Pulse Electroplating of Ni-W Alloy for the Diffusion Barrier in Under Bump Metallurgy

Ni-W alloy was electroplated from citrate bath. The crack-free coatings were obtained using the pulse electroplating method. The surface hardness was increased up to 700 H_v and it is twice as high than that of the electroplated Ni. The surface hardness was increased as the content of W in the coating increased. However, the higher W contents made surface cracks and the surface hardness was decreased. Ni-W alloy made less intermetallic components (IMC) and the shear force of solder ball was increased as much as 20% compared with conventional Ni plating.