Effects of Hold-Time on Thermal Fatigue Life of Solder Joints.

Abstract

The fatigue life estimation of solder joints is one of the most critical requirements in the development of reliable electronic components. Since the electronic components are subject to temperature variations under field conditions with a trapezoidal wave, it is important to obtain quantitative knowledge regarding the effects of hold-time on fatigue life. In this study, we first carried out low cycle fatigue tests using thin-walled cylindrical specimens. The specimens were subjected to strain controlled loading conditions with a trapezoidal wave and a variable strain rate wave in consideration of stress relaxation and elastic follow-up phenomena. It was confirmed that the fatigue life of the 63Sn-37Pb solder can be uniformly evaluated using an inelastic strain range and Coffin-Manson equations when the strain rate is low. Second, elastic-creep stress analysis was carried out for solder joints in a TSOP (thin small outline package). It was shown that the increase in creep strain during hold-time has a noticeable effect on the fatigue life under field conditions. Thus, careful consideration of creep deformation is essential, and consequently stress analysis based on the elastic-creep model can serve as a fatigue life estimation method in the reliability design.