Investigation on failure behaviour of solder joint during thermal fatigue

In SMT, the investigation on solder joint´s failure is always very important. Thermal fatigue is the main failure form for solder joint in SMT. In this paper the failure process of solder joint in SMT was investigated by both electrical resistance measurement method and crack observation method together. The characteristics of electrical resistance value variation of lead-tin and lead-free solder (SAC305) joint during thermal fatigue test were obtained. And at the same time the crack propagation in solder joint was observed. According to this, the failure rules of lead-tin and lead-free solder joint were compared. And by FEM, the relationship between electrical resistance value variation and crack propagation of solder joint during thermal fatigue test was studied, through which an criterion based on electrical resistance value variation for solder joint´s failure during thermal fatigue test could be obtained from experience. It was shown from experimental results that the lead-free solder (SAC305) joint had a higher resistibility from thermal fatigue than the traditional lead-tin eutectic solder joint. And the criterion based on electrical resistance value variation was built up from the experimental and simulation results.