Low-cycle fatigue failure behavior and life evaluation of lead-free solder joint under high temperature

In this study, low-cycle fatigue test was conducted for a lead-free solder joint at two test temperatures (348 K, 398 K) and three strain amplitudes (3%, 4%, and 8%). Fatigue failure behavior was analyzed and the fatigue life was evaluated using the Coffin-Manson relationship and Morrow energy-based model. The results show that the maximum load gradually drops with increasing the number of loading cycles. When the strain range or temperature is low, the maximum load drop curve can be divided into three stages. Then, it degrades into a linear stage with increasing the strain range or temperature. Both the softening of solder and the reduction of effective load-bearing area are responsible for the maximum load drop depending on the test condition. Fatigue crack initiates at the corner of the solder joint and propagates along the strain concentrated zone. Spacing distance between fatigue striations is enlarged with increasing the temperature in accordance with the degradation of fatigue resistance. In addition, both the Coffin-Manson model and Morrow energy-based model can be used to evaluate the fatigue life of solder joint under high temperature. The fatigue ductility exponent α in Coffin-Manson model and the fatigue ductility coefficient C in Morrow model are dependent on temperature, whereas other parameters in these two models keep stable under different temperature.