Electroless Ni-W-P alloy as a more enduring and reliable soldering metallization

The adoption of lead-free solders accelerates interfacial reaction because they have higher melting points and higher Sn content than the conventional Pb-Sn solders. In this work, we developed a ternary electroless Ni-W-P (6~7 wt.% P, and 15~16 wt.% W) alloy to be used as the soldering metallization due to its good thermal stability. Comparison was made with the results obtained from the conventional binary Ni-P (6~7 wt.% P) metallization. X-ray diffraction was used to study the crystallization behavior of the Ni-P and Ni-W-P deposits after annealing at various temperatures. The interfacial reactions at the Ni-P/Sn-3.5Ag interface and the Ni-W-P/Sn-3.5Ag interface were investigated after reflow and aging at 200 °C. While voids were found at the Ni-P/Sn-3.5Ag interface, which has been well known and explained, no voids were found at the Ni-W-P/Sn-3.5Ag interface after prolonged aging. In addition, it was found that the Ni-W-P layer was consumed much slower than the Ni-P layer, and the growth of Ni₃Sn₄ is much slower at the Ni-W-P/Sn-3.5Ag interface. These finding points out a promising lead-free solder metallization that is expected to enjoy improved reliability over long term aging and multiple reflow.