Characteristic evaluation of electroless nickel–phosphorus deposits with different phosphorus contents

The surface morphology, electrical property and reaction with solder alloy of two electroless nickel-phosphorus (EN–P) deposits (Ni–7wt.%P and Ni–10wt.%P) were investigated in this study. The P content of the EN–P layer decreased with increasing pH value. The EN–P plating layers had an amorphous structure and the electrical resistivity of the layer increased with increasing P content. Reaction layers of Ni3Sn4, Ni2SnP and Ni3P formed at the interfaces between the Sn–3.5Ag solder and the two EN–P deposit layers. The thickness of the interfacial Ni3Sn4 intermetallic compound (IMC) layer in the Sn–3.5Ag/Ni–7wt.%P joint was thicker than that in the Sn–3.5Ag/Ni–10wt.%P joint, whereas the thickness of the Ni3P layer increased with increasing P content. These study results confirmed that the interfacial reaction between solder and the EN–P layer is significantly affected by the composition (P content) of the EN–P layer.