A thermodynamic and experimental determination of the copper-indium-lead ternary phase diagram

The C-4 microelectronic interconnection technology is briefly reviewed, and the inherent advantages of using lead-indium solder in this packaging scheme are considered. A case is then made for evaluating the Cu-In-Pb ternary phase diagram, based on the prevalence of copper in current packaging technology and a lack of satisfactory data on the metallurgical interactions between copper and lead-indium. The literature pertaining to the constituent binary diagrams in this system is reviewed, with determinations made on the validity of some temperature-composition and thermodynamic values. This data is then used to calculate these same binary phase diagrams, and the parameters within describing the excess Gibbs excess free energy of the phases are extrapolated to determine the first order Cu-In-Pb ternary phase diagram. The first order model provides a reasonable estimate of the topology and serves as a guide to efficient experimentation. Predicted isothermal and isoplethal sections, as well as invariant reaction temperatures, are compared with those determined by experimental methods, namely DSC/DTA and EPMA. The experimental results indicate where adjustment to the thermodynamic parameters is necessary. Optimization of these parameters is achieved by inserting the relevant experimental data into a least-squares calculation, so that the discrepancy between calculated and experimental values are minimized. The final phase diagram, recalculated with the optimized parameters, is once again compared with the experimental data to verify that it more closely reflects the phase equilibria proposed by the experimental investigation. Finally, uses in microelectronics packaging and diffusion studies for the various calculated sections and liquidus projections of the Cu-In-Pb phase diagram are presented.