Lead-tin solders have been the most prominent materials for the interconnection and packaging of modern electronic components and devices during the past several decades. However, in view of environmental and health concerns, the Sn-base Pb-free solder alloys are needed as candidates for replacement of widely used Pb-Sn solders.
Properties of many alloy systems are generally governed by their microstructures composed of various phases. When these phases are in equilibria, they can be expected from phase diagrams. In view of this, a thermodynamic study on the phase equilibria has been undertaken to characterize and then design the Sn-In-Bi system which is one of appropriate candidates for Pb-free solder alloys and low-temperature applications.
As a part of ongoing program on alloy designs of Pb-free solders systems, thermodynamic reassessment of Bi-Sn system and assessment of Sn-In system have been performed.
Thermodynamic information on these binary systems was used to extend to the calculation of Sn-In-Bi ternary system through Muggianu model. And in order to express the experimental data preciously, ternary correction terms were adopted.
XRD, SEM, EDX analysis have been carried out for the sake of confirming the identification of phases on the Sn-In-Bi ternary system. And calculated phase diagrams of this ternary system are compared with DSC measurements along several vertical sections of the ternary.
As results of this study, many experimental data have been agreed with the thermodynamic calculation using a Thermo-Calc program.
