We report an unusual circuit failure mode induced by short-lived extrusions observed during DC and AC electromigration (EM) tests of quarter-micron damascene copper interconnects. This novel “soft” failure mode consists of extrusions forming, then self-dissolving before the traditional permanent void or extrusion failure. These failures shorten the lifetime significantly and bring new challenges to reliability tests. Two self-dissolution mechanisms under DC test conditions are discussed and extrusion shape evolution is modeled assuming both capillary and electron wind forces are present. Our model confirms that the electrical stress will accelerate the shape evolution process.