Temperature Dependence of Dominant Hillock Phases during Electromigration of Eutectic SnPb Solder Lines

In-situ observation by scanning electron microscope of the microstructure evolution near the cathode depletion region and the quantitative analysis on the number of hillock phases in the eutectic SnPb edge drift structure made it clear that the dominant migrating element and dominant hillock phase were Sn and Pb, respectively, under 50 oC while both dominant migrating element and dominant hillock phase were Pb above 100 oC. Such temperature-dependence of the dominant hillock phases in the eutectic SnPb solder can be understood by considering the atomic size factors of the metallic solid solutions.