Reliability of Sn-3.5Ag solder joints in high temperature packaging applications

There is a significant need for next-generation, highperformance power electronic packages and systems with wide band gap devices that operate at high temperatures in automotive and electric grid applications. Sn-3.5Ag solder is a candidate for use in such packages with potential operating temperatures up to 200°C. However, there is a need to understand thermal cycling reliability of Sn-3.5Ag solders. The results of a study on the damage evolution occurring in large area Sn-3.5Ag solder joints between silicon dies and Direct Bonded Copper (DBC) substrates subject to thermal cycling between 200°C and 5°C is presented in this paper. Damage accumulation was followed using high resolution X-ray radiography techniques, and nonlinear finite element models were developed based on the mechanical property data available in literature to understand the relationship between the stress state within the solder joint and the damage occurring under thermal cycling conditions. It was observed that regions of damage observed in the experiments do not correspond to the finite element predictions of the location of regions of maximum plastic work.