Fabrication and adhesion of low stress electroless Ni-Cu-P bump on copper pad

The addition of copper into electroless Ni-P deposits will improve the thermal stability and the solderability of the deposits. However, it also results in excess tensile stresses of the deposits. In this study, a nearly stress-free amorphous electroless Ni-Cu-P deposit (Ni-15Cu-12P) on copper is produced when one adds 10 g/l saccharin in the Ni-Cu-P solution. The addition of saccharin inhibits the coalescence of electroless Ni-Cu-P nodules and thus decrease the tensile stress of the deposit. Furthermore, electroless Ni-Cu-P bumps can be selectively deposited on Si/Ti/Cu pads by using dimethylamine borane (DMAB) as activators. The shear strength of the Cu/Ni-Cu-P bumps (100 μm×100 μm area and 10 μm height) on silicon wafer is above 100 g, and the fracture occurs at the Ti/Cu interface.