A new technique of direct solder bump formation on an Al pad for flip-chip interconnection was developed by using a rapidly solidified Sn-1Ag-1Zn-5Sb alloy wire. The solder balls made from the wire by arc discharge in Ar containing H2 were bonded to an Al-1Si layer by thermosonic bonding at 423 K in air. The addition of Zn and Sb into the Sn-base alloy was effective in obtaining a good contact state between the ball and the Al-1Si layer. The shear strength of the Sn-base alloy bump is 61 MPa in the as-bonded state and remains almost unchanged even after aging for 400 h at 473 K. The fracture morphology also remains unchanged upon aging. Furthermore, there is no distinct increase in the interdiffusion distance between Sn and Al. These results allow us to expect practical use of the direct solder bump formation technique on Al pad with high reliability.