The adhesion between electroless nickel deposit and Si/Al/Cu bump pad

The adhesion strength of Si/Al/Cu/EN(electroless nickel) multilayer structure has been investigated by pull test as well as by shear test. Electroless nickel deposit lowers the pull strength of Al/Cu deposit on Si from 4.8 kpsi to 3.0 kpsi. The electroless nickel was deposited by a continuous and an intermittent deposition process. The intermittent deposition process will enhance the shear strength of the electroless nickel bump, a shear strength of 60 g/bump was achieved for a bump diameter of 60 µm. Thermal cycling test degrades the pull strength of the deposit from 3 kpsi to 2 kpsi, while it lowers the shear strengh of an electroless nickel bump from 60 g/bump to around 30 g/bump. Fracture mechanism was investigated by analyzing the fracture surface of the structure. It was found that the fracture mechanisms are different for these two adhesion test methods.