Influence of phosphorous content on microstructure development at the Ni-P Plating/SAC interface

Abstract

Studies of the commonly used Ni-P surface finish of 4.3 and 11.6 wt. % of P content electroless plated on nickel substrates followed by their reaction with SAC305 solder were performed. It was demonstrated that the Ni-4.3P plating was crystalline, while the Ni-11.6P was mostly amorphous. The transformation of the Ni-P into Ni₃P phase took place at 672 K and 605 K for low and high P amount, respectively. The activation energy (E _a ) of the crystallization processes in the Ni-P plating was lower for the Ni-11.6P plating. Interaction of SAC305 solder with both types of the inspected plating showed the creation of (Cu,Ni)₆Sn₅ phase in the form of thin layer and large scallops, while for Ni-11.6P/SAC305 interface also (Ni,Cu)₃Sn₄ phase. The thickness of these phases was larger in the case of low phosphorous containing plating. The Ni-11.6P plating after the reaction with SAC305 totally transformed into Ni₁₂P₅, while the enrichment in P up to 10.5 wt. % occurred in the Ni-4.3P which did not lead to the appearance of any Ni_xP_y type phases. After the reaction of plating with solder the Ni₂SnP phase was not identified. This was related to the absence of spalling phenomenon of the intermetallics into solder.