Oscillators – With outer casing or housing
Reexamination Certificate
2000-08-30
2002-09-03
Kinkead, Arnold (Department: 2817)
Oscillators
With outer casing or housing
C331S10800D, C331S158000, C257S701000, C438S112000, C310S348000, C310S352000, C310S353000
Reexamination Certificate
active
06445254
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a crystal oscillator in which a crystal blank and an IC (integrated circuit) chip are accommodated in a vessel and a method of fabricating the same. In more particularly, the present invention relates to a crystal oscillator and a method of fabricating the same in which the IC chip is fixed through a bump to the vessel by means of ultrasonic thermocompression bonding.
2. Description of the Related Art
A crystal oscillator is widely utilized as a device for providing a reference frequency and a reference time in various electronic apparatus including communication equipment. Recently, as is represented by portable equipment such as a portable telephone, the size of the apparatus becomes smaller and smaller. Thus, the crystal oscillator is also requested to be made small. The size requested for the crystal oscillator is, for example, 3 mm×5 mm for the bottom face thereof and 1 mm for the height itself. For this reason, when an IC chip including the crystal oscillator is mounted on a vessel or the like, the manner of mounting is changed from a conventional wire bonding to a face down bonding (FDB) in which one major surface of the IC chip having terminal electrodes formed thereon is brought into the vessel with its face down and bonded to an opposing substrate. As an example of the face down bonding, there has been proposed a bonding method using ultrasonic thermocompression bonding employing a bump.
FIG. 1
is a diagram showing a cross-sectional view of a general arrangement of a crystal oscillator.
FIG. 2
is an oblique view showing an outer appearance of the crystal oscillator shown in
FIG. 1
, and
FIG. 3
is a diagram showing a bottom view of the crystal oscillator shown in FIG.
1
.
As shown in
FIG. 1.
, the crystal oscillator includes vessel main body
1
, IC chip
2
and crystal blank
3
accommodated in vessel main body
1
, and cover
4
bonded on vessel main body
1
. Vessel main body
1
is formed of bottom wall
5
, intermediate frame wall
6
and upper frame wall
7
, and thus concave portion
1
a
and step portion are formed in vessel main body
1
. The components constituting vessel main body
1
is made of baked ceramic of a multilayer structure. IC chip
2
has a number of electronic components integrated thereon such as an amplifier and so on constituting an oscillation circuit. On one major surface of IC chip
2
, there are provided crystal terminals
8
a
and
8
b
utilized when it is connected to crystal blank
3
. IC chip
2
is fixed to the bottom surface of concave portion
1
a
of vessel main body
1
at the one major surface through, for example, bumps
9
by means of ultrasonic thermocompression bonding, in a manner of face down bonding.
As shown in
FIG. 4
, crystal blank
3
has a substantial rectangular shape and has a pair of excitation electrodes
14
a
and
14
b
on both of the major surfaces opposing to each other, respectively. Each of the excitation electrodes
14
a
and
14
b
has leading electrode
15
a
,
15
b
extended toward the ends opposing to each other in the longitudinal direction of the crystal blank. Crystal blank
3
is fixed to the step portion at both the ends thereof by using conductive adhesive
10
. Thus, crystal blank
3
is electrically and mechanically connected to a crystal connection terminal formed at the step portion. Cover
4
is bonded on vessel main body
1
by means of seam welding metal ring
11
.
Pair of leading electrodes
15
a
and
15
b
of crystal blank
3
extend through a through-hole provided at the step portion of vessel main body
1
and connected to crystal terminals
8
a
and
8
b
of IC chip
2
. Each of the terminals of power supply, signal output, ground or the like of IC chip
2
is led to the bottom surface or side surface of vessel main body as outer electrode
12
. Further, in order to measure electric characteristic of the crystal oscillator and electric characteristic of crystal blank
3
as a unit component, the pair of leading electrodes
15
a
and
15
b
of crystal blank
3
are extended to the side surfaces of vessel main body
1
to form measuring terminals
13
a
and
13
b
on the side surfaces. In
FIG. 1
, a portion denoted by a black bold line represents a conductive portion for establishing electric connection such as a through-hole, a conductive path which will be described later on, an electrode, an intetlayer connection or the like.
When the device as a product is shipped, the crystal oscillator contained in the device is subjected to a forcible excitation washing. The forcible excitation washing is carried out as a countermeasure for so-called DLD (Drive Level Dependency) in which crystal oscillator
3
becomes unresponsive in oscillation to a small level of excitation. However, in the arrangement of the above crystal oscillator shown in
FIG. 5
, measuring terminals
13
a
and
13
b
of crystal oscillator
3
are also electrically connected to crystal terminals
8
a
and
8
b
of IC chip
2
, respectively. For this reason, if a voltage high enough to effect the forcible excitation washing is applied to crystal blank
3
through measuring terminals
13
a
and
13
b
, then IC chip
2
can also be applied with the voltage excessively through crystal terminals
8
a
and
8
b
, which fact can cause electrical damage on IC chip
2
.
General manner of bonding IC chip
2
to a vessel or the like to form a crystal oscillator will hereinafter be described.
As shown in
FIG. 6
, a plurality of conductive paths
25
as a circuit pattern are formed on a bottom surface, or bottom wall
5
of concave portion
1
a
of vessel main body
1
. A base layer of conductive paths
25
is made of tungsten (W) by printing and burning as a base electrode. Thereafter, a gold (Au) layer is provided on the surface of the base layer by electrolytic plating. In an ordinary manner, conductive path
25
is covered with an insulating material such as alumina or the like (not shown) except for connection terminal portion
26
, which serves as an end contact area of conductive path
25
, denoted by applying A half-tone notation in FIG.
6
. Connection terminal portion
26
is formed into a rectangular shape extending in the longitudinal direction of conductive path
25
.
On the other hand, IC chip
2
is supplied as a bare chip or a flip chip. As shown in
FIG. 7
, IC chip
2
is formed into a rectangular shape having a plurality of terminal electrodes
27
formed along a pair of side edges opposing to each other on one major surface of the chip. Each of terminal electrodes
27
has provided thereon ball-like bump
28
made of a gold grain, for example. When IC chip
2
is mounted in concave portion
1
a
of vessel main body
1
, IC chip
2
is brought into concave portion
1
a
so that one major surface of the IC chip on which the bumps are provided is opposing relationship with the bottom surface of concave portion
1
a
and bumps
29
and connection terminal portions
26
are aligned with and bonded to each other. Then, IC chip
2
is pressed and ultrasonic wave is supplied to IC chip
2
by an ultrasonic thermocompression bonding machine so that IC chip
2
is vibrated in the horizontal direction. Thus, bump
28
is crashed and formed into an elliptical shape and electrical connection is established between terminal electrode
27
and connection terminal portion
26
through bump
28
. Bonding is achieved by effecting solid phase diffusion in the metal (in this case, gold).
Since crystal blank
3
has a rectangular shape elongated in one direction, the bottom surface of concave portion
1
a
of vessel main body
1
also becomes elongated rectangular shape. Therefore, if small-sizing of the crystal oscillator is developed, almost no allowance is provided between the side wall of the concave portion and IC chip
2
in the width direction. For this reason, conductive path
5
tends to be provided on both the sides in the longitudinal direction in which certain allowance can be expected. Thus, IC chip
2
is arranged to
Gong Xinglong
Negishi Susumu
Oda Seiji
Sakaba Yasuo
Shibuya Tatsunobu
Kinkead Arnold
Nihon Dempa Kogyo Co. Ltd.
Oblon & Spivak, McClelland, Maier & Neustadt P.C.
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