reference source particularly for a variety of portable electronic devices such as portable telephones because of its compact size and light weight. In recent years, an increasingly strict tolerance is imposed for a frequency deviation of an oscillation frequency in a surface mounting crystal oscillator. For example, a crystal oscillator for a portable telephone is required to limit a frequency variation ratio with respect to a reference frequency (nominal frequency), for example, within ±1 ppm.
FIG. 1
is a cross-sectional view illustrating an exemplary configuration of a conventional surface mounting crystal oscillator. As disclosed, for example, in Japanese Patent No. 2969526 (JP, 2969526, B), the illustrated crystal oscillator comprises IC (integrated circuit) chip
2
and quartz crystal blank
3
contained in container body
1
, and metal cover
4
overlaid to hermetically encapsulate these components. Container body
1
, which is made of laminated ceramics, is formed with a recess on its top surface, and the recess has steps on its inner wall. On the bottom and side surfaces of container body
1
, which define outer surfaces thereof, mounting electrodes
5
are formed each for surface mounting. Mounting electrodes
5
are used to connect the crystal oscillator to an external circuit which is provided on a printed wiring board when the crystal oscillator is mounted on the printed wiring board.
IC chip
2
has an oscillator circuit integrated therein, which utilizes a quartz crystal unit comprised of crystal blank
3
.
FIG. 2
illustrates the circuit arrangement of the crystal oscillator. Oscillation capacitors Ca, Cb are connected respectively to one and the other ends of crystal unit
3
A comprised of crystal blank
3
for making up a resonance circuit. These capacitors Ca, Cb have their other ends connected to a ground potential. An input and an output terminal of oscillation amplifier
6
are connected respectively to one and the other ends of crystal unit
3
A for amplifying and feeding back an oscillation frequency which depends on the resonance circuit. Feedback resistor
7
is also connected between the input and output terminals of oscillation amplifier
6
. Within the circuit indicated by solid lines in
FIG. 2
, portions except for crystal unit
3
A are formed in IC chip
2
.
Although not shown in
FIG. 2
, a pair of connection terminals for use in connection with crystal unit
3
A, a power supply terminal, an output terminal, and a ground terminal are provided on one major surface of IC chip
2
. Corresponding to these terminals, a circuit pattern is formed on the bottom of the recess in container body
1
. Then, the one major surface of IC chip
2
, on which the respective terminals are exposed, is secured on the bottom of the recess in container body
1
by facedown bonding. The facedown bonding involves, for example, providing a gold (Au) bump on each of the terminals exposed on the one major surface of IC chip
2
, and bonding the gold bumps with the circuit pattern on container body
1
by ultrasonic thermocompression bonding. Container body
1
is provided with via-holes and the like for electrically connecting the circuit pattern on the bottom of the recess with mounting electrodes
5
, such that the power supply terminal, output terminal, and ground terminal of IC chip
2
are electrically connected to mounting electrodes
5
by the facedown bonding.
Crystal blank
3
is, for example, an AT-cut quartz crystal blank, and is provided with a pair of excitation electrodes (not shown) on both major surfaces, and extending electrodes are extended from these excitation electrodes toward both ends of one side of crystal blank
3
. Then, crystal blank
3
is held within the recess by securing leading ends of both extending electrodes to the steps formed on the inner wall of container body
1
with conductive adhesive
8
. In this event, the other end of crystal blank
3
is carried on the step in contact with or in close proximity to the same. A pair of extending electrodes of crystal blank
3
are connected to the pair of connection terminals of IC chip
2
through the circuit pattern formed within the recess of container body
1
. Metal cover
4
is bonded to metal ring
9
disposed on the top surface of a side wall of container body
1
by seam welding to seal the opening face of the recess.
In the crystal oscillator configured as described above, IC chip
2
and crystal blank
3
are accommodated in a single recess of container body
1
, so that the crystal oscillator can be reduced particularly in height, as compared with a crystal oscillator which has recesses in both major surfaces of a container such that a crystal blank is hermetically accommodated in the recess in one major surface while an IC chip is accommodated in the recess in the other major surface. When the container body is formed with recesses on both major surfaces, the resulting container body has an H-shaped cross-section. Since the container body is required to withstand a force applied thereto when the IC chip is secured by compression bonding, the strength of the container body must be enhanced by increasing the thickness of a horizontal part in the H-shaped cross-section, resulting in a correspondingly increased height of the container body.
However, the conventional surface mounting crystal oscillator as illustrated in
FIG. 1
has a problem that the frequency fluctuates when a drop impact is applied to the crystal oscillator. Specifically, when a finished crystal oscillator is applied with an impact in a drop impact test by dropping the same to a concrete floor from 1.5 meters above, the oscillation frequency fluctuates in the positive direction, resulting in a failure in satisfying a regulation against the oscillation frequency which stipulates, for example, that a deviation &Dgr;f/f shall be within 1 ppm, where f is a nominal oscillation frequency, and &Dgr;f is a frequency changing amount from the nominal oscillation frequency.
The drop impact test herein referred to involves dropping a surface mounting crystal oscillator twice in positive and negative directions, respectively, with respect to three-dimensional coordinate axis directions (X-, Y-, Z-directions) in one cycle as defined herein, and recording a frequency change (&Dgr;f/f) in each cycle. Here, the test is conducted in ten cycles.
FIG. 3
shows the result of the drop impact test conducted for a conventional surface mounting crystal oscillator, the oscillation frequency (nominal frequency) f of which is 14.4 MHz. Ten crystal oscillators were tested, and
FIG. 3
shows frequency changes in each cycle for the one which presented the largest frequency change and the one which presented the smallest frequency change, respectively.
SUMMARY OF THE INVENTION
It is therefore an object of the present invention to provide a surface mounting quartz crystal oscillator which maintains a small height, reduces a frequency change caused by an impact, and has a small frequency deviation and a small frequency changing amount.
The present inventors diligently made investigations on fluctuations in frequency caused by a drop impact as described below to complete the present invention. Specifically, the object of the present invention is achieved by a surface mounting crystal oscillator which includes a container body having a recess, a crystal blank having one end held on a step formed on an inner wall of the recess and functioning as a crystal unit vibrator, an IC chip secured on the bottom of the recess, and a metal cover for sealing an opening face of the recess. The IC chip has integrated therein a first and a second capacitor connected to one and the other ends
Kubo Kuichi
Moriya Kouichi
Narita Yoshinori
Sato Katsuyuki
Chang Joseph
Katten Muchin Zavis & Rosenman
Nihon Dempa Kogyo Co. Ltd
Pascal Robert
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