The use of surfactants and supercritical CO2 assisted processes in the electroless nickel plating of printed circuit board with blind via

With the high density and high precision requirement of electronic products, printed circuit boards (PCBs) are also facing the evolution into multilayer boards. Electroless nickel immersion gold (ENIG) is a process that is widely used in the surface treatment of PCBs. As a barrier layer, nickel plating is required even in the blind via of PCB to improve its corrosion resistance for further plating processes. In this study, different surfactants, mainly anionic surfactant, Sodium Dodecyl Sulfate (SDS) and cationic surfactant, Cetyl Trimethyl Ammonium Bromide (CTAB), are used to explore their possible effects on this electroless process. It is found that SDS improves the deposition rate in blind via plating and coating's surface roughness. The surfactants are also effective in increasing the corrosion resistance of the prepared coating. Furthermore, different plating processes, i.e. supercritical carbon dioxide (Sc-CO2) assisted electroless plating and post supercritical carbon dioxide assisted electroless plating, are investigated and compared with the conventional process. It is obtained that Sc-CO2 assisted plating has the best improvement in blind via deposition rate and better coating's corrosion resistance. The result is indebted to the fact that the bath mixed with Sc-CO2 has low surface tension of gas and high mass transfusion of liquid. This nature effectively increases the deposition rate of coating in the blind via, and also makes the surface of the coating smoother and more uniform. To further explore whether high temperature affects the corrosion resistance of the coating when it passes through the reflow oven in surface mount technology (SMT) soldering operations of PCB, the coating is annealed at different elevated temperatures up to 400 °C. The experimental results found that annealing enables the grain refinement of the plated layer, thereby enhances the corrosion resistance of the plated layer.