Failure Mechanism of Electrochemical Migration Silver Electrode on Negative Temperature Coefficient Thermistor in Intelligent Power Module

This Intelligent Power Module (IPM) plays an important role in the reliability of the whole machine. In the past, most people have studied the failure mechanisms induced by electrical stress and mechanical damage [1]. However, failure mechanism of electrochemical migration is little reported in IPM. This paper reports Ag sintered layer on negative temperature coefficient thermistor, increases the risk of obtaining metal migration in the hygrothermal environment. Firstly, five sets of evaluation of electrochemical migration have been designed and executed using temperature factor, humidity factor, silver and gold of electrode. Secondary, Electrical analysis and microstructure analysis of performed power module test samples were carried out using semiconductor curve tracer, optical microscope, scanning electron microscope and energy dispersion spectrum. It is found that the silver metal of the NTC electrode inside the IPM module occurs failure mechanism of the electrochemical migration at a humid environment, causing the partial voltage at both ends of the NTC to decrease. Moreover, decreasing of partial voltage has result in the reduction of the switching device inside the IPM. And the microstructure results show, dendritic compounds can be observed on the side of the all NTC and Ag and O elements were confirmed in the compounds. The results shows that the NTC of the silver electrode is easy to undergo electrochemical migration, resulting in the reduction of the NTC partial pressure at the humid environment. This study provides a method for evaluating reliability and guiding reliability improvement of IPM at humid environment.