Thermodynamics-aided alloy design and evaluation of Pb-free solder, Sn-Bi-In-Zn system

Abstract

To design Pb-free solder alloys which are drop-in replacements for 63Sn-37Pb (compositions are all in weight percent, otherwise specified), thermodynamic studies on the Sn-Bi-In-Zn quaternary system were carried out in terms of phase equilibria. Based on the results of phase equilibria calculations, several specific alloy compositions were selected and analyzed using differential scanning calorimetry (DSC) measurements. DSC results were compared with thermodynamically calculated phase transition and melting temperatures. Liquidus temperatures were slightly higher than 200 degrees C, however, solidus temperatures were lower, in the range of 130 degrees C-180 degrees C. Microstructures of as-cast and heat-treated alloys were examined through scanning electron microscopy (SEM) and X-ray diffraction (XRD) analyses. Welting tests were also performed at 240 degrees C to investigate the interfacial reaction between the Cu substrate and solder alloys. The Cu5Zn8 intermetallic phase was found at the interface instead of the Cu6Sn5 or Cu3Sn in phases that are normally observed in Sn-base solder alloys. Copyright (C) 1997 Acta Metallurgica Inc.