Electromigration reliability of cylindrical Cu pillar SnAg3.0Cu0.5 bumps

The main trends in consumer electronics are increasing performances of their products and a reduction of the costs. These trends lead to an ongoing integration on package level which leads to a decreasing size of the solder contacts. This goes along with a higher sensibility to thermal-mechanical stress and void formation due to electromigration (EM). Against this background copper pillar bumps were introduced, because they combine the robustness of metal wire bonds with the low bonding pressure of reflow soldering. Experimental results have shown a longer lifetime of Cu pillar bumps during EM tests, but a continuative analysis is still needed for design optimization. Against this background a finite element analysis (FEA) was performed to compare the EM induced mass flux in conventional solder bumps and in two different designs for Cu pillar bumps. The thermal electrical simulations were performed with ANSYS^®. Afterwards a user routine was used to calculate the EM induced mass fluxes and mass flux divergences. The simulation results are used to identify possible reasons for the increased EM performance of Cu pillar bumps and they enable the identification of preferable designs.