Abstract
Silver plated films have been used as reflective films in LED reflectors because of their outstanding reflection properties for visible light. In this application, the formation of tarnish films on the silver surface is a serious problem. This tarnish is caused by the reaction of the silver films with trace amount of sulfur compounds in the atmosphere and by diffusion of copper from the underlying substrate.
In this paper, we report on the design of a novel multilayer plating system for the copper substrate, consisting of electrodeposition of palladium and nickel films as diffusion barrier layers, silver film as a reflective layer, followed by electrodeposition of ZnO film to prevent sulfuration. Formation of a dense ZnO film (90 nm) on the bright silver film is found to inhibit sulfuration of the silver film. The decrease in the reflectance of the silver film due to the diffusion of copper can be inhibited by the formation of protective palladium (0.1 μm) and nickel (1 μm) layers between the silver film and the copper substrate.
