Experiment study of dynamic looping process for thermosonic wire bonding

Looping is a complex dynamic process affected by many interacted factors, and is becoming more and more important in the state-of-the-art thermosonic wire bonding. To provide an insight view of loop mechanism, the looping process of standard loop was experimentally studied with a high resolution and high speed video camera. The capillary trace and loop profile evolution process were obtained from looping video with a digital image process program. A phenomenological description was used to understand the looping forming mechanism. The effect of capillary trace on loop profile was investigated, and the kinks forming mechanism were discussed. The spring back and kink up were detaily described. Experiment results show that loop profile was affected by kinks number, position on gold wire and deformation. Kinks were formed by reverse motion of capillary. From the geometry point of view, kink is the wire segment with the local maximum curvature. From the mechanical point of view, kink is the partly plastic deformed wire segment with elastic deformed core inside. This study may be useful for loop design in industry and for loop dynamic research in academic.