The Autocatalytic Deposition of Gold in Nonalkaline, Gold Thiosulfate Electroless Bath

Abstract

The autocatalytic deposition of gold has been investigated in a novel, nonalkaline, noncyanide electroless gold plating bath. The bath consists of sodium L‐ascorbic acid as the reducing agent and sodium gold (I) thiosulfate as the gold complex. Ascorbic acid autocatalytically reduces gold thiosulfate at deposition rates of approximately 1 μm/h. The reaction sequence includes various side reactions responsible for consuming reactants and lowering the deposition rate. The rate of the electroless gold thiosulfate reduction is sensitive to the reactant concentration as well as the concentration of thiosulfate. The accumulation of thiosulfate and the depletion of the reactants explain the decreasing deposition rate with time. Periodic addition of hydrogen peroxide consumes the excess thiosulfate and increases the deposition rate and longevity of the bath.