Correlation between thermal fatigue and thermal anisotropy in a Sn-rich solder alloy

Intrinsic thermal fatigue in a mechanically unconstrained Sn-rich Sn-3.8Ag-0.7Cu alloy has been investigated under cyclic thermal loading within the temperature range of 293 K to 353 K. Fatigue damage resulting from this cycling is shown to occur preferentially along some grain boundaries. From a combination of orientation imaging microscopy and finite element modelling it appears that fatigue damage and stresses resulting from the thermal anisotropy of Sn are highly correlated.