A Brief Review on Electromigration Behaviours of Solder Joints Under Electrothermal Load

Solder joints in electric devices have been reducing in size for decades. The drive to fit more functions into a single device or package continues to drive innovation in the field. Surface mounted chip-sized components like resistors are now widespread in sizes of 0402 and $0201(1 \times 0,5 \mathrm{~mm}$ and $\mathbf{0, 6 x 0, 3 ~ m m}$) and less, while BGA solder joints are even smaller, with chiplet technology driving inter-chip solder bumps into $\leq 100 \mu \mathrm{~m}$ range. The reduction in solder joints size means that the current density in the solder joint and the thermal load on the joint could be significantly higher than in the case of larger components. The increased electrothermal load may increase the components’ tendency to show electromigration or thermomigration phenomena. These can lead to Cu pad dissolution, recrystallization and intermetallic compound (IMC) thickening, all of which could influence the mechanical properties of the solder joints. Literature have shown that electromigration can reduce the reliability of the solder joints, however, there is an increasing need to validate electromigration or thermomigration in a robust manner. This paper is a review of current literature on electromigration behaviours in small scale solder joints, dealing with topics such as the effect of using different solder materials.