Characterization on ultra low loop Cu wire property and behavior

The heat affected zone (HAZ) is the major concern during wire loop formation. Wire looping is a process that involves machine mechanical movement as well as wire physical bending. Commonly, in order to avoid failure caused by mechanical stresses, most of the wire loop process setup will tend to avoid the HAZ. There are several factors contributing towards the length of HAZ. A study done by Sun et. al. explains that the increase of electron flame off (EFO) time is proportional towards the increase of HAZ length. Ultra low loop introduced an extreme bending process on top of the copper ball bond at the HAZ area. Wire necking or fracture is the major concern due to the effect of folding, bending and compression of the wire. The main focus of this paper will discuss on the detail and thorough characterization of ultra low loop, as low as 40-50um height in 22um copper wire in terms of process capability & robustness, material property & behavior (e.g.: grain structure) as well as the mechanical property (e.g.: hardness & strength). Common analytical method and material preparation setup error will be discussed and explained to understand the reasons behind in the data variations obtained.