Improvement of Power Cycling Life under Typical Operating Conditions of a Power Semiconductor Module by Sn-based Solder Die Bonding

In order to meet the market demand for higher power density of power modules, it is important to improve the power cycling life of die bonding solder because the maximum current is limited by the power cycling life. We analyzed the mission profile of typical railway applications, establishing that the thermal load with short power on-time and small temperature amplitudes occur frequently. We estimated and compared the life of Sn-based solder die bonding and Pb-based solder die bonding under an assumed mission profile. In the life estimation, we considered a peculiar phenomenon of Sn-based solder, the “vertical crack”. A life prediction formula was constructed based on the physical phenomenon of “vertical crack”. The expected longer life of power semiconductor modules adopting Sn-based solder was validated not only under conventional power cycling bench testing but also through actual operation. Sn-based solderedmodules can sustain higher maximum currents during actual operation than conventional Pb-based soldered modules. For example, if the target life is 30 years, the maximum currents can be improved by 50% under a typical operating condition.