The effect of Pb contamination on the solidification behavior of Sn-Bi solders

This paper presents experimental results and theoretical calculations to ev aluate the effects of Pb contamination on the solidification behavior of Sn - x Bi alloys (x = 5, 10, and 58 mass %). The pasty (mushy) range, the typ e of solidification path, and the fraction of the ternary eutectic are desc ribed. The experimental results are obtained from thermal analysis and quan titative metallography, and the solidification calculations are performed u sing Lever and Scheil assumptions. The experimental, results agree with the Scheil calculations. The freezing range of Pb contaminated Sn-Bi solders i s greatly increased due to the formation of a ternary eutectic reaction at (95.3 +/- 0.5)degrees C. This increase is a likely cause of porosity in con taminated solder joints. The results provide an example of an analysis meth od for use in solder alloys in general.