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

Abstract

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 Ni 3Sn 4, Ni 2SnP and Ni 3P formed at the interfaces between the Sn–3.5Ag solder and the two EN–P deposit layers. The thickness of the interfacial Ni 3Sn 4 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 Ni 3P 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.