Surface Morphology of Sn-Rich Solder Interconnects After Electrical Loading |
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Authors: | Q S Zhu H Y Liu Z G Wang J K Shang |
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Affiliation: | 1.Shenyang National Laboratory for Materials Science,Institute of Metal Research, Chinese Academy of Sciences,Shenyang,China;2.Department of Materials Science and Engineering,University of Illinois at Urbana-Champaign,Urbana,USA |
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Abstract: | Morphological changes from electromigration were examined on microsized Sn-Ag-Cu, pure Sn, and single-crystal Sn solder interconnects.
It was found that both grain structure and alloying had a strong influence on the form of electromigration damage. In polycrystal
Sn, grain boundary grooves were the primary form of electromigration damage, while in single-crystal Sn interconnects wavy
surface relief appeared following electromigration. Alloying with Ag and Cu encouraged formation of Sn hillocks and Cu6Sn5 intermetallic compound (IMC) segregation. The grain boundary grooves were related to the divergence of the vacancy concentration
at grain boundaries, which induced Sn grain tilting or sliding. Removal of the grain boundaries in the single-crystal interconnect
made surface diffusion the primary electromigration mechanism, resulting in wavy surface relief after long electromigration
time. In Sn-Ag-Cu alloy, directional flow of Cu caused Cu6Sn5 IMC segregation, which produced large compressive stress, driving the stressed grains to grow into hillocks. |
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