Improved contact resistance and solderability of electrodeposited Au-Sn alloy layer with high thermal stability for electronic contacts

We investigated the effect of thermal aging on the contact resistance and solderability of Au-Sn and Au-Co alloy films. The Au-Sn alloy exhibited lower contact resistance and better solderability compared to the conventional Au-Co alloy. In the Au-Sn alloy, an Au-Sn–Ni intermetallic compound layer was formed at the interface between the electroplated Ni and Au-Sn layers during the thermal aging process. The resulting Au-Sn–Ni layer effectively blocked the diffusion of underlying nickel to the surface, leading to improved solderability and enhanced thermal stability of the contact resistance. Meanwhile, the results revealed that a significant amount of nickel diffused to the surface of the Au-Co alloy during the thermal treatment, and the nickel atoms on the surface were oxidized to NiO or Ni₂O₃, which increased the contact resistance and deteriorated solderability by acting as a barrier layer.