Creep-fatigue modelling for solder-joint reliability predictions including the microstructural evolution of the solder

A model is developed for the effect of microstructural evolution (precipitation and dissolution of tin particles) during the thermal-cycling fatigue of low-tin, lead-tin solders. It is shown that the effect of changing the cycle frequency is intertwined with the effect of change the cyclic temperature limits. Because both the precipitation rate and the dissolution rate depend on temperature, it is expected that the boundary between low frequency and high frequency depends on the temperature limits involved. The situation is complicated by the fact that the dissolution rate depends not just on alloy composition and dissolution temperature, but also on the temperature at which precipitate structure was formed. A proper estimate of the frequency boundary must take this into account. It is concluded that a proper extrapolation of the mechanical behavior from one set of conditions to another must take the microstructural evolution into account