The pretreatment of aluminum bondpads for electroless nickel bumping

Electroless nickel bumping is a low cost approach to bumping. This method can also be used to convert the aluminum bondpad to a solderable surface (Ni/Au) for flip-chip application. In this study, Ni/P-bumps were produced by electroless nickel plating on different samples. For the pretreatment of aluminum bondpads, a commercial zincate solution was modified. The shear strength and the electrical resistance were investigated for different initial states of aluminum bondpads. It is shown that residues on the aluminum from the semiconductor fabrication can cause an increase in the electrical resistance and a decrease in shear strength. On clean aluminum bondpads, bumps with a shear strength of 180 cN and an electrical resistance below 1 mΩ have been achieved. Thermal cycling shows no significant decrease in the shear strength