Measuring and testing – Fluid pressure gauge – Electrical
Reexamination Certificate
2002-03-07
2003-07-22
Noori, Max (Department: 2855)
Measuring and testing
Fluid pressure gauge
Electrical
C073S862680, C073S715000
Reexamination Certificate
active
06595067
ABSTRACT:
CROSS REFERENCE TO RELATED APPLICATION
This application is based on and incorporates herein by reference Japanese Patent Application No. 2001-113079 filed on Apr. 11, 2001.
FIELD OF THE INVENTION
This invention relates to a pressure sensor for outputting a signal corresponding to an applied pressure by means of a piezo-resistance effect, made by bonding a sensor element to a metal stem.
BACKGROUND OF THE INVENTION
Pressure sensors of this kind have been proposed which, to detect high pressures, are made by bonding a sensor element (sensor chip) made from a semiconductor to a metal stem with a low melting point glass, as disclosed in U.S. Pat. No. 4,840,067.
However, in this pressure sensor, because a low melting point glass is used to bond the sensor chip to the metal stem, heating to a temperature (for example about 480° C.) is necessary. Therefore, this bonding is not suitable for sensor chips which are vulnerable to heat (for example chips with integrated circuit parts).
Resin adhesives are considered to be used for bonding sensor elements to metal stems, as a bonding method which can be implemented at relatively low temperatures. However, when low melting point glass is simply replaced with a resin adhesive, as a result of creep progressing in the adhesive resin with temperature changes, stresses act on the sensor chip, and the output of the sensor fluctuates with time.
SUMMARY OF THE INVENTION
It is therefore an object of the present invention to reduce fluctuations in sensor output caused by temperature changes in a pressure sensor made by bonding a sensor element to a metal stem with a resin adhesive.
The present invention is based on a supposition that, if the progressing of creep which accompanies temperature changes in the resin adhesive were to be slowed, then fluctuation of the sensor output could be reduced. It is known that, in a resin, the relationship between the creep rate CR and the stress &sgr; acting on the resin is given by the following expression.
CR=A×&sgr;
B
(where A and B are constants)
According to the present invention, a pressure sensor has a sensor element operable based on the piezo-resistance effect and a metal stem bonded to this sensor element and supporting the sensor element. The sensor element and the metal stem are bonded with a resin adhesive. This resin adhesive has a creep characteristic such that the constant B in the above expression is not greater than 3.5, preferably to be less than 3.0. Thus, sensor output fluctuation could be reduced to a practically tolerable level. Further preferably, the resin adhesive may be made of an imide resin.
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patent: 5583295 (1996-12-01), Nagase et al.
patent: 5853020 (1998-12-01), Widner
patent: 6422088 (2002-07-01), Oba et al.
Suzuki Yasutoshi
Tanaka Hiroaki
Ellington Alandra N.
Noori Max
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