Melting of eutectic SnPb flip chip solder joints has been observed to occur frequently in dc electromigration tested with current density above 1.5× 104 A cm2 at an ambient temperature of 100 °C. It has been found that it is not due to the Joule heating of the solder bump itself, but rather due to the Joule heating of the on-chip Al interconnects. The current density in the Al approaches 2× 106 A cm2 and electromigration has especially generated voids at the anode of the Al. The damage has greatly increased the resistance of the Al, which produces the heat needed to melt the solder joint. The results of electrothermal coupling analysis show that when the resistance of the Al line changed threefold, the solder bump melted.