Homogeneous Cu6Sn5 and Cu3Sn joints were formed in Cu/Sn foil/Cu interconnection system respectively, using ultrasonic bonding process for a short period of 3 seconds at room temperature. This ultrarapid development of full intermetallic compound (IMC) joints required an accelerated interdiffusion kinetics at the interface between liquid Sn and solid Cu which could be wholly attributed to the sonochemical effects induced by acoustic cavitation phenomenon. When bubble collapsed near the liquid/solid interface, excessive cavitation erosion was generated on the solid Cu surface, resulting in supersaturation of Cu in the liquid Sn and hence facilitating the formation of intermetallic phases as chemical reaction products. The resulted intermetallic joints performed high mechanical reliability.