For connectors of electronic components installed in automobiles, Sn plating is used as surface treatment. Demand is increasing recently for reduction of connector insertion force and for improvement of connection reliability in high-temperature environments. To meet those demands, various processes using Sn-based intermetallic compounds have been developed as alternative surface treatments for Sn plating. Needs for automotive connectors are expected to continue their expansion. Therefore, we investigated a Sn-Cu plating process able to provide more stable characteristics. After stacking Sn-Cu plating and Sn plating, thermal treatment was used to form intermetallic compounds. Just below the surface, Cu6 Sn5 intermetallic compound layers with low roughness are formed. A pure Sn layer is then formed on it. Forming a pure Sn layer with high connection reliability and an intermetallic compound layer with high hardness in a stable state can be expected to improve various characteristics. Evaluation of the friction coefficients and the contact resistance obtained using the investigated process revealed that good characteristics were obtained.