Solder bump formation using electroless plating and ultrasonic soldering

Aluminum electrodes in the Si wafer were surface-treated in the sequence palladium activation, Ni-P electroless plating, ultrasonic soldering with Pb-1Sn solder, and dipping in Sn-37Pb to form second-stage solder bumps. The average bump height and the shear force were 20.3 mu m and 26.8 g/pad, respectively. The shear force did not decrease after the heating test (150 degrees C*1000 h) or thermal cycle test (-65 degrees C (--) room temperature (--) 150 degrees C, 300 cycles). Aluminum diffused to amorphous Ni-P through the Pd layer, Ni-Sn intermetallic compounds were formed at the Pb-1 Sn/Ni-P interface. The low-cost polyester tape-automated bonding was utilized to melt low temperature second solder on inner lead bonding. No bridge occurred when applying this technique to an LSI device with 376 electrodes, 100 mu m wide with 150 mu m pitch.<>