Thermosonic soldering of cross-aligned strip solder bumps for easy alignment and low-temperature bonding

Abstract

In order to achieve easy alignment and low-temperature bonding for electronic packaging, cross-aligned strip solder bumps are thermosonically soldered using longitudinal vibration. The viscoplastic behavior and temperature distribution of the solder bump are calculated numerically, and the predicted results show good agreement with experimental results of fluxless thermosonic soldering of the lead-free solder (Sn-3%Ag-0.5%Cu). Melting of solder bumps occurs within 3 s with a perheating temperature of 85 degrees C, and growth of the intermetallic compound is limited due to the short bonding time. The effects of the bonding time and pressure on the bond quality are analyzed through SEM and bond strength measurement to determine the proper bonding condition of thermosonic soldering.