Improved uniformity of Ni/Au coating on circuits by electroless plating

Abstract

Cyanide-free electroless plating was used to deposit nickel/gold coating on the patterned circuits with fine-pitch. The relationship among the controlled process parameters, the skip plating, over-plating and pit forming were investigated. Results show that due to the uniform discharge sputtering, the copper layer is failed to be deposited around BVHs and lines of Al₂O₃ samples. The skip plating is mainly caused by the self-oxide and the leakage sputtering with copper. Excess Pd activation may result in over-plating during plating nickel. With enhancing the uniformity of the substrate materials and raising the annealing temperature, the number of pits decreases significantly. The thickness of the Au coating can reach up to 2 µm with the smooth coating surface and without the spillover. The electroless plating Au progress can be used to fine-pitch selective area plating.