Reliability Evaluation and Failure Analysis for NTC Thermistor

Abstract

Failures of NTC thermistor are analyzed. Visual inspection, electrical parameter test, non-destructive test, and destructive physical analysis were performed on the field samples to identify the root cause of failure. It was found that the predominant failure mechanism was the copper migration of dumet (copper-clad alloy) at glass-PVC interface for glass-coated chip type NTC thermistor molded with PVC. Next, an accelerated life test is designed to predict the lifetime. Temperature, voltage, and humidity are considered as accelerating variables. Under the assumptions of a general life-stress relationship and Weibull lifetime distribution, the parameters of life-stress relationship and acceleration factor for the migration are estimated by analyzing the test data.