The high-temperature operation life test (HTOL) was conducted in this paper to study electromigration phenomena of solder interconnects in a flip-chip package assembly. We examined the fatigue reliability and morphological patterns of three solder compositions: Sn-4Ag-0.5Cu, Sn-3.5Ag-1Cu, and Sn-3Ag-1.5Cu, subjected to two test conditions consisting of different average current densities and ambient temperatures (5kA∕cm2 at 150°C and 20kA∕cm2 at 30°C). It is interesting to realize that as the Cu weight content of the solder composition increases, the fatigue life increases under 5kA∕cm2 at 150°C but decreases under 20kA∕cm2 at 30°C. Observed electromigration morphologies along with computed current density and temperature distributions on solder interconnects from the electrothermal coupling analysis were examined, correlated, and discussed.

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The electromigration reliability of solder interconnects is dominated by the current density and the temperature inside the interconnects. For flip-chip packages, current densities around the regions where traces connect a solder bump increase by a significant amount owing to the differences in feature sizes and electric resistivities between the solder bump and its adjacent traces. This current crowding effect along with induced Joule heating accelerates electromigration failures. In this paper, effects of current crowding and Joule heating in a flip-chip package are examined and quantified through a three-dimensional electrothermal coupling analysis. We apply a volumetric averaging technique to cope with the current crowding singularity. The volumetrically averaged current density and the maximum temperature in a solder bump are integrated in the Black's equation to calibrate experimental electromigration fatigue lives.