THE AUTOCATALYTIC DEPOSITION OF GOLD IN NONALKALINE, GOLD THIOSULFATEELECTROLESS BATH

The autocatalytic deposition of gold has been investigated in a novel, nonalkaline, noncyanide electroless gold plating bath. The bath consi sts of sodium L-ascorbic acid as the reducing agent and sodium gold (I ) thiosulfate as the gold complex. Ascorbic acid autocatalytically red uces gold thiosulfate at deposition rates of approximately 1 mu m/h. T he reaction sequence includes Various side reactions responsible for c onsuming reactants and lowering the deposition rate. The rate of the e lectroless gold thiosulfate reduction is sensitive to the reactant con centration as well as the concentration of thiosulfate. The accumulati on of thiosulfate and the depletion of the reactants explain the decre asing deposition rate with time. Periodic addition of hydrogen peroxid e consumes the excess thiosulfate and increases the deposition rate an d longevity of the bath.