In situ-Raman spectroscopy and electrochemical characterization on electroless nickel immersion gold process

Electroless nickel immersion gold (ENIG) process is one of the most used selective finishing in PCB production. It involves two different electroless deposition mechanisms: (1) NiP autocatalytic deposition and (2) gold galvanic plating where coating is obtained by a displacement reaction. Because during the ENIG process, NiP is dissolved from the electrode surface into the solution, it can be considered as a controlled corrosion process. For this reason, selection of the complexing agents in solution is crucial. Since they are the most used complexing agents, in this study EDTA and citric acid have been selected. In order to understand their effects on the NiP surface during the immersion plating, open circuit potential and potentiodynamic detection measurements have been performed. Furthermore, to establish which complexes are adsorbed on the electrode surface during the plating process, in- situ Raman spectroscopy was performed. Electrochemical and spectroscopic analyses reveal that EDTA is the dominant complexing agent, while citric acid is mainly a buffering agent.