Effect of surface structure on the contact resistance measurements of electrodeposits

Gray nickel phosphorus alloy (Ni/P) deposits plated from a nearly neutral pH ammoniacal bath and gray nickel deposits plated from an acid chloride bath (Ni(Cl bath)) were investigated. These deposits were shown to have a surface morphology with a multitudinous number of tightly spaced asperities of uniform height, while consistently maintaining low R/sub c/ (contact resistance). Representative samples of these nickel deposits have R/sub c/ values less than 10 m Omega after exposure to 50 degrees C and 95% RH for 9 months. The intensity of the gray color of the Ni/P and Ni(Cl bath) deposits directly correlates with their R/sub c/ values. Scanning electron microscope photographs showed that the asperity size of Ni(Cl bath) deposits increases and the shape becomes rounder at higher current densities, from predominantly acicular knife-edge like at 25 A/ft/sup 2/ to boulderlike at 150 A/ft/sup 2/. The contact resistance behavior of palladium deposits with similar surface morphology was also examined after exposure to a corrosive environment.<>