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| Content Provider | IEEE Xplore Digital Library |
|---|---|
| Author | Xian, J.W. Belyakov, S.A. Britton, T.B. Gourlay, C.M. |
| Copyright Year | 2015 |
| Description | Author affiliation: Imperial Coll. London, London, UK (Xian, J.W.; Belyakov, S.A.; Britton, T.B.; Gourlay, C.M.) |
| Abstract | $Cu_{6}Sn_{5}$ is a common intermetallic in Pb-free soldering, and the volume fraction, size and shape of $Cu_{6}Sn_{5}$ particles in the bulk solder plays an important role in the reliability of solder joints. We have previously shown that Al additions can significantly reduce the size of primary $Cu_{6}Sn_{5}$ crystals in Sn-Cu-Al alloys, due to epitaxial nucleation of $Cu_{6}Sn_{5}$ on either $Cu_{33}Al_{17}$ or $Cu_{9}Al_{4}$ particles [1]. In this paper, we explore the extent to which dilute aluminium additions can control the size of large $Cu_{6}Sn_{5}$ hexagonal rods that can form during soldering of Sn-0.7Cu and Sn-3.0Ag-0.5Cu (SAC305) BGAs on Cu substrates. We find that Al additions cause significant grain refinement of primary $Cu_{6}Sn_{5}$ in all test samples. For example, a 0.05wt% Al addition in Sn-0.7Cu/Cu joints increased the number of primary $Cu_{6}Sn_{5}$ per $mm^{2}$ by a factor of ~7 and decreased the mean 3D length of primary $Cu_{6}Sn_{5}$ rods by a factor of ~4. The average size of $Cu_{6}Sn_{5}$ rods also decreased significantly after adding 0.05wt%Al to SAC305/Cu joints. A $Cu_{9}Al_{4}$ or $Cu_{33}Al_{17}$ particle was found near the centre of many primary $Cu_{6}Sn_{5}$ rods and reproducible crystallographic orientation relationships (ORs) were measured by electron backscatter diffraction (EBSD). The grain refinement effect after adding Al is due to the heterogeneous nucleation of $Cu_{6}Sn_{5}$ on $γ_{1}-Cu_{9}Al_{4}$ or $δ-Cu_{33}Al_{17}$ particles. The size of active nuclei was 2-5μm in Sn-4Cu-0.2Al solders, and <;1μm in Sn-0.7Cu-0.05Al/Cu and SAC305+0.05Al/Cu joints. |
| Starting Page | 2241 |
| Ending Page | 2247 |
| File Size | 2012199 |
| Page Count | 7 |
| File Format | |
| ISBN | 9781479986095 |
| DOI | 10.1109/ECTC.2015.7159915 |
| Language | English |
| Publisher | Institute of Electrical and Electronics Engineers, Inc. (IEEE) |
| Publisher Date | 2015-05-26 |
| Publisher Place | USA |
| Access Restriction | Subscribed |
| Rights Holder | Institute of Electrical and Electronics Engineers, Inc. (IEEE) |
| Subject Keyword | Joints Tin Crystals Morphology Soldering Cooling |
| Content Type | Text |
| Resource Type | Article |
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