Gold Immersion Deposition on Electroless Nickel Substrates

An immersion gold-plating process on electroless nickel substrate was investigated. The effects of gold salt, trisodium citrate, bath temperature, and pH on the gold-immersion-deposition process are also discussed. The study was performed by measuring the mixed potential-time curves in situ and electrochemical impedance spectroscopy in combination with X-ray fluorescence spectrometry (XRF) and atomic force microscopy (AFM) surface analysis. Electrochemical measurements and XRF results show that both the deposition rate and the mixed potential changed during the gold-deposition process. These variations reflect the change of electrode surface state. AFM analysis shows that the morphology of nickel surface changed greatly at the initial stage of gold deposition. A model for understanding the gold-immersion-deposition process was proposed based on the experimental data. The effects of KAu(CN)(2), trisodium citrate, pH, and temperature on gold-immersion deposition are significant, via affecting the gold film formation and the deposition rate. The optimal conditions of aqueous solution for the gold-immersion plating were determined. The experimental results support the explanation of the proposed model. (c) 2007 The Electrochemical Society.