Enhancement in the Deposition Behavior and Deposit Properties of Electroless Ni-Cu-P

This work describes as an attempt to improve the deposit properties of electroless Ni-Cu-P deposits by controlling the deposition condition and the composition of the plating solution. Tensile internal stress induced by hydrogen evolution during electroless Ni-Cu-P deposition was manipulated by controlling deposition conditions such as stirring and zincating. The stirring action releases the hydrogen-induced stress and improves adhesion of the deposit in the condition of once zincate pretreatment. It was also attempted to vary the concentration of reducing agents (NaH₂PO ₂·H₂O), buffering agents (NH₄Cl), and complexing agents (Na₃C₆H₅O ₇·2H₂O) of the plating solution to improve the deposition rate, crystallinity and the composition uniformity of Ni-Cu-P deposits. The results show that a decrease in complexing agents results in steadier deposition of Ni and Cu elements and higher deposition rate. The preferable deposition solution consists of 0.057 mol/L NiSO ₄·6H₂O, 0.0008 mol/L CuSO ₄·5H₂O, 0.14 mol/L NaH₂PO ₂·H₂O, 0.07 or 0.09 mol/L Na₃C ₆H₅O₇·2H₂O, and 0.75 mol/L NH₄Cl at pH 8.0, which creates amorphous and uniform Ni-Cu-P deposits.