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 Hv 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.