Reliability testing of Cu-Sn intermetallic micro-bump interconnections for 3D-device stacking

In this work, two different reliability experiments, thermal cycling and electromigration, are performed on fully packaged Si-to-Si stacks bonded with Cu-Sn intermetallic (IMC) micro-bumps. These experiments investigate both the more critical thermo-mechanical behavior as well as the expected positive thermal-electrical behavior. The Cu-Sn IMC bumps survive thermal cycling for more than 3900 cycles between −40 and 125°C with 1 hour per cycle. The resistance to electromigration is strongly dependant on the used Sn thickness and shows an improved performance for thinner Sn samples (3.5µm) compared to thicker Sn (8µm). In either case, IMC bumps outperform standard solder flip chip bumps.