Cyanide-free silver electroplating was conducted in thiosulfate baths containing AgNO3 and AgBr major salts, respectively. The effects of major salt content and current density on surface quality, deposition rate and microhardness of Ag coatings were investigated. The optimized electroplating parameters were established. The adhesion strength of Ag coating on Cu substrate was evaluated and the grain size of Ag coating was measured under optimized electroplating parameters. The optimized AgNO3 content is 40 g/L with current density of 0.25 A/dm2. The deposited bright, smooth, and well adhered Ag coating had nanocrystalline grains with mean size of 35 nm. The optimized AgBr content was 30 g/L with current density of 0.20 A/dm2. The resultant Ag coating had nanocrystalline grains with mean size of 55 nm. Compared with the bath containing AgBr main salt, the bath containing AgNO3 main salt had a wider current density range, and corresponding Ag coating had a higher microhardness and a smaller grain size.
Cu films on Fe, Ni and Ag substrates, Ni films on Fe and Ag substrates, Ag film on Cu substrate, Cr film on Fe substrate, Ag film on Ag substrate, Ni film on Ni substrate and Cu film on Cu substrate were deposited by electroplating. The average internal stress in all films, except Cr, was in-situ measured by the cantilever beam test. The interfacial stress is very large in the films with different materials with substrates and is zero in the films with the same material with substrates. The interfacial stress character obtained from the cantilever beam bending direction is consistent with that obtained from the modified Thomas–Fermi–Dirac electron theory.
