Temperature Effect on Intermetallic Compound Growth Kinetics of Cu Pillar/Sn Bumps

The in situ intermetallic compound (IMC) growth in Cu pillar/Sn bumps was investigated by isothermal annealing at 120A degrees C, 150A degrees C, and 180A degrees C using an in situ scanning electron microscope. Only the Cu6Sn5 phase formed at the interface between the Cu pillar and Sn during the reflow process. The Cu3Sn phase formed and grew at the interfaces between the Cu pillar and Cu6Sn5 with increased annealing time. Total (Cu6Sn5 + Cu3Sn) IMC thickness increased linearly with the square root of annealing time. The growth slopes of total IMC decreased after 240 h at 150A degrees C and 60 h at 180A degrees C, due to the fact that the Cu6Sn5 phase transforms to the Cu3Sn phase when all of the remaining Sn phase in the Cu pillar bump is completely exhausted. The complete consumption time of the Sn phase at 180A degrees C was shorter than that at 150A degrees C. The apparent activation energy for total IMC growth was determined to be 0.57 eV.