Improved Thermal Impedance Measurement for Power Modules based on Thermal Imaging of the Baseplate

Abstract:
This paper introduces an improved method of measuring thermal impedance in power modules. It is based on the common VCE(T)-method for fast recording of the junction temperature but uses an infrared camera for detecting the baseplate temperature of the power module instead of a slow thermocouple. The measurement setup neither requires an additional heatsink nor any thermal interface material and thus allows more freedom with regards to the definition of the reference area on the baseplate. The developed routine also allows to correlate the forward voltage drop to a specific chip temper-ature without a time-consuming additional calibration routine on a heating plate. For realization of the novel measuring concept, a custom test bench was set up, which ensures proper synchronization of the load current, thermal imaging and voltage measurement. Validation measurements show good agreement with simulation data. The precision of the setup allows to quantify the thermal influence of packaging changes for power modules.