Effects of internal stresses on the thermomechanical behavior of Sn-based solder joints

Solder joints are multi-component systems with several entities. When such a joint is subjected to a temperature excursion during service, large stresses can arise due to different coefficients of thermal expansion (CTE) of components that make up the joint. The magnitude of stresses that can develop not only depends on the temperature differences encountered, but also on rates at which such changes are imposed and the dwell times at the temperature extremes. Severe anisotropy of tin, and constraints imposed by the entities present in the joint on the solder behavior, also play significant roles in the development of these stresses in tin-based solder joints. Since the extents of internal stress build up is dependant on material behaviors, such as strain-rate sensitivity, stress relaxation, etc., adaptation of service parameters, such as, heating/cooling rates and dwell times at temperature extreme during TMF are viable options to minimize the internal stress. Since solder is at a high homologous temperature during service, the predominant damage mode is grain boundary sliding and presence of submicron size stable reinforcements that are strongly bonded to the Sn grain boundary is a suitable means to reduce TMF damage.