Comparison study of gold coatings prepared by traditional and modified galvanic replacement deposition for corrosion prevention of copper

Abstract

Gold coating is one of the choices to prevent copper circuit in PCBs from corrosion. Although galvanic replacement deposition is supposed to be a convenient method to prepare gold coating on copper circuit, compact gold coating is hard to be obtained through traditional galvanic replacement deposition. In this work, gold coatings were prepared on copper substrates through traditional and modified galvanic replacement deposition. According to the SEM, EDS, XPS and XRD tests, the gold coating prepared by traditional galvanic replacement deposition had lots of micropores and nanopores, and Cu-Au solid solution phase was generated on copper substrate other than the gold phase. Therefore, the gold coating prepared by traditional galvanic replacement deposition could not prevent copper substrate from corrosion, but slightly increased the corrosion current density of copper substrate in 3.5 wt% NaCl solution owing to the galvanic corrosion. However, compact gold coating could be obtained through modified galvanic replacement deposition, in which aluminum foil was contacted to the copper substrate to form galvanic couple and donated the electrons for the deposition of gold instead of the copper substrate. The SEM, EDS, XPS and XRD tests demonstrated the gold coating prepared by modified galvanic replacement deposition was compact and mainly composed of pure gold phase. The gold coating prepared by modified galvanic replacement deposition obviously enhanced the corrosion resistance of copper substrate, and it reduced the corrosion current density of copper substrate in 3.5 wt% NaCl solution to 1.773 μA·cm−2 from 87.40 μA·cm−2 with the corrosion inhibition efficiency of 98.0%.