Study on the Low-looped Ability of Forward and Reverse Looping Methods of Gold Wire Ball Bonding for Stacked Die Package Application

The packaging technology is driving to lower loop height level with the developments of multiple level stacked die packages and multi-tiered IC packages. It is very important to find moderate low-looped method to achieve perfect bondability and low-looped ability. The effects of looping methods on the bondability and low-looped ability were studied and analyzed. The study results shows that the low-looped ability of reverse looping is much better than that of forward looping due to the differences on the bonding mechanism and process between them; and SSB2 reverse looping can achieve very small low-looped height. For the forward looping, bonding quality is acceptable when looping height is higher than 110mum, but the cracks can be found on the neck zone of gold wire once the looping height is lower than 90mum. However, for the SSB2 reverse looping, after the optimizing selections on the reverse looping mode and capillary tip type, the looping height can be controlled from 60mum to 110mum effectively. Finally, the SSB2 reverse looping method optimized was applied in three-layer stacked die package, and the bonding quality and reliability are tested. The results show shows that the low-looped bonding ability of SSB2 reverse looping is completely acceptable, and the bonding process is stable and suitable for mass production