Effect of the addition of In on the microstructural formation of Sn-Ag-Zn lead-free solder

The effect of addition of In, up to 1 wt.%, on the formation of intermetallic compounds (IMCs) in the solidified Sn-3.7%Ag-0.9%Zn lead-free solder was investigated. As observed by microstructural analysis, the typical structure of Sn-Ag-Zn solder is composed of beta-Sn phase and mixed granules of Ag3Sn and AgZn IMCs. After alloying with In, it evolves into a mixture of randomly distributed rods and granules of AG(3)Sn and AgZn. Clearly, the addition of In into the explored Sn-Ag-Zn solder promotes the formation of rod-like IMCs for the reason that the growth competition of the Ag3Sn and AgZn IMCs was destroyed by the selective adsorption of In atoms on a certain preferable crystalline planes of the separated IMCs. The change in the morphology of the formed IMCs leads to a great difference in the mechanical performances, for example, the measured microhardness of the investigated solders evolves from 16.95 HV to 21.35 HV with the increase of In content. (C) 2007 Elsevier B.V. All rights reserved.