Effect of pulse plating parameters on electrical contact behavior of nickel coatings

Pulse and DC plated nickel coatings onto copper substrates were investigated in view of their use as underlayer in Au/Ni/Cu or as external protective coatings. Deposition parameters were varied in order to determine their influence on the microstructures - and consequently on the electrical contact properties - of the electrodeposited Ni films. XRD analysis, roughness and hardness measurements, as well as SEM studies were performed on these samples. Preferred orientation and microstructure changes were observed as current density and pulse plating frequency were increased. Smooth and dense coatings were obtained for high pause-to-pulse ratio, 25-75 Hz pulse-plating frequencies, and low current density. The contact resistances R_c of the as-deposited samples in approach and insert mode were measured versus load F_c in the range 0.1-10 N. It was found that initial contact resistance follows the power law R_c=KF _c^-n, where n is hardness and coating topography dependent. Moreover, aging samples in daily cyclic atmosphere shows an increase in contact resistance during the test, but ohmic behavior prevails as verified by current-voltage characteristics. Finally, mechanical behavior investigated by fretting study shows that the pulse reverse condition improves contact resistance stability