Effect of stress triaxiality on damage evolution of porous solder joints in IGBT Discretes

Abstract In this paper, the effect of stress states on the damage behavior of Sn-based solder connection in an IGBT discrete during thermal cycling (−40 °C to 160 °C) was investigated. To achieve the accurate results in FEM simulation, the porous solder layer based on the presence of micro-voids with blind mode was designed. The simulation shows that the micro-voids trap strain increment at the edges of solder layer and create a region with high strain density. It is also found that the low Von Mises stress at −40 °C is due to the limited ability of solder to creep at low temperature. At the peak temperature, the positive triaxiality factor (tension mode) dominates in the solder connection and intensifies the damage progression. The tension mode also leads to the void growth and coalescence phenomenon. According to the triaxiality analyses, the sharp curves of void boundaries along with the edges of solder layer are the most susceptible sites for crack initiation. It is also revealed that the stress triaxiality concentrates on the middle of solder during heating stage of thermal cycling while in cooling stage, it is localized at the edges.

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