Electroless Nickel Plating and Process Simulation for Surface Treatment

The acidic electroless nickel plating on copper with sodium hypophosphite as the reducing agent is highlighted and discussed herein in a comparative study with the alkaline nickel plating with hydrazine as reductant. Experimental evidence suggest that the acid nickel plating layer is thicker and fully adhered, with poor crystallinity, and contains phosphorus nickel and phosphorus in composition. The alkaline nickel-plating film displays a poor quality of coverage, with a loose and thin coating, but its crystallinity is better and it is pure nickel. It is found the plating thickness is not uniform around the cylinder sample, larger on the upper surface and small or nothing on the underneath surface. Electrochemical tests showed that in the alkaline solution, a lower mixed potential and larger deposition current density would promote the deposition, however, the reaction did not occur on the sample surface because of the vigorous homogeneous precipitation of Ni. Furthermore, the deposition process of hypophosphite reducing nickel is simulated through the finite-element electrochemical method. The relationship between the coating thickness and multiple positions around the sample surface is compared as a function of the plating time. The simulated results show that the plated Ni thickness varies with the positions probably due to the limited diffusion of chemical species, which is consistent with the experimental findings.