Orientation transformation of Pb grains in 5Sn-95Pb/63Sn-37Pb composite flip-chip solder joints during electromigration test

Microstructural evolution occurred in 5Sn-95Pb/63Sn-37Pb composite flip-chip solder bump during electromigration. Scanning electron microscopy (SEM) and electron backscatter diffraction (EBSD) observations for 5Sn-95Pb/63Sn-37Pb composite flip-chip solder joints subjected to 5 kA/cm² current stressing at 150 °C revealed a gradual orientation transformation of Ph grains from random textures toward (101) grains. We proposed that the combination of reducing the surface energy of Pb grain boundaries and resistance of the entire polycrystalline system are the driving force for the orientation transformation of Ph grains during an electromigration test.