Measurement of the Thermal Impedance Matrix of Power Modules by the Modulation Method

The article describes the experimental results of measuring the thermal impedance matrix of power MOSFET modules which characterizes cross couple thermal resistances of transistors of the module. The matrix elements measurements are based on the method using the device under test (DUT) heating by harmonically varying power and measuring the temperature response to such impact. The measurements were performed by the thermal impedance meter, which allows to heat every transistor of the power module and to measure the temperature response of the other transistors. The measurement of the thermal impedance matrix components was done by the analysis of the thermal impedance on modulation frequency dependence. Using the obtained values of the matrix elements, the junction temperature ${T}_{\text {j}}$ was calculated for all transistors of the module when an arbitrary pair of transistors was heated. The calculation results are in good agreement with the results of direct measurement of ${T}_{\text {j}}$ , which confirms the correctness of the obtained results of measuring the elements of the thermal impedance matrix. This method can be used not only for MOSFETs or insulated gate bipolar transistors (IGBTs) but also for hybrid integrated circuits and monolithic microwave integrated circuits.