A corrosion couple experiment reproducing the black pad phenomenon found after the electroless nickel immersion gold process

The “black pad” phenomenon, which rarely occurs in electrolessly plated nickel–phosphorous (Ni–P) films, was reproduced. This work reports that nodular variation of the P content induces potential differences large enough to drive galvanic corrosion when the film is exposed to an electrolyte containing gold cyanide. Subsequent corrosion couple experiments using Ni–P films with different P contents demonstrated that preferential corrosion occurred at the low P side, and the propensity of forming black pad increased with the difference in P content (ΔP).