Fabrication of nickel microbump on aluminum using electroless nickel plating

Fabrication of nickel microbumps on an aluminum electrode using a nickel displacement and a direct nickel plating process was investigated. Electroless nickel plating reaction with hypophosphite as a reducing agent was not initiated on the aluminum substrate, because aluminum does not have catalytic action on the oxidation of hypophosphite. Accordingly, nickel was initially deposited on the aluminum using nickel displacement plating for the initiation of the electroless plating. Nickel bumps on the aluminum electrode were fabricated by treatment of the nickel displacement plating followed by electroless nickel plating. Nickel microbumps also can be formed on the aluminum electrode without the displacement plating process. Activation of the aluminum surface is an indispensable process to initiate electroless nickel plating. Uniform bumps 20 mu m wide and 15 mu m high with good configuration were obtained by direct nickel plating after being activated with dimethyl amine borane.