Thermomigration in eutectic tin-lead flip chip solder joints

Abstract

The thermomigration of eutectic tin-lead flip chip solder joints under ambient temperatures of 20 degC, 100degC and 150degC was investigated in terms of microstructural evolution. No significant thermomigration occurred after 100 h at 20degC and at 100degC. Only microstructural coarsening was observed in solder joints for these cases. However, Pb thermomigration and phase segregation were observed in solder joints after only 50 h at 150degC. Measurements showed that the temperature difference between the chip side and the substrate side reached 8.1degC (a temperature gradient of about 2700degC/cm across the solder joints) at an ambient temperature of 150degC. It is believed that Pb atoms migrated from the chip side (the hot side) to the substrate side (the cold side) under a temperature gradient of 2700 degC/cm