Investigation of Complex Looping Process for Thermosonic Wire Bonding

Wire looping is a critical part of a modern wire bonder. A major concern in wire bonding is the loop profile and loop height consistency, particularly for complex loops with more than four kinks for 3-D packages. To understand the effects of various parameters on complex loop profiles, a 3-D finite element (FE) model is developed with LSDYNA. Experiments observation of the looping process is carried out using high speed camera to verify the FE model. This FE model is used for investigating the effect of material properties, wire tension force, and clamp action on loop profile. Experimental and simulation results show that a complex capillary trace is used for a complex loop, and six kinks are formed. The loop profile is mainly determined by the number of kinks, kink position and deformation. The upward stage of capillary trace is mainly used for forming kinks and shape the loop profile, the downward stage only slightly changes the loop profile. Larger tension force, open clamp, softer materials, and larger reverse motion parameter can reduce the loop height. A constant wire tension force and precise clamp action can improve the loop consistency.