The role of Bi 3+ ‐complex ion as the stabilizer in electroless nickel plating process

Bi 3+ ‐complex ion is presented here as a less toxic stabilizer for use in electroless nickel plating (ENP) to replace the existing Pb 2+ ion stabilizer. The asymmetric derivatives of EDTA are identified to be a type of coordination ligands that can combine with Bi 3+ ions to form soluble complexes in the acidic ENP solution. In the ENP system studied the Bi 3+ ‐complex ion displays a critical stabilizer concentration of about 10 −5 mol/L, that is, the percolation concentration over which the ENP rate drops sharply. Besides the experimental measurement, deposition rates of both Ni and P are also simulated by using a kinetic model that has been derived from the double electric layer theory. The Bi 3+ ‐complex ion, behaving like conventional Pb 2+ ion, stabilizes ENP bath through the chemical replacement reaction at the surface of Ni deposition layer and results in a passive plating surface. This investigation also verifies the properties of the EN deposit, which are insignificantly affected by the length of service time of the plating solution by employing Bi 3+ ‐complex ion stabilizer. © 2009 American Institute of Chemical Engineers AIChE J, 2009