Lead free solder materials In-Sn-Zn system

We investigated the bulk as well as surface properties of the In-Sn-Zn system because of its potential as lead free solder materials. Differential thermal analysis X-ray and microprobe analysis were performed on forty ternary samples. Our X-ray investigation showed a single phase at 10 and 25 at.% Zn and two phases (gamma + Zn) at 40 and 55 at.% Zn. Quenched samples showed an invariant effect in gamma + [Zn] solid solution. Heat treatment did not produce any effect on the ternary eutectic temperature. A statistical mechanical theory based on a layered structure has been used to develop expressions for the surface tension (gamma) and surface composition (C-s) in the frame-work of self-association and compound formation models. These expressions have been utilised to compute gamma and C-s of In-Sn and Sn-Zn systems as a function of concentration and temperature. Our study suggests an increase in gamma of both (In-Sn and Sn-Zn) systems with the addition of In to Sn and Zn to Sn, respectively. It is interesting to observe that Sn atoms segregate to the surface of both the systems at all bulk compositions - with the larger extent of segregation in Sn-Zn. Segregation of Sn atoms and formation of di-atomic like atoms clusters (Sn-2) might be influencing the wetting and adhesion in solder joints. (C) 1999 Elsevier Science B.V. All rights reserved.