Improving Impact Toughness of BGA Lead-Free Solder Joints by Using Higher Current Density in Electrolytic Ni Plating

Improving the toughness against impact of an electrolytically plated (Ni/Au) Sn-3 mass%Ag-0.5 mass%Cu solder joint for a ball grid array package was examined. The concentration of impurities (C, O, S, and Cl) that reduce the toughness against impact of Ni plating is shown to be inversely proportional to the rate of Ni deposition. The constant of proportionality becomes the rate of adsorption of impurities and depends on how clean the plating bath is. These results indicate that the concentration of impurities in Ni plating can be controlled by the rate of deposition (or current density). Creating the plating at a higher current density from a depth of about 1 μm from the finished surface is shown to improve the toughness against impact of solder joints formed with the combination of Ni plating and Sn-3 mass%Ag-0.5 mass%Cu solder. This method improves toughness against impact while suppressing variation in thickness of the Ni plating.