Microstructure Control of Uni-directional Growth of Η-cu6sn5 in Microbumps on (111) Oriented and Nanotwinned Cu

The growth of η and η’-Cu6Sn5 has been proven as a preferential growth behavior on single crystal copper. However, a layer of single crystal copper is not possible to be electroplated. It can not be utilized in the electronic industry. In this paper, we electroplated an array of (111) uni-directional Cu pad followed by electroplating SnAg2.3. After being reflowed at 260C for 1 minute, the η-Cu6Sn5 showed a preferential growth to (0001) plane. As reflow time extended, the preferential growth behavior would change. The intensity of (0001) decreased while that of (2 3) increased. It means the preferential growth of η-Cu6Sn5 would change during reflow. Eventually, the preferred orientation of η-Cu6Sn5 changed to (2 3) after 5 minutes of reflowing. It is also found that this preferential growth behavior of Cu6Sn5 would be affected by the quality of (111) uni-directional Cu.