Effects of substrate thermal expansion coefficient on the physical and electrical properties of thick film resistors

The way in which the difference between the thermal expansion coefficient of a thick-film resistor and that of an alumina substrate affects the physical and electrical properties of the resistor was examined. The difference between the thermal expansions produces a compression or a tension in the resistor. Consequently, the electric resistance and temperature coefficient of resistance of the resistor without the substrate are larger than those of the resistor with the substrate. In the case of a specimen of RuO₂-glass (10:90), the force acting on the resistive film from the substrate is about 1.88×10^-1 N in tension in the temperature range from 75°C to 125°C and about 1.55×10^-1 N in compression for the temperature range from -25°C to -50°C. The higher the resistance and the larger the thermal expansion coefficient of glass, the larger are the resistance changes