Geometric size effects on the elements consuming at the solder pad under current stressing

Abstract

This paper investigated the geometric size effects on elements consuming at the solder pad under current stressing. The micro solder joints Cu/Sn-3.0Ag-0.5Cu(SAC305)/Cu with same volume and different heights (H1=300μm, H2=420μm and H3=520μm) were made for the electromigration test. The results indicated that the consumption of copper element at the solder pad increased with the increase of the height of the solder joints after reflow. In the electro-thermal aging test, the consumption of copper element at the cathode solder pad increased linearly with the increase of stressing time, and the average consumption rate increased with the increase of the height of the solder joints. It is suggested that the solder joints with a higher bump height had a lower dispersion of current density, which resulted in a higher current density in the migration routine of the metal atoms. Current density is the dominant driving force in the process of the electromigration. However, the consumption of copper element at the anode solder pad increased linearly with the increase of the square root of stressing time, and the average consumption rate has the same law with that at the cathode. The numerical simulation was also conducted under the same stressing conditions as the experimental tests. The results revealed that the solder joint with a higher bump height had a lager internal current density, which is consistent with the experimental results.