Interface reaction between copper and molten tin-lead solders

The formation and growth of Cu-Sn intermetallic film at the interface betwe en molten Sn-Pb solders and Cu were studied at different temperature and ex posure times. The eta -phase (CU6Sn5) was observed to form at all condition s except at the lowest Sn level of 27 wt% and at the two highest temperatur es of 290 and 310 degreesC. The epsilon -phase (Cu3Sn) was then obtained. A t high Sn contents and short times, a cellular film with a rugged interface was obtained which evolved into a compact film with a scalloped interface as the Sn content decreased and exposure time increased. The epsilon -phase film always formed with a relatively planar interface. The intermetallic g rains showed preferred crystallographic orientations. Thickness measurement s showed that the net growth rate depends not only on diffusion through the film but also on the film dissolution. Precipitation of the eta -phase whi skers was detected during cooling, particularly when the temperature was si gnificantly high. (C) 2001 Acta Materialia Inc. Published by Elsevier Scien ce Ltd. All rights reserved.