Improved reliability of Sn-Ag-Cu-In solder alloy by the addition of minor elements

Among the various Pb-free solder alloys, Sn-3.0Ag-0.5Cu has been an industrial standard in consumer electronics due to its moderate wetting behavior and reliability in thermal fatigue. Recently, however, its high material cost and low reliability in drop impact condition resulted in the use of Sn-0.3Ag-0.7Cu and the development of Sn-1.2Ag-0.7Cu-0.4In solder alloys. Authors have reported that the Sn-1.2Ag-0.7Cu-0.4In showed as good wettability as Sn-3.0Ag-0.5Cu and load drop reliability as Sn-1.0Ag-0.5Cu. It was believed that the small addition of In could make up for the large reduction of Ag with the material cost benefit of about 20%. It was also noteworthy that the load drop reliability of Sn-1.2Ag-0.7Cu-0.4In could be improved beyond Sn-1.0Ag-0.5Cu by the small addition of some elements. In this study, effects of the minor elements, on the reaction, mechanical properties and reliability were investigated.