Significantly retarded interfacial reaction between an electroless Ni–W–P metallization and lead-free Sn–3.5Ag solder

To address the potential reliability challenges brought by the accelerated reaction with the adoption of lead-free solders, an electrolessly-plated Ni–W–P alloy (6–7 wt.% of P and 14–16 wt.% of W) was developed as the soldering metallization in this study. It was found that the electroless Ni–W–P layer was consumed much more slowly than the binary Ni–P layer after prolonged reaction. Unlike the Ni–P/Sn–3.5Ag interface where three intermetallic compounds (IMCs) are formed, only two IMCs are found at the Ni–W–P/Sn–3.5Ag interface. Besides, there is no void formation at the soldering reaction interface with the ternary metallization. The growth of Ni3Sn4 and (Ni, W)3P layers at the Ni–W–P/Sn–3.5Ag interface is found to be diffusion-controlled. The activation energies for the growth of Ni3Sn4 and (Ni, W)3P layers are 62.3 kJ/mol and 58.2 kJ/mol, respectively.

► A ternary Ni–W–P alloy has been plated as the metallization for lead-free soldering.
► The reaction mechanism and kinetics between the alloy and Sn–3.5Ag were studied.
► Two interfacial compounds are found at the reaction interface, and no voids are formed.
► The IMC growth kinetics are reported for both the Ni3Sn4 and (Ni, W)3P layers.
► The interface reaction is significantly slowed down compared with binary Ni–P alloy.