Properties of Sn-Ag-Cu-In Quaternary Lead-free Solder Alloys with In Content

초록

During the past decade, Sn-3.0~4.0(wt.%)Ag-0.5~1.0Cu Pb-free alloys have been used as a common solder material in the electronic industry as replacements for Pb-based compositions. However, an increase in the number of Pb-free alloy choices has been seen recently in electronic packaging research, including Sn-Ag-Cu alloys with low Ag (less than 2.5wt.%) content, due to concerns on the high raw material cost of alloys, poor drop/shock performance, and so on. However, low Ag solder alloys show relatively inferior wettability and mechanical strength to near-eutectic Sn-Ag-Cu alloys. The wettability and mechanical strength of low Ag alloys could be enhanced with alloying additive additions, but the addition content should be minimized to preserve the essentially excellent mechanical properties of Sn-Ag-Cu alloys. In this study, we chose In (indium) to be added into the Sn-1.2Ag-0.5Cu alloy. Because In (indium) is more costly than Ag, it was not given the spotlight for industrial soldering uses but if the added amount is small enough, it can be economically viable for industrial use. Therefore in this study, we will add less than 1wt.% In (indium) to the Sn-1.2Ag-Cu alloy and we will study the effects of the solder’s wettability, melting, solidification properties, mechanical properties and interfacial reaction properties. In the procedure of minimizing the amount of Ag in Pb-free solder alloy, the addition of small amount of In element significantly improves the wettability and mechanical properties of the alloy. With these results, we could suggest that Sn-Ag-Cu-In quaternary alloy such as Sn-1.2Ag-0.5Cu-0.4In would be a strong candidate for the replacement of Sn-3.0Ag-0.5Cu composition.