Role of tin as a stabilizer in an electroless nickel-boron plating bath: Electroless NiB-Sn alloys properties.

The effect of tin chloride on bath stabilization and properties of electroless Nickel-Boron (NiB) coatings was investigated. NiB coatings were synthesized by electroless deposition using SnCl2 stabilizer. Sn was codeposited in the coating generating a novel NiB-Sn alloy. The deposition of NiB-Sn occurred in an aqueous bath containing a reducible metal salt (NiCl2), reducing agent (NaBH4), complexing agent (C2H4(NH2)2) and stabilizer (SnCl2). The pH was controlled at pH 12±1 in order to avoid bath destabilization. The stabilizer properties of SnCl2 were proved by the fact that the plating completely stops at high concentrations. The deposition was performed with three different concentrations of SnCl2 (0.05g/L, 0.1g/L and 0.2g/L). The morphological features are modified as a function of concentration. Coatings with finer cauliflower structure and more homogeneous thickness are reached with the increase of stabilizer concentration. Results for samples with 0.1g/L of SnCl2 show hardness (842 hk50) wear behavior (Ws 0.11 µm2/N) and scratch test (Lc 30N) results comparable to those presented by NiB-Pb coatings. These coatings are an environmentally friendly bath alternative to NiB-Pb and NiB-Tl coatings, respecting ELV 2000/53/EC and RoHS 2002/95/EC compliance.