The effect of the nickel underplate on the heat resisting properties of silver plated copper alloy contacts

Heat resisting properties of Ag plated copper alloy contacts with Ni underplate were investigated by electron backscatter diffraction (EBSD), scanning transmission electron microscope (STEM), X-ray photoelectron spectroscopy (XPS) and contact resistance measurements. Ni underplate effectively prevented copper diffusion to the Ag surface from the substrate during 200°C heating, and the prevention effect saturated in 0.25 μm or more of the thickness. Ni was not detected in the Ag surface after heating at 200°C for 500 h. From the observation with STEM, it was found that Cu mainly diffused through grain boundaries of Ni and to the Ag surface. Decreasing the density of grain boundaries in Ni is possible to prevent diffusion of Cu, even the thickness of the Ni underplate is 0.1 μm.