Experimental verifications of the Sn-In and Sn-In-Ag phase equilibria have been conducted. The experimental measurements of phase equilibria and thermodynamic properties are used for thermodynamic modeling by the CALPHAD approach. The calculated results are in good agreement with experimental results. Interfacial reactions in the Sn-In-(Ag)/Ag couples have been examined. Both Ag(2)In and AgIn(2) phases are formed in the Sn-51.0 wt%In/Ag couples reacted at 100 and 150 degrees C, and only the Ag(2)In phase is formed when reacted at 25,50 and 75 degrees C. Due to the different growth rates of different reaction phases, the reaction layer at 100 degrees C is thinner than those at 25 degrees C, 50 degrees C, and 75 degrees C. In the Sn-20.0 wt%In/Ag couples, the zeta phase is formed at 250 degrees C and zeta/AgIn(2) phases are formed at 125 degrees C. Compared with the Sn-20 wt%In/Ag couples, faster interfacial reactions are observed in the Sn-20.0 wt%In-2.8 wt%Ag/Ag couples, and minor Ag addition to Sn-20 wt%In solder increases the growth rates of the reaction phases. (C) 2011 Elsevier B.V. All rights reserved.