Abstract
Thermomigration often occur accompanying with electromigration in solder joint, due to joule heating and current crowding induced temperature gradient. Previous studies have suggested that when the temperature gradient is larger than 1000˚C/cm, thermomigration may occur. However, the influence of ambient temperature on thermomigration of solder joints has not been reported yet. To understand how ambient temperature affects the thermomigration of solders, a constant current was applied on flip chip solder to establish a temperature gradient under five ambient temperatures. The results suggest that a critical temperature is required to trigger thermomigration when the temperature gradient is given. No thermomigration induced damage was found in unpowered solders for samples tested below 125℃; whereas thermomigration induced phase redistribution was observed for samples tested above 150℃. The corresponding mechanism will be proposed and the theoretical critical temperature to trigger thermomigration in term of different temperature gradient will also be discussed.