Electrical contact phenomena of nickel electrodeposits with sharp micro-asperities

The determination of the surface features that contribute to low contact resistance (R_c) values, especially after the coating is exposed to accelerated humidity testing, is addressed. Reflection electron micrographs showed that the nickel coatings with low R_c after humidity exposure have sharp asperities on the surface. The oxide layer of these surfaces was shown not to be tenacious since the film resistivity depends strongly on the contact force. These sharp micro-asperities appear to account for the low R_c behavior of gray coatings as they disrupt the insulating film on mechanical contact to create many small breaks in the oxide layer. Electrical contact then occurs through these breaks. At a load of 30 g or higher, the oxide is ruptured and the R_c is reduced to a low, stable value with or without exposure to an accelerated oxidizing environment