The Aging Behavior of Commercial Thick-Film Resistors

An earlier paper reported the promising prospects of accelerating thick-film resistor aging by elevated temperature and humidity stress; those early findings have now been confirmed by further results from many thousands of hours of overstress testing of commercially produced resistors from various sources--amounting to accumulated test times of some millions of resistor-hours. The normal aging trend is a steady increase in resistance at a rate influenced by various factors such as manufacturing origin, resistivity, electrical bias, environment, and encapsulation. The majority of the increases vary with the square-root of time, consistent with a diffusion-controlled degradation of the conduction processes. Some changes also conform to piezo-resistive effects and together these provide physical explanations for the aging behavior of thick-film resistors. The drift observed in the majority of resistors can be extrapolated to give a prediction of less than 0.5 percent change in 20 years operation in standard environments---a heartening prospect indeed for thick-film reliability.