Electroless Deposition of Ni-Sn Layers Having High Sn Content (>30 at.%) on Fe Substrates (1)

～ Optimization of Bath Composition for Ni-Sn Tin Film ～

Abstract

Nickel（Ni）-tin（Sn）layers were electroless-deposited on iron（Fe）substrates from baths containing nickel sulfate（NiSO₄）, sodium citrate（Na₃C₆H₅O₇）, and sodium stannate（Na₂SnO₃）with sodium hypophosphite（NaH₂PO₂）and dimethylamine-borane（C₂H₇N･BH₃）as reducing agents. By optimizing the bath composition, 0.4-0.8-μm-thick Ni-Sn layers with atomic Sn content of 40-50% were formed on the Fe substrates during 20-min deposition. The Sn content in Ni-Sn layers achieved in this study is the highest ever reported. Analyses by X-ray photoelectron spectroscopy（XPS）and X-ray diffractometry（XRD）confirmed uniform dispersion of Ni and Sn atoms in the layer and indicated the Ni-Sn layers as the main structures of Ni_1.5Sn. A bath prepared with a C₂H₇N･BH₃ reducing agent exhibited durability for Ni-Sn layer electrodeposition persisting up to eight times as long as that prepared using NaH₂PO₂. Chemical resistance property tests indicated that Ni-Sn layers prepared with NaH₂PO₂ had high resistance against 25 wt.% hydrogen peroxide（H₂O₂）aqueous solution. No dissolution of the Ni-Sn layer or Fe substrate was observed for 72 h.