Lawrence Berkeley National Laboratory

Wetting reaction between molten Sn-based solders and Cu produces scallop-type Cu6Sn5. In the present wetting study, a (001) single crystal Cu is used as substrate and a dramatic change in the morphology of Cu6Sn5 is observed: instead of scallop type, the authors observed a rooftop-type Cu6Sn5 grains, elongated along two preferred orientation directions. This was confirmed by electron beam backscattered diffraction and white beam synchrotron x-ray microdiffraction. The results indicate that the nucleation, growth, and ripening behavior of Cu6Sn5 on single crystal substrate can be quite different from the conventional case of wetting on randomly oriented polycrystalline Cu substrates. (14 References).