Fatigue Crack Growth Rate in 63Sn37Pb Solder Joints

Fatigue crack growth rate (FCGR) was determined in shear (Mode II) on notched 63Sn37Pb solder joints at room temperature. The FCGR data correlated reasonably well with the expression da/dN = B (ΔY)^b where ΔY was either ΔK, ΔJ, or ΔW_p. The value of b for ΔJ and ΔW_p was similar to that generally obtained for metals in Mode I loading; however, it was 2-3 times larger in the case of ΔK. Although the fatigue cracks initiated at the centrally located notches, they soon wandered toward the solder/Cu interface and then propagated in the solder adjacent to the intermetallic compound. The fatigue crack mode was transgranular with no clear microstructure preference. The results obtained on the notched specimens are in accord with those reported previously on initially smooth specimens tested in shear.