Abstract
Under the rapid development of consumer electronics products, the packaging technique had also improved in order to meet the demand for high performance, small size and multi-function. In the flip chip packaging technology, it provides more I/O counts with same area, while reducing the size. However, with smaller solder bump, an increase in current density is enough to cause the electromigration in flip chip solder joint. Thus, electromigration has become a serious reliability problem in recent years. In addition, the three-dimensional integrated circuit (3D IC) packaging technology has been developed for the further demands on higher performance and miniaturization of electronics products, which using the microbumps and through silicon vias (TSV) to stack and connect with different silicon chip. With much smaller solder bump and greater increased current density, more severe reliability issue is expected to be the key to this new developing technology. In this thesis, the effect of solder length on void formation and IMCs dissolution under current stressing was discussed, especially when 3D IC technology used smaller solder bumps decreased and thicker Cu metallization. The electromigration tests were performed on the line-type Cu/Sn/Cu solder strips in order to direct investigation of electromigration effect, which excluding others complicated factors, i.e. current crowding effect and temperature gradient. By using photolithography and sputtering, the solder strips of various lengths, including 300, 150, 100, 75, 50 and 25 μm, can be fabricated. Two main failure behaviors were found to be affected by solder length under current stressing, including the void formation induced by the diffusion of Sn and the IMCs dissolution induced by the diffusion of Cu under current stressing by 3×103 and 8×103A/cm2 at 75°C. Both failure behaviors become more serious when the solder length increases. The corresponding mechanism and kinetic analysis for both length-dependent void formation and dissolution of IMCs was discussed. Moreover, no electromigration induced void formation and dissolution of IMCs was observed at certain solder length. The critical length to trigger dissolution of IMCs under current stressing was also obtained. Through the results in this thesis, the effect of solder length on electromigration behavior under current stressing was further clarified.