Yoshiko Takamatsu, Hisao Esaka and Kei Shinozuka
Department of Materials Science and Engineering, National Defense Academy of Japan, Yokosuka 239-8686
As a result of extensive studies, binary-eutectic Sn-Ag or Sn-Cu alloys have been identified as the leading candidates for lead-free solder. In these alloys the large β-Sn dendrites, such as pseudo-primary dendrite, are often observed. This study has been performed to estimate the volume fraction of β-Sn in hyper-eutectic and eutectic alloys under the presence of intermetallic compound as a primary phase.
In this study, Sn-X, where X=Cu, Ag and Ni, binary alloys were used. To reveal the volume fraction of β-Sn more clearly, various compositions were used, and these alloys were solidified at two cooling rates (0.05°C/s and 0.70°C/s).
The volume fraction of β-Sn increased with increaing of the undercooling for β-Sn formation. The estimation model for volume fraction of β-Sn was developed. It was found that the estimated value agreed with the measured value even though the alloy system was different.
lead-free solder, tin-silver alloy, tin-copper alloy, tin-nickel alloy, β-tin phase, undercooling, volume fraction, nucleation, intermetallic compound
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