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Wire Bonding as Dynamic Process of Hardening and Softening

: Geißler, U.; Schneider-Ramelow, M.

Michel, B.; Lang, K.-D.:
Smart Systems Integration and Reliability. Honorary Volume on the Occasion of Herbert Reichl's 65th Birthday
Dresden: ddp Goldenbogen, 2010
ISBN: 978-3-932434-77-8
Aufsatz in Buch
Fraunhofer IZM ()

Ultrasonic wedge-wedge bonding of AlSi1 wires is characterised as a dynamic process of hardening and softening. The bonding parameters ultrasonic energy and bond force are acting in the opposite direction: While the bond force causes wire hardening ultrasonic energy causes softening and a better plasticity of the wedge. Increasing ultrasonic power is resulting in reduced wedge-hardness, i.e. the Aluminium wedge is more softened than using lower ultrasonic power. In the first phase of wire bonding the wedge is pre-deformed and cold worked by the bond force. After ultrasonic energy has been switched on, recrystallisation starts at the interface. During the bonding time hardening and softening processes alternate and a maximum in hardness is measured after 15 ms. 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 recrystallised and softer than the predeformated wedge, but harder than the as-received wire.