Hardening and Softening in AlSi1 Bond Contacts During Ultrasonic Wire Bonding

Ultrasonic wedge-wedge bonding of 25-mu m AlSi1 wires is characterized as a dynamic process of hardening and softening. In the first phase of wire bonding, the wedge is predeformed and cold worked by the bondforce. After ultrasonic energy has been switched on, recrystallization starts at the interface. During the bonding time hardening and softening processes alternate and a maximum in hardness is measured. Hardening and softening processes correlate well with the grain structure, the measured grain sizes and a typical plateau in the z-deformation curve of the contact. At the end of the wire bonding process the wedge is recrystallized and softer than the predeformated wedge, but harder than the as-received wire.