Correlation between thermal fatigue and thermal anisotropy in a Pb-free solder alloy

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