Real time synchrotron X-ray imaging for nucleation and growth of Cu_6Sn_5 in Sn-7Cu-0.05Ni high temperature lead-free solder alloys

摘要

This paper demonstrates how recent progress for real-time solidification observation at SPring-8 synchrotron has contributed to the development of Sn-7wt%Cu-0.05wt%Ni high temperature lead-free solder alloys. Lead-free solder alloys in the composition range Sn-0.7 to 7.6wt%Cu that consist of primary Cu_6Sn_5 in a eutectic Sn-Cu_6Sn_5 matrix have been proposed as solders for application at temperatures up to 400°C for the assembly high current semiconductors. It is shown that trace levels of Al have a marked effect on the solder microstructure and refine the size of the primary Cu_6Sn_5. The solidification pathway that leads to the refinement was observed in real-time using X-ray synchrotron observations.