Characterization of small-sized eutectic Sn-Bi solder bumps fabricated using electroplating |
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Authors: | Hoe-Rok Jung Hyuk-Hwan Kim Won-Jong Lee |
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Affiliation: | (1) Department of Materials Science and Engineering, Korea Advanced Institute of Science and Technology, 305-701 Daejeon, Korea |
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Abstract: | We studied the effects of the cooling rate during the reflow process on the microstructure of eutectic Sn-Bi solder bumps
of various sizes fabricated by electroplating. To fabricate eutectic Sn-Bi solder bumps of less than 50 μm in diameter, Sn-Bi
alloys were electroplated on Cu pads and reflowed at various cooling rates using the rapid thermal annealing system. The interior
microstructure of electroplated bumps showed a fine mixture of Sn-rich phases and Bi-rich phases regardless of the cooling
rate. Such an interior microstructure of electroplated bumps was quite different from the reported microstructure of vacuum-evaporated
bumps. Ball shear tests were performed to study the effects of the cooling rate on the shear strength of the solder bumps
and showed that the shear strength of the bumps increased with increasing cooling rate probably due to the reduced grain size.
Soft fractures inside the solder bump were observed during the ball shear test regardless of the cooling rate. |
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Keywords: | Sn-Bi solder bump electroplating reflow bump size shear strength |
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