Junichi Machida, Hisao Esaka, Manabu Tamura and Kei Shinozuka
Department of Materials Science and Engineering, National Defense Academy, Yokosuka 239-8686
The Sn-Cu binary eutectic alloy is one of candidate alloys for lead-free solder. In order to investigate the evolution of solidified structure of Sn-Cu binary eutectic alloy, the unidirectional solidification technique has been applied using a Bridgman type furnace.
Primary β-Sn exhibits dendrite morphology, on the other hand, a primary Cu6Sn5 indicates a faceted crystal, the cross section of which is typically H-shaped and eutectic structure is rod-like. Coupled growth zone of this alloy system is found to be extended to Cu-rich side and to be rather symmetric. This may be due to the difference in undercooling for growth of Cu6Sn5, β-Sn and eutectic phases. Jackson parameter of Cu6Sn5 is deduced to be high comparing with β-Sn.
coupled-zone, lead-free solder, undercooling, unidirectional solidification, eutectic growth
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