Stability Study of Thick-film Pressure Sensor on Steel Substrate

Thick-film pressure sensors on steel substrate are proven to be robust and low cost, and can be used in many fields such as automotive industries, oil industries and military sectors. In this paper, finite element method (FEM) was used to evaluate residual thermal stresses and the self-heating of the thick film resistors (TFRs) on the offset voltage of the sensor. Results show that the residual stresses will affect the sensor output stability and accelerate the failure of dielectrics on steel substrate. The effects of self-heating of TFRs on the offset voltage can be negligible. Certain accelerated environmental tests are used to evaluate the robustness, stability of the sensors. Results show that the sensors have a stable output at constant temperature of 25 degrees C. Most sensors have a small offset change after thermal cycling. Although some sensors have a relatively large zero drift after thermal cycling, and this drift can be relieved by appropriate heat treatment. Finally, thermal shock test and drop test have verified the robust bonding between the dielectrics and the steel substrate.