Measuring and testing – Fluid pressure gauge – With protective separator
Reexamination Certificate
2000-08-01
2002-04-23
Oen, William (Department: 2855)
Measuring and testing
Fluid pressure gauge
With protective separator
Reexamination Certificate
active
06374678
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a pressure sensor and a method of manufacturing the same and, more particularly, to a pressure sensor using a piezoelectric or capacitive semiconductor sensor chip and a method of manufacturing the same.
In conventional packaging of a pressure sensor of this type, a sensor chip made of a semiconductor is generally mounted on a metal base (to be referred to as a metal stem hereinafter). In this case, a glass buffer member is conventionally formed between the metal stem and sensor chip in order to prevent the sensor chip from being broken by a stress generated during heating due to a difference in coefficient of thermal expansion between the metal stem and sensor chip.
Electrode pins for outputting electrical signals are fixed in a plurality of through holes formed in the metal stem around the sensor chip with low-melting glass to be hermetically sealed and insulated. The electrodes of the sensor chip and the electrode pins are connected to each other through bonding wires.
A conventional pressure sensor shown in
FIG. 12
is constituted by a sensor chip
101
, bonding wires
102
, electrode pins
103
, a buffer member
104
, hermetic seal glass members
105
, a metal stem
106
, a metal container
110
, and a barrier diaphragm
111
. The metal container
110
and barrier diaphragm
111
are indicated by alternate long and two short dashed lines to show the internal structure of the pressure sensor.
The sensor chip
101
is a piezoelectric or capacitive pressure sensor chip made of a semiconductor such as silicon. The bonding wires
102
electrically connect the electrode pads (not shown) of the sensor chip
101
and the electrode pins
103
to each other. The electrode pins
103
are made of a conductive metal and are fixed in through holes
106
a
(
FIG. 13
) formed in the metal stem
106
to extend through them.
The buffer member
104
formed on the metal stem
106
is made of a glass material to prevent the sensor chip
101
from being broken by a difference in coefficient of thermal expansion between the sensor chip
101
and metal stem
106
. The hermetic seal glass members
105
are made of a low-melting glass, and realize hermetic seal in the gaps between the inner surfaces of the through holes
106
a
and the electrode pins
103
.
The metal stem
106
has a disk-like shape, and five through holes
106
a
are formed in it to correspond to the electrode pins
103
. The metal container
110
has a cylindrical shape to cover the whole sensor chip
101
mounted on the metal stem
106
. The interior of the metal container
110
is filled with sealed oil such as silicone oil. The barrier diaphragm
111
is comprised of a flexible metal film and deforms in accordance with an external pressure to transmit it to the sensor chip
101
through the silicone oil. When the external pressure disappears, the barrier diaphragm
111
is restored to the initial position.
As shown in
FIG. 13
, the buffer member
104
is formed at the central portion of the metal stem
106
, and the sensor chip
101
is placed on the buffer member
104
. The sensor chip
101
and electrode pins
103
are connected to each other through the bonding wires
102
.
The through holes
106
a
formed in the metal stem
106
have diameters slightly larger than the diameters of the electrode pins
103
. The hermetic seal glass members
105
are interposed in the gaps between the electrode pins
103
and the inner surfaces of the through holes
106
a
. The hermetic seal glass members
105
are softened once by heating, and then cooled to solidify. The gaps between the metal stem
106
and electrode pins
103
are completely hermetically sealed. Therefore, the silicone oil filled in the metal container
110
will not leak to the lower side of the metal stem
106
through the through holes
106
a.
A method of manufacturing the conventional pressure sensor described above will be described with reference to FIG.
14
. As shown in
FIG. 14
, the electrode pins
103
are inserted in holes
105
a
of the cylindrical hermetic seal glass members
105
. The hermetic seal glass members
105
with the inserted electrode pins
103
are inserted in the through holes
106
a
of the metal stem
106
, and the metal stem
106
is placed on a jig
107
having holes
107
a
. The holes
107
a
have diameters substantially equal to the diameters of the electrode pins
103
. The electrode pins
103
projecting from the hermetic seal glass members
105
are inserted in the holes
107
a.
In this manner, the metal stem
106
that supports the electrode pins
103
is placed on the jig
107
, and the metal stem
106
is heated until the hermetic seal glass members
105
are softened. The metal stem
106
is then cooled to solidify the softened hermetic seal glass members
105
, thereby hermetically sealing the gaps between the electrode pins
103
and through holes
106
a
completely. A base unit
112
is thus completed.
Meanwhile, a wafer comprised of sensor chips and a glass plate are connected to each other by anodic bonding, and the resultant structure is diced, thereby forming a plurality of sensor chips
101
with buffer members
104
bonded to their lower surfaces. The sensor chip
101
is then adhered onto the base unit
112
through the buffer member
104
, and electrode pads (not shown) on the sensor chip
101
and the electrode pins
103
are connected to each other through the bonding wires
102
. The whole sensor chip
101
is covered by the metal container
110
and barrier diaphragm
111
, and silicone oil is injected into the metal container
110
, thus completing a pressure sensor.
FIG. 15
shows a state wherein the electrode pins
103
are positioned by the jig
107
. As shown in
FIG. 15
, since the diameters of the holes
107
a
of the jig
107
are substantially equal to the diameters of the electrode pins
103
, the electrode pins
103
are positioned at the centers of the corresponding through holes
106
a
by the jig
107
. Even when the hermetic seal glass members
105
are softened by heating, the positions of the electrode pins
103
will not shift.
The conventional pressure sensor described above has the following problems.
As described above, to fabricate a pressure sensor structure shown in
FIG. 12
, at least three bonding steps are required, i.e., the first step of hermetically sealing the metal stem and electrode pins with glass, the second step of bonding (bonding a wafer before dicing) the sensor chip and glass buffer member by anodic bonding, and the third step of adhering the glass buffer member and metal stem.
Too many steps are necessary in this manner, leading to a possible decrease in quality and increase in cost.
When a diaphragm structure using the barrier diaphragm
111
and the sealed oil is employed, since the amount of sealed oil is large, the temperature characteristics of the pressure sensor degrade. For this reason, conventionally, a structure made of glass, a ceramic material, a resin, or the like is formed around the buffer member
104
to decrease the amount of sealed oil. This, however, increases the number of steps and the number of components in turn.
In adhesion of the buffer member
104
and metal stem
106
, glass sealing, and die bonding such as fixing, stress-free bonding cannot be achieved unless not only the coefficients of thermal expansion of the buffer member
104
and metal stem
106
are matched but also the coefficient of thermal expansion of the adhesive that adheres the buffer member
104
and metal stem
106
is also matched with those of the buffer member
104
and metal stem
106
. In order to avoid this stress, conventionally, the thickness of the buffer member
104
is increased, so that the amount of stress propagating to the sensor chip
101
is attenuated. As the size of the buffer member
104
increases, however, the amount of sealed oil increases, and dicing of the buffer member
104
becomes difficult, which are new problems.
Although the metal stem
106
and electrode pins
103
preferably abut again
Blakely & Sokoloff, Taylor & Zafman
Oen William
Yamatake Corporation
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