Characterization of Co-Sn intermetallic compounds in Sn-3.0Ag-0.5Cu-0.5Co lead-free solder alloy

The minor addition of Co into Sn-3.0Ag-0.5Cu lead-free solder alloy triggered the formation of Co-Sn intermetallic compounds. The Sn3.OAg-0.5Cu-0.5Co solder alloy was heated up to 300 degrees C or 400 degrees C and then cooled down to the room temperature at different rates. A new Co-Sn intermetallic phase, say, CoSn3 containing small amount of Cu, were detected. Only CoSn3 phase was formed in the solder alloy from 300 degrees C regardless of the cooling rate. However, during the solidification from 400 degrees C, the CoSn2+CoSn3 cascade structures were illustrated after slow furnace cooling due to the peritectical reaction, i.e., CoSn2 + L(Sn) -> CoSn3, while only CoSn2 was observed after rapid quench. A novel DSC technique was employed herein to demonstrate the presence of this peritectical reaction. The mechanical properties of the individual phases of Co-Sn intermetallics were measured and compared with other sole phases in the solder alloy. (c) 2007 Elsevier B.V. All rights reserved.