Lifetime prediction of solders in electronic packaging

The repeated mechanical loading of connecting solder joints caused by thermal cycling of electronic assemblies through differential thermal expansion among assembly members may lead to fatigue failure. The rate of fatigue damage is determined by the solder stress/strain state, temperature, frequency, hold time, and environment. Failure can be induced by defect crack propagation or yield. The mechanism of the damage is complex, especially when such materials are operating in high temperature environments, and is far from being understood. The mechanical properties may be altered due to high temperature, and different levels of the internal structure are found to take control under different conditions. In this paper, three useful methods for the investigation of fatigue of solder materials are compared. The crack behavior analysis of Subrahmanyan et al (1989), the energy approach of Vaynman and McKeown (1993), and the continuum mechanics approach of Zubelewicz (1993) for the inelastic deformation of ductile materials are discussed.