A comparative fatigue study of solder/electroless-nickel and solder/copperinterfaces

The fatigue resistance of the interface between electroless-nickel and the eutectic tin-lead solder alloy was examined in the as-reflowed and aged con ditions and compared to fatigue behavior of the copper/solder interface und er the same conditions. In the as-reflowed state, the fatigue resistance of the solder/electroless-nickel interface was slightly superior to that of t he solder/copper interface. However, after long-term aging, the fatigue res istance of the solder/electroless-nickel interface became far worse in the high crack growth rate regime. Examinations of interfacial microstructures and crack growth mechanisms indicated that the differences in fatigue resis tance between the two interfaces were not directly related to the thickness of the intermetallic phase at the interface, as commonly believed, but wer e due to differences in crack growth mechanisms.