Effect Of In On Mechanical Properties Of Low Silver SnAgCu Solder And Reliability Of Soldered Joint

With the development of lead-free solder process in electronic packaging, Sn-Ag-Cu alloys with good wettability, mechanical properties and reliability are the most potential alloys to alternate Sn-Pb solder. However, high melting point and Cu6Sn5 coarsen when isothermal aging limited the popularity of Sn-Ag-Cu alloys in electronic packaging. In addition, the high price of Ag also reduces its utilization. Therefore, the study of low silver Sn-Ag-Cu and improve its performance has extremely significance.In this study, we compared the microstructure and mechanical properties of Sn-Ag-Cu solder with different Ag content. The feasibility of Sn-1.0Ag-0.5Cu alternate high silver SnAg-Cu solder was discussed. Then, In element was doped into Sn-1.0Ag-0.5Cu to investigate its microstructure, melt point, wettability, the growth of intermetallic compounds and joint reliability. The transformation of tensile strength and shear strength during isothermal aging was investigated. The results indicated that the wettability increased with Ag content increase, and the net-work eutectic also increased. The size of IMC in Sn-Ag-Cu/Cu interface was smaller when Ag content increased. The shear strength of BGA solder joints was decrease and then tended towards stability after isothermal aging. The shear strength of Sn-1.0Ag-0.5Cu and Sn-3.0Ag-0.5Cu was almost equal after 960 h aging at 150?. It indicated that after long time serving at high temperature, Sn-1.0Ag-0.5Cu could alternate Sn-3.0Ag-0.5Cu due to its stability during isothermal aging.Melt point decreased with In increased in Sn-1.0Ag-0.5Cu-x In after In element addition. Sn-1.0Ag-0.5Cu-4.0In has the maximum spread areas, but In deteriorates its oxidative stability. The microstructure of Sn-1.0Ag-0.5Cu was refined due to In addition. When In content beyond 2.0%, bulked IMC appeared in the Sn-1.0Ag-0.5Cu-x In matrix. The morphology and thickness of IMC at Sn-1.0Ag-0.5Cu-x In/Cu interface was almost the same. In element participated the formation of IMC which was Cu6(Sn,In)5. During isothermal aging, the thickness of IMC increased gradually, In addition inhibited the IMC transformation from Cu6(Sn,In)5 to Cu3(Sn,In) obviously when In addition was 2.0%. In element improved the ultimate tensile strength and ultimate shear strength of Sn-1.0Ag-0.5Cu-xIn solder joints at the same time. During isothermal aging, the tensile strength and shear strength of BGA solder joints was decrease and then tended towards stability after isothermal aging. Sn-1.0Ag-0.5Cu-2.0In has the highest performance after aging 960 h. Combined with costing, the mount of In element addition should not be more than 2.0%.