Study on the methods to measure the junction-to-case thermal resistance of IGBT modules and press pack IGBTs

The accurate measurement of the junction-to-case thermal resistance of Insulated Gate Bipolar Transistor (IGBT) devices is notably important for manufacturers to optimize the internal structure of packaging in order to improve its reliability and for users to take full advantage of the devices. The existing differences between IGBT modules and press pack IGBTs (PP IGBTs) not only in their packaging styles, but also in their working conditions may lead to some differences in the methods to measure their junction-to-case thermal resistance. In this paper, the junction-to-case thermal resistances of both IGBT modules and PP IGBTs have been measured using the traditional thermocouple method (steady-state method) and transient dual interface method (transient method). The applicability of these two methods for the measurement of junction-to-case thermal resistance of IGBT modules and PP IGBTs is summarized based on the experimental results. The steady-state method is suitable for the measurement of junction-to-case thermal resistance of IGBT modules, but not for PP IGBTs, because of the thermocouple inserted to measure the case temperature. The transient method is appropriate for the measurement of junction-to-case thermal resistance of not only IGBT modules, but also PP IGBTs, as a thermocouple is not required to measure the case temperature.