THE IMPACT OF SUBSTRATE ROUGHNESS ON POROSITY - A COMPARISON OF ELECTROPLATED PALLADIUM, PALLADIUM-NICKEL AND COBALT HARD GOLD

The porosity of electroplated deposits is known to be related to certa in substrate conditions, such as inclusions, purity, and particularly, roughness, As few commercial substrates are finely polished, a means of understanding the impact of surface finish was desired, A compariso n of porosity was made between electrodeposited palladium, palladium-n ickel (80/20) and cobalt hard gold over varying degrees of substrate r oughness and deposit thicknesses, OFHC copper disks were abraded to va rious degrees of roughness from 0.05 to 1.0 mu m (center line average) , These samples were then plated with individual layers of the metal o f interest under controlled, highspeed conditions using a Rotating Dis k Electrode. Thicknesses ranged from 0.25 to 2.0 mu m. The plating con ditions were determined previously in order to produce minimal levels of intrinsic porosity from each of these specific chemistries, Porosit y was determined by subjecting the plated disks to sulfurous acid vapo r according to ASTM B799-88 (Standard Test Method for Porosity in Cold and Palladium Coatings by Sulfurous Acid Vapor) and subsequently to v apors of ammonium sulfide, The pore corrosion was tallied and reported as a percentage of salt-covered area for the various conditions.