Lifetime and failure analysis of perovskite-based ceramic NTC thermistors by thermal cycling and abrasion combined stress

A perovskite-based ceramic NTC (negative temperature coefficient) thermistor was developed. A ceramic NTC thermistor was used for sensing the temperature of the heated roller from a laser printer. FMEA (failure mode and effect analysis) was applied to find the effective stress factor on the reliability of the sensor. System failure caused by the malfunction of a thermistor was studied. Possible failure modes, effective stresses that can lead to shortened lifetimes, and potential weak points of the thermistor were analyzed. The combined stress of thermal cycling and abrasion was found to be the most important factor among the listed effective stresses. The temperature profile of the thermal cycle was designed by taking into account the actual operating conditions, and an accelerated lifetime testing machine for estimating operational lifetimes was developed for the profile with a roller rotation. The lifetime of thermistor was estimated from the duration frequency of the thermal cycle using a lifetime testing machine with a roller rotation.