(163bq) Characteristics and Deposition Kinetics of Electroless Nickel-Tungsten-Phosphorus Alloys Plated from Slightly Basic Bath

Characteristics and deposition kinetics of electroless nickel-tungsten-phosphorus (NiWP) alloys plated from a slightly basic bath (pH 9) were studied. The resulted electroless NiWP deposits was characterized mainly with an SEM (JEOL JSM-6700F) equipped with an EDX, XRD (Rigaku RINT-2000) with Cu K1 radiation, =1.5406Å, as the incident x-ray source and a potentiostat for corrosive study. The composition distributions of the resulted electroless NiWP alloys reached their constant values quickly, e.g. within 10 min, after the onset of the deposition process. Langmuir adsorption isotherm is found adequately to correlate the composition of the electroless NiWP alloys and the bulk concentration of the corresponding constituent in plating bath. Our experimental results indicate that existence of Ni(0) on the plating frontier really enhances the adsorption of hypophosphite and tungstate anions in addition to Ni+2 ions, which in turn boosts the overall deposition process. In contrast, the W(0) in the alloys only increases the adsorption of tungstate anions, but not nickel ions and hypophosphite anions. Moreover, competitive adsorption between tungstate and hypophosphite anions was present during the plating process.