How materials behaviour affects power electronics reliability

Life-time of power electronics assemblies is limited, mainly due to the numerous thermal cycles experienced in the mission profile. Differences in thermal expansion coefficients (CTE) of materials cause fatigue degradation, both in active power cycling as well as in passive ambient or cooling medium temperature cycling. To understand the load and the degradation mechanisms due to thermal cycling, thermal-mechanical models are presented to assess the materials behaviour. Models and calculated results will be presented for the bond-wire lift-off failures and for crack propagation in large-area solder joints. Reasonable agreement with available experimental data has been achieved.