Manufacturing of Cu/electroless nickel/Sn-Pb flip chip solder bumps

A process for manufacturing Cu/electroless Ni/Sn-Pb solder bump is discussed in this paper. An attempt to replace zincation with a Cu film as an active layer for the electroless Ni (EN) deposition on Al electrode on Si wafer is presented. Cu/electroless Ni is applied as under bump metallurgy (UBM) for solder bump. The Cu film required repeated etches with nitric acid along with activation to achieve a satisfactory EN deposit. Fluxes incorporating rosin and succinic acid were investigated for wetting kinetics and reflow effectiveness of the electroplated solder bump. The solder plating current density and the reflow condition for achieving solder bumps with uniform bump height were described. The Cu/EN/Sn-Pb solder system was found to be successfully produced on Al terminal in this study that avoids using zincating process