Development of Cu-Sn intermetallic compound at Pb-free solder/Cu joint interface

The development of Cu-Sn intermetallic compound (IMC) at the solder/Cu joint interface had been studied using two Pb-free solders, Sn-3.8Ag-0.7Cu and Sn-2Ag-0.8Cu-0.6Sb alloys. Meanwhile, 100Sn/Cu joint was applied for comparison. Both Pb-free solder joints were found with thinner Cu-Sn IMC layers at as-soldered state due to the slower dissolution rate of intermetallic compound into the liquid Pb-free solders during reflow and, consequently, slower growth rates of Cu-Sn IMC during the solid-state thermal aging at 125 degreesC, where Sn-2Ag-0.8Cu-0.6Sb solder joint gave the minimum value. Thermodynamic analysis showed that such phenomena could be attributed to the reduction of the driving force for Cu-Sn IMC formation due to the existence of Ag and Sb atoms. (C) 2003 Elsevier Science B.V. All rights reserved.