The preferential growth of η-Cu6Sn5 on (111) uni-directional Cu pads

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 ?-Cu
6
Sn
5
s have shown a preferential growth relationship on the uni-directional Cu. At the early stage of reflowing, the orientations of Cu
6
Sn
5
were preferred at (0001). As the time of reflow extended, the orientations of Cu
6
Sn
5
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 Cu
6
Sn
5
. With the technique of electroplating (111) uni-directional Cu, it is possible to control the orientations of intermetallics in the solder joints.