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The electromigration failure mechanism in flip-chip solder joints through the rapid dissolution of the Cu metallization was studied in detail. The ambient temperature was found to be a very important factor in this failure mechanism. When the ambient temperature was changed from 100°C to 70°C, the time to failure changed from 95 min to 31 days. The results of this study indicate that temperature, as an experimental variable, is not less important than the current density in electromigration study. The surface temperatures of the chip and substrate during electromigration were also measured. The temperature of the Si chip was reasonably homogeneous because of the fact that Si is a very good thermal conductor. It was also reasoned that the high thermal conductivity of the PbSn solder could not support a temperature gradient large enough to induce thermomigration across the solder joint in the present study. Experimentally, no evidence of mass transport caused by thermomigration was observed. [ABSTRACT FROM AUTHOR]