Advanced Method of Pure Solder Layer Thermal Resistance Measurement in Power Cycling

Solder layer degradation is one of the typical failure modes of power electronics after power cycling and assessed by measuring the junction-to-case thermal resistance, with a 20% increase criterion. The degree of solder layer degradation at a 20% increase in thermal resistance varies considerably between devices in the power cycling., as the thermal resistance of devices themselves are different. An advanced method for accurately extracting the thermal resistance of pure solder layer based on the theory of thermal physics is proposed in this paper., which provides a more accurate representation of the solder layers degradation than traditional junction-to-case thermal resistance measurement. Firstly., this paper establishes the theoretical basis for the accurate extraction of solder layer thermal resistance in conjunction., and analyses the theoretical values of the monitoring windows selected in the proposed method. Then., Infineon's EasyPACK module (FS25R12W1T4) is selected to verify the feasibility of the method through power cycling tests. Finally., the effectiveness of this advanced method is well verified., even for different voltage classes.