In flip chip technology, electromigration affects the reliability of the solder interconnections. When investigating electromigration in the solder joint, it is essential to examine the effective charge number (Z*) of the atoms involved in the electromigration. In this study, first, a solder joint with almost equivalent current crowding on electromigration was produced by using 1mm thick Cu plates. After that, nine markers were formed on the cross-sectioned solder joint. Then, the migration length of each marker was systematically measured under two conditions. The Z* of each marker was examined by the marker's migration length.