Exploring the water-soluble phosphine ligand as the environmentally friendly stabilizer for electroless nickel plating

Abstract

Phosphine (R3P) compounds being a typical type of coordination ligand used in homogeneous catalysis are known to possess a tunable affinity with the nickel atom. As such, it deserves to be studied whether a water-soluble phosphine ligand could also be used as a plating stabilizer in the electroless nickel plating (ENP) system in place of hazardous Pb(II) salt and what will be the unique effects generated due to this replacement. Triphenylphosphine-3, 3′,3″-trisulfonic acid trisodium salt (TPPTS) was then chosen as a model phosphine stabilizer to perform the study. TPPTS could indeed work to prevent the ENP process from running out of control. In addition, unlike the existing ENP stabilizers, TPPTS does not reveal a percolation concentration for a sharp ceasing of plating. Also according to the voltammetry investigation, TPPTS can be classified as a cathodic stabilizer. A Ni-P plating layer with high phosphorus content (> 15%) has been achieved using 10-4 mol/L TPPTS in the plating bath. Furthermore, this work investigated the relation between P weight percent and corrosion resistance of either the as-plated or the annealed Ni-P plating layer by electrochemical impedance spectroscopy (EIS). The annealing was found, according to the depth profile analysis, to drive diffusion of both Ni and P toward the bulk phase, which strongly revamps corrosion resistance of the plating layer. Finally, the stability of the ENP bath was evaluated using the metal-turnover (MTO) test. © 2009 American Chemical Society.