The existence of an incubation stage before edge drift occurred was found by examining the electromigration characteristics of eutectic SnPb solder in an edge drift structure using in situ scanning electron microscopy and the interruptive test method. During this incubation stage, the depletion of Pb was observed at the cathode end. From the change in resistance, the activation energies for the incubation and edge movement stages were calculated to be 0.88 and 1.02eV, respectively. Based upon a comparison of the activation energies for each stage with the previously reported values, it was believed that, during the incubation stage, Pb migrated before Sn and that the edge movement resulted from the migration of Sn. These results suggested that Pb depletion was a prerequisite for electromigration-induced void nucleation in eutectic SnPb solder.

Relationship between Edge Drift and Atomic Migration during Electromigration of Eutectic SnPb Lines. M.S.Yoon, S.B.Lee, O.H.Kim, Y.B.Park, Y.C.Joo: Journal of Applied Physics, 2006, 100[3], 033715 (6pp)