EFFECTS OF PERIODIC REVERSE CURRENT ELECT ROLYSIS ON THE INTERNAL-STRESS IN NICKEL DEPOSITS

The variation in the average internal strain in the nickel deposit dur ing electrodeposition from a Watt type bath of pH=3.0 was successively studied using an electric resistance wire type strain gauge setup on the reverse side of a copper substrate having a preferred crystal orie ntation of the (200) plane. The influence of anodic current density du ring periodic reverse (PR) current electrolysis on the internal strain was also discussed. The internal strain cyclically changed from a ten sile one during the nickel deposition to its relaxation during the ano dic dissolution of part of the deposited nickel. On the other hand, an excessive anodic dissolution of the deposit caused the formation of a passive film on itself and resulted in a significant tensile strain i n the deposit. The nickel deposit with a preferred crystal orientation of the (200) plane always showed a tensile stress of smaller than 20 kgfmm(-2) for an average 8 mu m thickness. However, with an increase i n the orientation of the (220) plane, the tensile stress increased and vice versa for the (200) plane. The relatively small internal strain as compared to 7 kgfmm(-2) as the tensile stress in the deposit for an average 0.2 mm thickness was achieved under the PR current electrolys is conditions for the anode potential less noble than -0.1 V (vs. Ag/A gCl sat. KCl) and cathodic current of not more than the limiting curre nt density for the diffusion of nickel ions in the test solution.