Development of Multi-Die Stacking with Cu-Cu interconnects using Gang Bonding Approach

Cu is prefer interconnects as compared to solder interconnects as it offered no risk of solder merging, finer pitch, no intermetallic compound formation and better electrical characteristic. However, the implementation of CuCu interconnects is not a trivial matter. It needs to overcome many challenges such as copper oxide formation, long bonding duration and stringent requirement on co-planity of Cu bump height. In this paper, we used Gang Bonding as the bonding approach to form Cu-Cu interconnects. The multi-dies were stacked on top of each other across the whole wafer without forming any interconnect. Cu-Cu interconnects were only formed between the die stacking through the application of pressure, temperature and time in the gang bonding process. Good Cu-Cu interconnects through the gang bonding approach was demonstrated successfully.