A Comparison of Flip Chip Bump Electromigration Reliability for Cu Pillar, High Pb, SnAg, and SnPb Bump Structures

Electromigration failure in flip-chip bumps has emerged as a major reliability concern due to potential elimination of Pb from flip-chip bumps and a continuous drive to increased IO density resulting in a reduction of bump size and pitch. Traditionally, flip-chip interconnects incorporate a high Pb bump soldered with a SnPb eutectic paste to the substrate or another die. However, because of RoHS directives, the industry is responding with Pb free bump development, such as SnAg bump with SAC solder or Cu Pillar with SAC/SnAg solder. Although a number of recent publications deal with electromigration reliability of Pb free and Cu Pillar bumps, a gap exists in terms of their performance comparison with high Pb and SnPb solder on the same bump geometry. The available test data is based on different test vehicles and it becomes difficult to determine the relative performance of these different metallurgies under accelerated test conditions. In addition, not all published data provides the essential parameters ...