The solder joint microstructures of immersion Ag with Sn-xZn (x = 0 wt.%, 1 wt.%, 5 wt.%, and 9 wt.%) solders were analyzed and correlated with their drop impact reliability. Addition of 1 wt.% Zn to Sn did not change the interface microstructure and was only marginally effective. In comparison, the addition of 5 wt.% or 9 wt.% Zn formed layers of AgZn3/Ag5Zn8 at the solder joint interface, which increased drop reliability significantly. Under extensive aging, Ag-Zn intermetallic compounds (IMCs) transformed into Cu5Zn8 and Ag3Sn, and the drop impact resistance at the solder joints deteriorated up to a point. The beneficial role of Zn on immersion Ag pads was ascribed to the formation of Ag-Zn IMC layers, which were fairly resistant to the drop impact, and to the suppression of the brittle Cu6Sn5 phase at the joint interface.
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This work was supported by the office of KAIST EEWS Initiative (EEWS: Energy, Environment, Water, and Sustainability) (Grant No. EEWS0917).
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Jee, Y.K., Yu, J. Interfacial Reactions and Joint Strengths of Sn-xZn Solders with Immersion Ag UBM. J. Electron. Mater. 39, 2286–2291 (2010). https://doi.org/10.1007/s11664-010-1308-z
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DOI: https://doi.org/10.1007/s11664-010-1308-z