Abstract
Packaging technology is currently transitioning from flip chip technology to three dimensional integrated circuits (3D IC) package. In the flip chip technology, a temperature difference of 10 ºC across a 100-um-diameter solder joints is sufficient to induced thermomigration. In 3D IC, the diameter of solder ball is reduced by a factor of 10, suggesting that a temperature difference of 1 ºC across a 10-um-diameter solder joints will cause thermomigration failure. In this talk, the temperature gradient-induced voids formation on the Pb-free solder regarding different bump heights is reported. When the bump height is 90 um in the flip chip sample, the voids were nucleated at the cold side; however, when the bump height is shrunk to 6um in the 3D IC sample, the voids were found to form at the hot end. The mechanism of Kirkendall void formation on both samples is proposed and compared.