A study of electromigration in 3D flip chip solder joint using numerical simulation of heat flux and current density

This paper applies an analogy between heat flow and current flow to examine the current density distribution in a solder interconnect, which has a direct relationship with the atomic flux movement. From a 3D heat conduction analysis, we discover that the heat flux distribution in the solder bump is a strong function of the direction of heat flow. If the heat flow turns 90 degrees when it leaves the solder bump, the high heat flux region will also turn 90 degrees. From a cross-sectional view of the mean heat flux, the high heat flux (or current flux) region in the solder moves from the top of the UBM region to the lower right corner, and the right side of the solder has the highest flux density. This result correlates well with the experimental data where the measured atomic flux in the left side of the solder is less than in the right side. Two other cases with 0 and 180-degree heat flows also illustrate the difference in heat flux distribution. This suggests that the current density distribution in the solder changes as the direction of the current flow changes.