Nickel phosphorus alloys as electrical contact material--Part II. Factors for producing low contact resistance.

As more electronic products become disposable because it is cheaper to replace than to repair, the product life cycle becomes shorter and shorter and the need for a low cost electrical contact material for use in separable connectors in these products becomes greater than ever. One promising candidate is a nickel phosphorus alloy (Ni/P) plated from a neutral ammoniacal bath. The objective of the present investigation was to determine the factors that produce the low C.R. because an understanding of these factors should also reveal the limitations of this Ni/P coating. The surface morphology of the gray colored Ni/P deposits appears to be the predominant factor in producing low C.R. The gray deposit consists of a multitudinous number of tightly spaced microscopic star-like asperities of relatively uniform height when viewed at a magnification of 2000. This structure may assist in breaking through any oxide or other insulating film on the base metal deposit and in inhibiting the subsequent ingress of oxygen or other contaminants that would affect the intimate a-spot contacts provided by the protrusions.