An Investigation of Microstructure and Microhardness
of Sn-Cu and Sn-Ag Solders as Functions of Alloy Composition and Cooling Rate |
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Authors: | Sun-Kyoung Seo Sung K Kang Da-Yuan Shih Hyuck Mo Lee |
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Affiliation: | (1) Department of Materials Science and Engineering, KAIST, 335 Gwahangno, Yuseong-gu, Daejeon, 305-701, Republic of Korea;(2) IBM T.J. Watson Research Center, Yorktown Heights, NY 10598, USA |
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Abstract: | The microstructure and microhardness of Sn-xAg and Sn-xCu solders were investigated as functions of alloy composition and cooling rate. The Ag compositions examined varied from
0.5 wt.% to 3.5 wt.%, while Cu varied from 0.5 wt.% to 2.0 wt.%. Three cooling rates were employed during solidification:
0.02°C/s (furnace cooling), about 10°C/s (air cooling), and 100°C/s or higher (rapid solidification). Sn grain size and orientation
were observed by cross-polarization light microscopy and electron-backscattering diffraction (EBSD) techniques. The microhardness
was measured to correlate the mechanical properties with alloy compositions and cooling rates. From this study, it was found
that both alloy composition and cooling rate can significantly affect the Sn grain size and hardness in Sn-rich solders. The
critical factors that affect the microstructure–property relationships of Sn-rich solders are discussed, including grain size,
crystal orientation, dendrite cells, twin boundaries, and intermetallic compounds (IMC). |
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Keywords: | Sn-Ag Sn-Cu microstructure Sn grain microhardness cooling rate |
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