Activation of copper surfaces in chemical deposition of composite nickel coatings

Electroless nickel plating of copper surfaces has perspective application both in electronics (for deposition of the final two layered NiP/Au coating on contact copper spots of printing circuit cards) and in microtechnique (for preparation of microstructures). Copper and its alloys do not exert any catalytic effect on the main redox reaction running in electrolytes for electroless nickel plating and therefore their preliminary activation is required. The present paper summarises the experimental results obtained with activation of copper surfaces using solutions containing palladium ions and a complexant. The optimum concentration of the activating solutions and operation conditions are established, providing uniform NiP coatings of sufficient thickness and good morphology. A special attention is paid to the deposition of composite NiP-TiO2 coatings. The electroless nickel plating is performed in electrolytes comprising NiSO4.7H(2)O, NaH2PO2.H2O, complex forming and buffering substances, stabilisers and dispersoid (.)- TiO2. The size of the dispersoid particles is between 30 and 60 nm. The activation conditions are established under which a maximum deposition rate has been recorded and the microhardness of produced composite coating is 30% higher than that of conventional NiP coatings.