Electrodeposition of Mirror-Bright Silver in Cyanide-Free Bath Containing Uracil as Complexing Agent Without a Separate Strike Plating Process

A cyanide-free silver plating bath containing uracil as a complexing agent was investigated. The electrochemical properties of a silver complex were studied on a disk glassy carbon electrode by means of cyclic voltammetry and a rotating disk electrode. The brightness and adhesion of silver deposits obtained from this silver plating bath onto copper substrates in the absence and presence of polyethyleneimine (PEI) were evaluated. Mirror-bright and good adherent silver deposits could be obtained without a separate strike plating process when PEI as an additive was added. Differential capacitance studies indicated that competition adsorption between PEI and uracil molecules occurred on the silver surface. The electrochemical displacement rate of silver by base metal (e.g., copper) was very slow compared with that in a typical cyanide strike bath from the results of electrochemical quartz crystal microbalance studies. The surface morphology of silver deposits characterized by scanning electron microscopy illustrated that, with the addition of PEI, the grain size of the deposits decreased from hundreds to tens of nanometers.