Thermal stability of electroless-nickel/solder interface: Part B. Interfacial fatigue resistance

The relationship between fatigue resistance and interfacial microstructure was studied along the interface between the Sn-Pb eutectic alloy and an ele ctroless Ni-P coating. The fatigue resistance of the solder interface was m easured from the flexural peel fracture mechanics specimens in the as-reflo wed, mild-aged, and overaged conditions. While the mild aging had only a ma rginal effect on the fatigue resistance of the interface, overaging was fou nd to significantly degrade the interfacial resistance to fatigue-crack,gro wth, resulting in a lower fatigue threshold and a much earlier onset of the fast fracture. The effects of the overaging were shown to result from the transformation of the interfacial microstructure, which weakened the crack- sliding resistance in the near-threshold regime and embrittled the interfac e in the high crack-growth rate regime.