Reliability evaluation for specifying fatigue mode in power device

This paper presents a fundamental method to evaluate power cycle fatigue life of power device. Coupled electrical-thermal analysis is performed to obtain the distribution of temperature due to electric current. Then, thermal-mechanical analysis is carried out to calculate inelastic strain range generated in a solder joint. In addition, the fatigue evaluation for aluminum wire bonding was carried out simultaneities. Crack path simulation technique was used to evaluate total fatigue life in solder joint and resultant temperature increase. The fatigue life of aluminum wire bonding was estimated by the same model and the same approach. It was faucal the crack occurs at the central area of the solder layer below aluminum wire bonding. Then the maximum temperature in the solder grows up as crack propagation. As a result, the temperature increasing gives a big impact on the reliability of the aluminum wire bonding, and decrees the fatigue life. That is to say, this study is comparison between the fatigue life of solder joint and aluminum wire bonding for evaluate total life of the power device.