In situ study on growth behavior of Cu_6Sn_5 during solidification with an applied DC in RE-doped Sn-Cu solder alloys

摘要

The growth behavior of Cu_6Sn_5 intermetallic compounds in rare earth (RE)-doped Sn-Cu solder alloys with an applied direct current (DC) has been in situ investigated using synchrotron radiation imaging technology. The morphological evolutions of Cu_6Sn_5 with various shapes of I-like, Y-like and bird-like are directly observed. After doping RE, the number of I-like and bird-like Cu_6Sn_5 is decreased, but the number of Y-like Cu_6Sn_5 is increased. The morphologies of Cu_6Sn_5 are more uniform and the mean lengths of Cu_6Sn_5 of different shapes are reduced in RE-doped alloys compared with that in RE-free alloys, which is attributed to the adsorption effect of RE. The growth orientation of Y-like Cu_6Sn_5 is changed after La is doped. Additionally, with an applied DC, the nucleation rate of Cu_6Sn_5 is increased and the growth rate is markedly enhanced resulting in the refinement of Cu_6Sn_5. Furthermore, the mechanisms of refinement caused by RE and DC are specifically discussed.