The preferential growth of #x03B7;-Cu6Sn5 on (111) uni-directional Cu pads

摘要

The uni-directional Cu with surface covered by (111) plane can be made by electroplating. The shape of Cu grain was columnar. The diameters of these columnar grains were 2 – 5 µm. After electroplating SnAg2.3 on the Cu pad and then reflowed at 260 oC, the ?-Cu6Sn5s have shown a preferential growth relationship on the uni-directional Cu. At the early stage of reflowing, the orientations of Cu6Sn5 were preferred at (0001). As the time of reflow extended, the orientations of Cu6Sn5 would change to be preferred at (2113). Since the uni-directional Cu was still poly-crystal metal, the coherence must be achieved by Cu-Sn bonding at the interface between Cu pads and the intermetallics. Electroplating parameters would affect the quality of uni-directional Cu and therefore affecting the preferential behavior of Cu6Sn5. With the technique of electroplating (111) uni-directional Cu, it is possible to control the orientations of intermetallics in the solder joints.