Effect of surface structure on the contact resistance measurements of electrodeposits

It has been demonstrated with gray nickel phosphorus alloy (Ni/P) deposits and with gray nickel (NiCl) deposits that achieving consistently low R/sub c/ using base metal deposits requires a surface morphology with a multitudinous number of tightly space asperities of uniform height. These asperities, on a microscopic (5000*) scale, can appear to be acicular star-burst or gritty (sand-like) and will maintain low R/sub c/ as long as they meet the criteria of tight spacing and uniform size. Representative samples of these base metal gray deposits have maintained R/sub c/<10 m Omega after exposure to 50 degrees C and 95% relative humidity for nine months. In comparison, R/sub c/ values of standard nickel deposits from a Watts nickel bath were approximately 400 m Omega after only four days of exposure. To demonstrate that it is the surface microstructure of the deposit that yields the desirable R/sub c/ behavior, gray palladium deposits with an acicular surface structure similar to that of gray Ni/P deposits were investigated. In a relatively severe humid environment containing HCl, gray palladium deposits had lower R/sub c/ than wrought palladium.<
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