Study of the Effects of Additives on an EDTA-2Na Electroless Ni-P Plating System

The effects of additives on the deposition rate, surface morphology, Ni and P elemental content of the electroless plating layer, and roughness of the electroless plating Ni-P layer were investigated. In an electroless plating Ni-P system, ethylenediaminetetraacetic acid disodium salt (EDTA-2Na) and sodium hypophosphite monohydrate were used as the complexing agent and reductant, respectively. The linear sweep voltammetry (LSV) polarization curve results showed that the compound addition of 1.0 mg L⁻¹ L-tyrosine, 2.0 g L⁻¹ saccharin, and 6.0 mg L⁻¹ sodium dodecyl sulfate (SDS) could inhibit sodium hypophosphite oxidation and nickel ion reduction, which eventually reduced the Ni-P deposition rate. The Tafel polarization curves indicated that the compound additives obviously improved the corrosion resistance of the Ni-P electroless plating layer. Field emission scanning electron microscopy (SEM) images showed that the composite additives generated fine and uniform Ni-P electroless plating particles and enhanced the density, eliminated the surface cracks, and reduced the pinholes on the electroless plating layer surface. Atomic force microscopy (AFM) tests showed that the addition of complex additives improved the smoothness of the plated layer, the R_a value was reduced from 135.0 nm to 53.2 nm, and the R_q value was reduced from 164.0 nm to 93.0 nm. The final composition and implementation conditions of the EDTA-2Na-based Ni-P electroless plating system were determined. The deposition rate was 10.44 μm h⁻¹, the P content of the electroless plating layer was 2.2%, and the electroless plating player was silver-white and bright.