Thermal Analysis of SiC Power Semiconductor Packages using the Structure Function

This paper presents a comprehensive analysis on the information contained within the structure functions of SiC power MOSFET packages, focusing on the regions of die and die attach layer. It is shown that the structure function is affected by: 1) the square-root-t approximation of the missing part of the measured thermal impedance, 2) the temperature-dependent package material properties, 3) the thermal coupling between parallel dies in a multi-chip power module (MCPM), and 4) the nonuniform degradation of die attachment layers in the MCPM estimated by a common temperature-sensitive electrical parameter. All effects are quantitatively determined using calibrated electrothermal COMSOL models of a discrete commercial SiC power MOSFET package and a multichip half-bridge SiC power MOSFET power module designed and fabricated in-house.