Power Modules Lifetime Estimation Under Compound Tests

Reliability assessment of IGBT power modules increasingly requires test conditions that reflect field operation, where the semiconductor devices are subjected to simultaneous fast junction temperature fluctuations and slow baseplate or heatsink temperature variations. Conventional power cycling tests consider these thermal loads separately and therefore fail to capture potential interaction effects that can critically shorten the lifetime. This work investigates experimentally the superimposition effect of active High Frequency (HF) and passive Low Frequency (LF) thermal cycles using dedicated compound tests, provides an analysis of the physical mechanism responsible for the observed lifetime reduction. Active cycles are generated through high-frequency DC current injection, producing junction temperature swings in the range of 30°C-70°C with cycle times of 150ms-18s, while passive cycles are imposed through controlled heatsink temperature variations of 85°C-145°C with time periods from 12min to 1h17min. Failure analysis identifies wire bonds lift off as the dominant degradation mechanism under these compound conditions. Application of conventional Rainflow counting algorithm and Miner's rule overestimate significantly the measured lifetime by a factor exceeding seven, revealing a degradation acceleration due to high- and low-frequency cycles interaction. To explain this effect, an analytical model is developed and qualitatively validated by Finite Element (FE) simulations. The model captures alternating ratcheting phenomenon as a responsible of the observed lifetime reduction, and despite the long and detailed temperature profiles of compound tests, it achieves highly shorter computation times compared to FE approach. The proposed methodology provides an efficient tool to account for superimposed thermal cycles interactions and enhances reliability assessment for power electronic devices.