The contact resistances of multilayered Sn/Ag electroplating with a 50 nm-thick Ag-Sn alloy film as Ag3Sn nano-flakes in 50-200 nm across on copper alloys were investigated after aging at ambient temperatures of 150, 175, and 200 °C for 120 h to 3000 h in air. The microstructures and surface characteristics of the Sn/Ag coatings after aging at different temperatures and periods were elaborated using SEM, FE-SEM, XRD, TEM, GDOES, and AES. The Sn/Ag coatings exhibited low and stable contact resistances equivalent to that of as-plated sample even after aging at 200 °C for 3000 h, compared to the ever-increasing contact resistances for conventional reflowed Sn coatings without Ag plating, especially at the low-load side. The excellent stability of the contact resistance of the multilayered Sn/Ag coatings can be ascribed mainly to Ag3Sn microparticles that are agglutinated on the coating surfaces, and to their good oxidizing resistance, irrespective of the oxidation of Cu-Sn alloys during aging. Moreover, the oxide films on the Sn/Ag coatings after aging were much thinner than those on the reflowed Sn coatings. In particular, a tiny amount of Ag was included the Cu-Sn intermetallic compounds and agglutinated at the Cu3Sn/Cu interface with aging. This phenomenon can be attributed to the inward Ag diffusion countered against the outward Cu diffusion from the base materials, which enhanced the anti-oxidation and adhesion characteristics of the coatings, thus leading to a high reliability under high-temperature circumstance for electrical devices in automotive applications.
Diamond-like carbon (DLC) films, which have excellent mechanical and tribological properties, have been used for many applications such as magnetic hard disks, dies, gears, cutting tools, and other moving mechanical assemblies. Because those applications center upon mechanical engineering parts, tribological studies of DLC have mainly examined their performance against metal surfaces. This study investigated the friction properties of DLC films against non-metallic materials such as wood, cloth, and paper. Using direct current plasma enhanced chemical vapor deposition (DC PECVD) technique with tetramethylsilane (TMS) and benzene, DLC film was deposited onto a steel substrate. For the wood surface, the friction coefficient was measured with different moisture contents of wood. Results show that the friction coefficient was lower using DLC coated steel than when using non-coated steel. For wood with high moisture, the DLC treatment increased the friction coefficient.