Active solid-state devices (e.g. – transistors – solid-state diode – Field effect device – Responsive to non-optical – non-electrical signal
Reexamination Certificate
2001-04-25
2003-01-28
Elms, Richard (Department: 2824)
Active solid-state devices (e.g., transistors, solid-state diode
Field effect device
Responsive to non-optical, non-electrical signal
C438S051000, C438S053000
Reexamination Certificate
active
06512255
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a semiconductor pressure sensor device having a sensor chip mounted on a resin package and covered with a protective member, for detecting a pressure and producing an electrical signal in accordance with the detected pressure, which is suitably used for detecting an engine intake pressure of an vehicle.
2. Description of the Related Art
A conventional semiconductor pressure sensor device for detecting a negative pressure such as an engine intake pressure of a vehicle or the like is constructed as shown in
FIGS. 10A and 10B
. The sensor device has a semiconductor sensor chip
102
as a pressure-detecting element. The sensor chip
102
has a diaphragm
102
a
made of a material (for instance, single crystal silicon) utilizing a piezoresistance effect, and several diffusion resistances (not shown) formed on the diaphragm
102
a
and connected to form a bridge circuit. Changes in value of resistances of the diffusion resistances caused by the deformation of the diaphragm
102
a
are taken out of the bridge circuit as electrical signals.
The sensor chip
102
is mounted on a recess portion (sensor mount portion)
103
formed in a resin package
101
through a glass base
105
by adhesive or the like. The sensor chip
102
is electrically connected to conductive members
104
, which are insert-molded with the resin package
101
, by bonding wires
106
. Accordingly, this sensor device can output an electrical signal corresponding to the negative pressure applied thereto.
The sensor chip
102
and the bonding wires
106
are covered with protective members J
1
, J
2
made of insulating materials for protection, electrical insulation, and anticorrosion. In view of a method for forming the protective members in the recess portion
103
, there are two kinds of structures, a partially filling structure and a fully filling structure.
FIG. 10A
shows the partially filling structure. In this structure, after the sensor chip
102
, the bonding wires
106
, and the entire surface of the recess portion
103
are covered with a thin film resin J
1
made of an organic material, the surface of the diaphragm
102
a
of the sensor chip
102
, connection portions between the chip
102
and the wires
106
, and connection portions between the wires
106
and the conducive members
104
are covered with a soft protective resin J
2
. The protective resin J
2
is generally a soft gel-like insulating material such as fluorine-containing gel that can be formed by coating and thermal setting. The thin film resin J
1
is, for instance, a palylene (polychloroparaxylylene) film that can be formed by a CVD (Chemical Vapor Deposition) method, which has good adhesion to the protective resin J
2
.
On the other hand,
FIG. 10B
shows the fully filling structure in which a protective resin J
2
fills the recess portion
103
to cover the sensor chip
102
and the bonding wires
106
. According to this fully filling structure, the sensor chip
102
and the bonding wires
106
can be easily covered with soft resin such as gel without forming an organic resin thin film that has a high elastic modulus and necessitates an expensive vacuum deposition apparatus. Therefore, in the fully filling structure, since the protective member produces lower stress than that in the partially filling structure, reliability is improved. In addition, since there is no need to use the vacuum deposition apparatus, manufacturing cost is reduced.
The fully filling structure, however, has a problem that bubbles are liable to be produced in the protective resin J
2
due to moisture and substances such as gasoline and exhausted condensed gas contained in environment when the sensor device detects the engine intake pressure of the vehicle. That is, such substances are dissolved into the protective resin J
2
, and evaporated by heat and pressure to produce bubbles in the resin J
2
.
The occurrence of bubbles is explained in more detail with reference to
FIGS. 11A and 11B
. In the fully filling structure, the thickness of the protective resin J
2
is thicker than that in the partially filling structure, and, for instance, is more than 1 mm. Because of this, gases produced by substances dissolved in the protective resin J
2
are difficult to be released from the protective resin J
2
. As a result, the substances and moisture caught inside the protective resin J
2
are vaporized when temperature rises, and, as shown in
FIG. 11A
, remain in the protective film J
2
as bubbles K
1
. The bubbles K
2
grow when the temperature further rises or pressure is negative.
As shown in
FIG. 11B
, the grown bubbles K
1
can produce cracks K
2
that extends from the inside to the surface of the protective resin J
2
. The cracks K
2
may generate leakage current from the sensor chip
102
or the bonding wires
106
(in the figure, from the bonding wires
106
). The bubbles K
1
existing in the vicinity of the connection portion of one the wires
106
with the sensor chip
102
or with the conductive member
104
(with the conductive member
104
in the figure) may cause breakage of the wire
106
.
SUMMARY OF THE INVENTION
The present invention has been made in view of the above problems. An object of the present invention is to prevent bubbles from being produced in a protective member covering a sensor chip and an electrically connecting portion of the sensor chip in a semiconductor pressure sensor device.
According to the present invention, a protective member for covering a sensing portion of a sensor chip and a bonding wire has a saturated swelling coefficient of approximately 7 wt % at most when the protective member is immersed into gasoline having a temperature of 20° C. The protective member can prevent bubble from being produced therein. No leakage current and no breakage of the wire occur by bubbles.
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patent: 5914507 (1999-06-01), Polla et al.
patent: 6260417 (2001-07-01), Watanabe et al.
patent: 2002/0062698 (2002-05-01), Baba et al.
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patent: 1-140037 (1989-06-01), None
patent: 9-43084 (1997-02-01), None
Aoki Takashi
Nomura Takashi
Watanabe Yoshifumi
Denso Corporation
Law Offices of David G. Posz
Wilson Christian D.
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