High temperature lead-free solder for microelectronics

This paper reports results of a four-year industrial consortium effort to d evelop lead-free solders for high-temperature applications (up to 160 degre esC). Work included preliminary evaluations of 32 tin-based alloys, a scree ning of the thermomechanical fatigue performance of 13 promising alloys, an d a full manufacturability and fatigue testing of the seven most promising of those alloys, namely Sn-3.5Ag, Sn-4Ag-1Cu, Sn-4Ag 0.5Cu, Sn-2.5Ag-0.8Cu- 0.5Sb, Sn-4.6Ag-1.6Cu-1Sb-1Bi, Sn-3.3Ag-1Cu-3.3Bi, and Sn-3.5Ag-1.5In (comp ositions in weight percent). Eight different components were used on the re liability test vehicle, and the alloys were compared through Weibull analys is. In addition, the same seven experimental alloys were tested with ball g rid army packages cycled up to 100 degreesC or 125 degreesC. All the lead-f ree alloys performed well, but those containing bismuth showed especially o utstanding performance. In general, the ternary and higher alloys performed as well or better than the indus try standard tin-silver eutectic, suggest ing that solders other than the tin-silver eutectic should be considered fo r high-reliability, high-temperature applications.