Electrical contacts on nickel plated aluminium: the state of the art

A direct nickel plating procedure for aluminum is described. It is shown that the main disadvantage of aluminum as far as electrical applications are concerned, namely its unstable contact properties, can be cured by direct nickel plating. This economical solution meets all standards, including the highly demanding standards of the airplane industries. Untreated aluminum surfaces and coated aluminium are considered. Instead of the several steps imposed by the standard procedures, the procedure requires only two basic steps: surface activation and electroplating. The electrolytes are selected so as to warrant pure nickel layers free of residual internal stresses. The method (developed for wires) through liquid contacts allows high current densities, thereby a rapid plating (typically 1 μm/s) and a high yield. The nickel layer obtained with this procedure is globular, with nodules about 0.5 μm in diameter, which favors better electrical contacts. The improved properties brought by recent developments of this technology are discussed, and the severe certification tests performed for use on airplanes are reported. In particular, the test conditions were: 500 heat cycles, tang current densities in the vicinity of 150 A/cm², (up to 250 A/cm²), connector lug temperature up to 165°C, and cable temperature near 210°C