Electromigration performance of Pb-free solder joints in terms of solder composition and joining path |
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Authors: | Sun-Kyoung Seo Sung K Kang Moon Gi Cho Hyuck Mo Lee |
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Affiliation: | (1) School of Advanced Materials Science and Engineering, Sungkyunkwan University, 300 Cheoncheon-dong, Jangan-gu, Suwon, Gyeonggi-do, 440-746, Korea; |
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Abstract: | The electromigration (EM) performance of Pb-free solder joints is investigated in terms of solder composition (Sn-0.5Cu vs.
Sn-1.8Ag) and joining path to Cu vs. Ni(P) under bump metallization (UBM). In the double-sided joints of Ni(P)/solder/Cu,
the micro-structure of solder joints and the interfacial intermetallic compound (IMC) layers are significantly affected by
solder composition and joining path. The as-reflowed microstructure of Sn-0.5Cu joints consists of small columnar grains with
thin IMC layers at both UBM interfaces, independent of the joining path, while Sn-1.8Ag joints have a few large grains of
low-angle grain boundaries with thick IMC layers when joined first to Ni(P) UBM, but a few 60° twins with thin IMC layers
when joined first to Cu UBM. The EM stressing under high current densities at 150°C reveals that Sn-1.8Ag joints have a superior
lifetime compared to Sn-0.5Cu joints. In addition, the EM lifetime of Sn-1.8Ag joints reflowed first on Ni(P) UBM is the longest
among four groups of the solder joints examined. |
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