Nucleation of tin on the Cu6Sn5 layer in electronic interconnections.

A Cu 6 Sn 5 layer is an integral part of many electronic interconnections. Here we show that, although primary Cu 6 Sn 5 is not a potent nucleant for Sn, the Cu 6 Sn 5 layer plays a key role in Sn nucleation and microstructure formation in solder joints. Combining thermal analysis, FIB-tomography and EBSD, we show that conical cavities are present between the scallops of the Cu 6 Sn 5 layer that act as geometric nucleation sites for Sn, that Sn grows from the Cu 6 Sn 5 layer, and that reproducible nucleation orientation relationships (ORs) exist between Cu 6 Sn 5 and Sn. With these ORs, a near-random distribution of Sn orientations is predicted from joint to joint even for Cu 6 Sn 5 layers with a strong [0001] fibre texture. It is shown that the nucleation undercooling is strongly affected by manipulation of the Cu 6 Sn 5 layer shape, and that it is possible to prevent nucleation on the Cu 6 Sn 5 layer by adding more potent nucleants. [ABSTRACT FROM AUTHOR]