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 Ni3Sn4 and Ni3B were formed at the interfaces between the Sn–3.5Ag solder and the two EN–B deposit layers. The thickness of the interfacial Ni3Sn4 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.