Kinetics of the polymorphic phase transformation of Cu6Sn5

Cu6Sn5 is a critical intermetallic compound in soldering and three-dimensional integrated circuit packaging technology and exists in at least five different crystal structures in the solid state, with a polymorphic phase transformation from hexagonal to monoclinic structures occurring on cooling. The kinetics of polymorphic transformations in Sn-rich Cu6Sn5 and Cu-rich Cu6Sn5 is systematically investigated in this study. This includes the generation of continuous cooling transformation diagrams as well as time-temperature transformation diagrams. Techniques used include variable temperature synchrotron powder X-ray diffraction and differential scanning calorimetry. The findings have important implications for the manufacture of solder joints and their in-service performance.