The features of ultrasonic bonding interface were inspected by using a high resolution transmission electron microscope. Stress of ultrasonic bonding interface was analysed by the finite elements simulation. Results showed that the high stress of bonding interface was caused by ultrasonic vibration, which increased the dislocation density inside the metal crystalline lattice which provided the fast diffusion channels, and provided driving force for atom interdiffusion. 'Short-circuit diffusion' during ultrasonic bonding was more prominent than crystal diffusion. For the given ultrasonic bonding parameters, depth of atom diffusion at Au/Al interface of ultrasonic bonding was about 100 to 300nm in several tens of milliseconds, which forms the bonding strength of 0.65N, and it was an intermetallic compound of AuAl2.

Theoretical and Experimental Analyses of Atom Diffusion Characteristics on Wire Bonding Interfaces. J.Li, F.Wang, H.Lei, Z.Jue: Journal of Physics D, 2008, 41[13], 135303 (4pp)