Kinetics of the η–η′ transformation in Cu6Sn5

Cu6Sn5 is an important intermetallic compound used in lead-free soldering and anode materials for Li-ion batteries. Cu6Sn5 exists in at least two crystal structures, with a transformation from hexagonal η-Cu6Sn5 at temperatures higher than ∼186 °C to monoclinic η′-Cu6Sn5 at lower temperatures. Using variable temperature synchrotron X-ray diffraction analysis, the kinetics of the η–η′ transformation are investigated and a time–temperature transformation diagram is partially developed. The significance of the results in terms of phase and dimensional stability in solder joints are discussed.