Electromigration in eutectic SnPb solder lines

We have prepared eutectic SnPb solder lines for electromigration study by a process of solder reflow into V-grooves etched on (001) Si wafer surfaces. They are thick lines and are highly reproducible. We report here results of lines of 100 μm in width and 150 to 800 μm in length, stressed by a current density of 2.8×104 A/cm2 at 150 °C in ambient. The accumulation of a large lump of solder, rather than hillocks of Sn and Pb, was observed at the anode, and depletions and voids were observed at the cathode. By measuring the volume of the lump, we have calculated the average effective charge number of electromigration in the eutectic solder to be 33, which is close to the reported value of 47 for self-electromigration in bulk Pb. Using x-ray dispersive analysis, we found that Pb is the dominant diffusing species.