Study of free air ball formation in Ag–8Au–3Pd alloy wire bonding

• The EFO current was the key factor to influence the Ag–8Au–3Pd alloy FAB size and morphology.
• Mechanisms of FAB defects including off-center and ripple formation were discussed by solidification process.
• A medium flow rate was suitable for Ag–8Au–3Pd alloy FAB formation.
• Under the protection of shielding gas, oxidation and sulfuration of the Ag–8Au–3Pd alloy FAB were effectively prevented.

An innovative Ag–8Au–3Pd alloy wire has been developed as an alternative to the traditional gold wire bonding. This paper focused on the free air ball (FAB) formation of 0.7 mil Ag–8Au–3Pd alloy wire, which was vital for the yield of the subsequent bonding process. During electric flame-off (EFO) process, the wire tail was melted by a high voltage spark, and then the FAB was shaped by the effects of surface tension and gravity. The EFO current was the key factor to influence the Ag–8Au–3Pd alloy FAB size and morphology due to the energy input via arc discharging. The defects including off-center and ripple appeared on the Ag–8Au–3Pd alloy FABs were discussed by cooling and solidification. It is suggested that low EFO current will effectively avoid FAB defects. The contaminants on the Ag–8Au–3Pd alloy FAB surface were analyzed by Auger electron spectroscopy (AES). Under the protection of the shielding gas, oxidation and sulfuration have been effectively prevented.