Accurate Extraction Method for Thermal Resistance of Press-Pack Devices Based on Structural Function

Junction-to-case thermal resistance is one of the most effective means to evaluate the thermal characteristics of power devices. Press-pack devices have double-sided and asymmetrical heat flow paths on both sides. It is difficult to accurately locate the case position on both sides of the device and separate the junction-to-case thermal resistance using only the transient dual interface method. This paper proposes an effective heat capacity method based on a generalized one-dimensional thermal network, which establishes a correspondence between thermal resistance and heat capacity through structure functions, and decouples the heat flow channels on both sides according to the heat flow ratio on both sides, thereby accurately separating the junction-to-case thermal resistance of press pack devices. Experimental results indicate that the interference resistance of the effective heat capacity method to environmental temperature fluctuations is 30.85% higher than that of the transient dual interface method. Furthermore, the junction-to-case thermal resistance extracted by this method deviates by only 2.03% from the reference value under three-dimensional heat transfer, representing a 27.37% improvement in accuracy compared to the transient dual interface method.