SOLDER BUMP FORMATION USING ELECTROLESS PLATING AND ULTRASONIC SOLDERING

Aluminium electrodes in the Si wafer were surface-treated, in the sequence involving 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 µm and 26.8 g/pad, respectively. The shear force did not decrease after the heating test (150°C × 1000 h) or thermal cycle test (−65°C ↔ room temperature ↔ 150°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 TAB was utilized to melt low-temperature second solder on inner lead bonding. No bridge occurred when applying this work to an LSI with 376 electrodes, 100 µ m wide with 150-µm pitch. © 1990 IEEE.