Oxide development on coated copper contacts

Corrosion of components within electronic systems can produce a wide range of consequences from intermittent electrical faults to complete functional breakdown. Temperature and relative humidity are key environmental parameters, which control corrosion. This paper presents an investigation of copper contacts plated with gold, palladium-nickel and nickel exposed to steady-state damp heat conditions. Studies were conducted to evaluate the oxide development on the contacts after steady-state exposure using scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDAX), focused ion beam (FIB), and secondary ion mass spectroscopy (SIMS). The diffusion of copper to the gold surface is the rate-limiting step in the corrosion process and the nickel layer acts as a diffusion barrier. It is shown, however, that the nickel layer retards - but does not prevents diffusion. The oxide development on the gold surface is shown to increase slightly with increasing relative humidity with a critical relative humidity shown to above 90%RH.