Thermomigration in Pb–Sn solder joints under joule heating during electric current stressing

Abstract

Electromigration of solder joint under high dc current density is known as a reliability concern for the future high-density flip chip packaging and power packaging. Biased mass diffusion within solder joint from cathode to anode under high dc current density is observed in these experiments. In this letter, the experiments on flip chip solder joints under dc current stressing are conducted and thermomigration due to the thermal gradient in the solder joint caused by joule heating is reported. A three-dimensional coupled electric thermal finite-element (FE) simulation of a realistic flip chip module shows the existence of thermal gradient in the solder joint which is high enough to trigger thermomigration.

Current-Induced Phase Partitioning in Eutectic Indium-Tin Pb-Free Solder Interconnect

“…The entire sample fixture was immersed in a heat-conductive oil bath to minimize temperature gradient and temperature rise, as both are known to induce thermomigration in solder joints. 10 The current density at which the solder joint becomes liquid is taken as the critical current density. Using a high magnification microscope, we tested multiple samples, and the average critical current density was determined to be 2.8 · 10 4 A/cm 2 .…”

Thermomigration in lead-free solder joints

“…He concluded that a flux of salt was generated by a temperature gradient, which results in a concentration gradient in steady state conditions (Platten, 2006). Ye et al (2003e) showed that the same process also takes place in solder alloys. Experimental studies suggest that the effect of thermomigration on solder joint reliability is as serious as that of electromigration (Ye et al, 2003b;2003c;2003e;Huang et al, 2006;Roush and Jaspal, 1982).…”

“…They found that Sn moved to the hot end while Pb moved to cold end. Ye et al (2003e) reported thermomigration may assist electromigration if the higher temperature side coincides with the cathode side, and counter electromigration if the hot side is the anode side.…”

“…Electromigration causes mass accumulation and hillocks formation in the anode side, and vacancy condensation and void formation in the cathode side (Ye et al, 2003a;2003e). Both hillocks and voids will cause the degradation of the solder joint and eventual failure.…”

“…It is well known that the high current density and high temperature gradient induce mass migration that degrades the solder joints (Ye, 2004;Ye et al, 2003a;2003e). The two primary mass migration processes that manifest in solder joints subjected to high current density are electromigration and thermomigration (Ye, 2004;Ye et al, 2003a;2003b;2003c;2003e;Basaran et al, 2003;Huang et al, 2006;).…”