In-Situ Observation of Electromigration in Eutectic SnPb Solder Lines: Atomic Migration and Hillock Formation
The real-time microstructural evolution during electromigration of eutectic SnPb solder lines with an edge drift structure was examined using an in-situ scanning electron microscope (SEM) technique. The test temperature and the current density were either 100°C or 50°C and 6 × 104 A/cm2 or 8 × 104 A/cm2, respectively. In-situ microstructural observation of the depleted phases and quantitative analysis of the number of hillock phases made it clear that the dominant migrating element and dominant hillock phase were Sn and Pb at room temperature, respectively, while both dominant migrating element and dominant hillock phase were Pb at 100°C. Such temperature dependence of the dominant hillock phase in the eutectic SnPb solder can be understood by considering the atomic size factors of the metallic solid solutions. We suggest that at high temperature, it is easier for Pb atoms to be injected into the Pb phase (Pb-phase hillocks); while at low temperature, Pb-phase hillocks were squeezed by Sn, which penetrated the Pb phase.
KeywordsElectromigration eutectic SnPb hillocks in-situ observation
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This work was supported by the Center for Electronic Packaging Materials, Korea Science and Engineering Foundation, and by the Ministry of Education and Human Resources Development (MOE), the Ministry of Commerce, Industry and Energy (MOCIE), and the Ministry of Labor (MOLAB) through the fostering project of the Lab of Excellency. Y.-C. Joo acknowledges a 2005 LG Yonam Foundation Fellowship for the partial support of his stay at Stanford University.