Effect of boron content in electroless Ni–B layer on plating layer properties and soldering characteristics with Sn–Ag solder

The surface morphology, electrical property, solderability and interfacial reaction with Sn–3.5 wt.%Ag solder of two electroless nickel–boron (EN–B) deposits (Ni–1 wt.%B and Ni–3 wt.%B) were investigated. The B content of the EN–B layer decreased with increasing pH value. The crystallinity and solderability of the EN–B plating layer decreased with increasing B content, while the electrical resistivity increased. Reaction layers of Ni 3Sn 4 and Ni 3B were formed at the interfaces between the Sn–3.5Ag solder and the two EN–B deposit layers. The thickness of the interfacial Ni 3Sn 4 intermetallic compound (IMC) layer decreased with increasing B content, i.e., decreasing Ni content. These study results confirmed that the interfacial reaction between solder and the EN–B layer is significantly affected by the B content of the EN–B layer.