Measuring and testing – Fluid pressure gauge – Electrical
Reexamination Certificate
1999-10-13
2001-07-17
Oen, William (Department: 2855)
Measuring and testing
Fluid pressure gauge
Electrical
Reexamination Certificate
active
06260417
ABSTRACT:
CROSS REFERENCE TO RELATED APPLICATION
This application is based upon Japanese Patent Application No. 10-115211, filed on Apr. 24, 1998.
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a semiconductor pressure sensor device including a semiconductor pressure sensor chip mounted on a resin package for detecting a negative pressure.
2. Description of the Related Art
Generally, a semiconductor pressure sensor chip utilizing a piezoresistance effect is adopted as a pressure detecting element to a pressure sensor device for detecting an intake pressure of an automotive engine. This kind of pressure sensor chip includes several diffusion resistors. The diffusion resistors are disposed on a diaphragm made of a material (for instance, single crystal silicon) capable of providing the piezoresistance effect, and are connected into a bridge circuit. A pressure signal is taken out from the bridge circuit in accordance with changes in resistance values of the diffusion resistors which are caused by displacement of the diaphragm.
The pressure sensor chip is conventionally mounted on a resin package. For instance, the sensor chip is disposed on a sensor mount part of the resin package through adhesive by die bonding, and is electrically connected to a conductive part through conductive wires. The conductive part is formed at the resin package side by insert-molding. The pressure sensor chip and the bonding wires are covered with a protective member made of an insulating material to protect them from corrosion, and to secure those insulating performance. In this case, a gel-like insulating material is generally used as the protective member not to inhibit the displacement of the diaphragm.
The covering step by the protective member is carried out under a vacuum atmosphere to prevent voids from being produced in the protective member and within a region covered by the protective member. However, it is very difficult to completely remove air existing in a gap produced between the resin package and the conductive part formed by insert-molding. In addition, the surface of the conductive part is usually plated with gold having low affinity. This results in low adhesiveness between the gel-like protective member and the surface of the conductive part, thereby allowing a state where air is trapped at the interface part.
Because of this, when the semiconductor pressure sensor device detects a negative pressure such as an engine intake pressure, voids produced by air described above within the gel-like protective member grow. The grown voids may move within the gel-like protective member to cause deterioration of the insulating performance and breakage of the wire bonding.
When the semiconductor pressure sensor chip is mounted on a ceramic package by utilizing a wire-bonding technique as disclosed in U.S. Pat. No. 5,357,673, generation of voids can be suppressed as compared to the case adopting the resin package case described above. However, the ceramic package also necessitates bonding pad parts, and therefore, it is difficult to prevent voids from being produced at the interface between the bonding pad parts and the protective member. In addition, since the ceramic package is composed of several members, a number of parts is increased.
SUMMARY OF THE INVENTION
The present invention has been made in view of the above problems. An object of the present invention is to provide a semiconductor pressure sensor device for detecting a negative pressure with improved operational reliability by preventing voids from being produced within a protective member covering a semiconductor pressure sensor.
According to the present invention, a semiconductor pressure sensor device has a sensor chip mounted on a resin package and electrically connected to a conductive part on the resin package, a first protective member covering a portion including an entire surface of the conductive part and excluding a sensing part of the sensor chip, and a second protective member covering the first protective member and the sensing part. The first protective member has a Young's modulus larger than that of the second protective member.
Accordingly, even when air is trapped in a gap produced between the resin package and the conductive part and at an interface between the first protective member and the conductive part, since the first protective member having a relatively large Young's modulus covers the conductive part, voids are prevented from being produced by air described above. Further, since the sensing part of the sensor chip is covered with the second protective member having a relatively small Young's modulus, a preferable insulating performance can be provided without deteriorating the sensing performance of the sensor chip.
REFERENCES:
patent: 4732042 (1988-03-01), Adams
patent: 5357673 (1994-10-01), Polak
patent: 5877425 (1999-03-01), Suzuki et al.
patent: 5-145085 (1993-06-01), None
patent: 10-170381 (1998-06-01), None
patent: 11-241970 (1999-09-01), None
patent: 11-304619 (1999-11-01), None
Aoki Takashi
Okada Hiroyuki
Watanabe Yoshifumi
Denso Corporation
Oen William
Pillsbury & Winthrop LLP
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