High Frequency and Low Temperature Thermosonic Bonding of Lead Free Microsolder Ball on Silver Pad Without Flux

Abstract

Leadfree solder balls are environment friendly; however, they require a high bonding temperature, which causes problems in the microelectronics package industry. To reduce the bonding temperature, a 60 kHz highfrequency thermosonic bonding method is proposed and realized using a lab bonder. Experimental results showed that this method could be used to bond a 300 خ¼mdiameter Sn–Ag–0.5Cu microsolder ball onto a silver pad without flux at a low temperature of 160 آ°C in 3 s. A ball shear test showed that the high frequency led to a high bonding strength of 58.8 MPa, and a dimpled structure was observed at the bonding interface by SEM. Compare with the reflow method or laser soldering method, the proposed method requires a low bonding temperature and leads to a high bonding strength.