Effect of EFO parameters and superimposed ultrasound on work hardening behavior of palladium coated copper wire in thermosonic ball bonding

Effects of the electrical flame off (EFO) and ultrasound (US) parameters on the work hardening behavior of Pd coated Cu (PCC) free air ball (FAB) are presented and compared to those of bare Cu reported in the literature. The FABs are characterized using an online deformability method that measures in situ deformed ball height (HDEF). The levels of EFO current (IEFO) of 65, 100 and 160mA with adjusted EFO time (tEFO) are used to make 40μm diameter FABs in two different shielding gases, resulting in six experimental conditions. In a first experiment, a total of 135 samples are produced for each condition and then deformed under a 400mN deformation force (FD) without superimposing US. PCC FABs produced in nitrogen gas using IEFO and tEFO of 160mA and 0.120ms, respectively, are more deformable, having HDEF 7.1–9.2% less compared to those produced with IEFO=100mA and tEFO=0.218ms. However, the FABs produced with the higher current vary more than those with lower current, and FABs produced with forming gas vary least. HDEF of PCC FABs made in forming gas is independent of IEFO in the range from 65 to 160mA. In a second experiment, the same conditions are used except for a 20% US level (equivalent to 29mW US power) superimposed on FD during the deformation. The values of HDEF with US is 5.7–11.7% and 6.5–9.0% smaller than those of without US for the IEFO ranging from 65 to 160mA in nitrogen and forming gas, respectively.