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Thermal-Electric-Mechanical coupling simulation of Cu Pillar Bumps under AC current

With the development of 3D IC, the electromigration of Cu pillar bumps under AC conditions is currently given wide attention. The thermal-electric-mechanical coupling simulation was realized by using the direct coupling element of ANSYS software. We find out that the maximum thermal gradient (TG) is located at IMC layer in the Cu pillar bumps. Due to the large CTE mismatch between the Cu trace and the Si chip, the maximum stress is occurred within the Cu trace. The maximum current density (JS) is located in the middle of the Cu trace and at the corner of the Cu pillar. In addition, during the loading of AC current, with the increase of loading time, the stress and temperature will both increase in the early stage of loading. However, with the current loading continues (t ⩾ 0.625s), the temperature and stress gradually maintain at a stabilized level, but show significant fluctuation. With the increase of current frequency, the curves of fluctuation stage will be more and more smooth, and gradually fit to the curve of DC. It is also found that there is a lag between temperature/stress and AC current in the fluctuation stage.