Thermomigration in Pb-free SnAg solder joint under alternating current stressing

Abstract

Lead-free solders have been adopted by the microelectronics industry. However, their thermomigration behaviors are unclear. Thermomigration in eutectic SnAg3.5 solder joints was investigated using an alternating current (ac) of 0.57 A at 100 degrees C. The ac eliminates the electromigration effect and creates a thermal gradient of 2829 degrees C/cm, facilitating the study of thermomigration. Arrays of tiny markers fabricated by a focused ion beam are employed to measure the thermomigration rate. It is found that Sn atoms migrated toward the hot end. The thermomigration flux and molar heat of transport are measured to be 5.0x10(12) atoms/cm(2) and 1.36 kJ/mole, respectively.