ABSTRACT
Electromigration (EM) and Thermomigration (TM) or Soret Effect are classes of mass transport resulting from the momentum transfer between conducting electrons and diffusing metal atoms. They occur in any material carrying electrical current (EM) or sustaining a temperature gradient (TM), but inmost applications, it is negligible and can be ignored. Occurring when diffusion rates are relatively rapid and in the presence of high direct current densities, electromigration has been identified as a major potential failure mechanism in semiconductor devices. Millions, perhaps billions, of dollars have been expended over the past few decades understanding and controlling this phenomenon. Remarkable progress has been made in the past decade in understanding the physics and materials science of electromigration, and this knowledge has enabled reasonably accurate reliability predictions and significant reliability enhancements through effective design rules governing on-chip metallization. Although there is very little published data concerning solder materials and electromigration, there is every reason to believe that what has been learned with other metal systems can be applied to solder materials as well.
