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

The Au-Sn alloy formed a Au-Ni-Sn intermetallic compound layer at the interface between the nickel underlayer and electroplated gold layer during thermal aging, thus preventing diffusion of the underlying nickel to the surface. This work broadens the visions for reducing gold usage and alternatives to conventional gold alloy contacting materials for electronic industries. [Display omitted] •Contact resistance and solderability of Au-Sn, Au-Co alloys were investigated.•The Au-Sn alloy exhibited lower a contact resistance and higher solderability than the Au-Co alloy.•Au-Sn-Ni intermetallic compound layer suppressed the diffusion of the underlying nickel. 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.