The creep properties of tin-based, lead-free solders, Sn-3.0Ag-0.5Cu and Sn-7.5Zn-3.0Bi, were investigated for the temperature range from 298 K to 398 K. The creep rupture time decreases with increasing initial stress and temperature. The Omega method is applied to the analysis of the solder creep curves. The creep rate \( \dot{\varepsilon} \) is expressed by the following formula: \(\ln \dot{\varepsilon} =\ln \dot{\varepsilon_0} + \Omega \varepsilon \), where \( \dot{\varepsilon_0} \) and Ω are experimentally determined. The parameter \( \dot{\varepsilon_0} \), the imaginary initial strain rate, increases with increasing initial stress and temperature. The parameter Ω is temperature dependent, but less dependent on the initial stress. The apparent activation energy for \( \dot{\varepsilon_0} \) is 108 kJ/mol in Sn-3.0Ag-0.5Cu and 83 kJ/mol in Sn-7.5Zn-3.0Bi. These values are close to the activation energy for the lattice diffusion of tin. The creep rupture time is calculated using the parameters \(\dot{\varepsilon_0} \) and Ω. The calculated creep rupture time is in good agreement with the measured creep rupture time.
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Acknowledgements
The help of Mr. T. Matsuda from Sumitomo Metal Technology Inc. in acquiring solder mechanical properties and many helpful discussions with Mr. E. Mukai, Research Center, DENKA, are gratefully acknowledged.
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Monden, K. Creep Life Assessment of Tin-Based Lead-Free Solders Based on Imaginary Initial Strain Rate. J. Electron. Mater. 36, 1691–1696 (2007). https://doi.org/10.1007/s11664-007-0285-3
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DOI: https://doi.org/10.1007/s11664-007-0285-3