This paper reports a peculiar growth and segregation behavior of IMC in a flip chip joint with Sn2.4Ag solder bump under electrical current stressing. A set of two neighboring solder joints were adopted for investigation at 1.5∼3.0×104 A/cm2 of current stressing at various temperatures up to 180°C. One of the joint experiences current flow from substrate to the Si chip while opposite for the other joint. The size analysis with SEM imaging shows that the Ag3Sn IMCs formed in the bulk during current stressing grows following the empirical equation Δr (radius change) = ktn with n =1.1, indicating a reaction controlled kinetics. The activation energy of the Ag3Sn IMC growth was estimated to be 11.5 (at 3.0 × 104 A/cm2) ∼14.0 (at 1.0×104 A/cm2) kJ/mole. Both Cu6Sn 5 and Cu3Sn were formed at the joint/metallization interface, while only Cu6Sn5 were found in the bulk. The SEM investigation at various cross sections from center to one end of the hemisphere for a joint, current stressed with 1.5×104A/cm 2 at 180°C for 330 hours, shows a serious segregation of the Cu6Sn5 IMC closing to the end portion of the bump. A mechanism incorporating IMC dissolution, electromigration, and thermomigration was proposed to explain the segregation behavior.