Abstract
The thermal reliability of Sn-3Ag-0.5Cu/Au/Pd(P)/Cu solder joints was evaluated in this study. After reflow and subsequent solid-state aging (180°C), the reaction product species at the interface included Cu6Sn5 [or (Cu,Pd)6Sn5] and Cu3Sn, and their growth was strongly dependent on the Pd(P) thickness, δ Pd(P). As δ Pd(P) increased, the growth of Cu6Sn5 was significantly enhanced, while that of Cu3Sn was suppressed. Computer coupling of phase diagrams and thermochemistry (CALPHAD) analysis showed that minor incorporation of Pd (~2 at.%) into the Cu6Sn5 phase decreased the Gibbs free energy of Cu6Sn5 from −7339 J/mol to −9191 J/mol. This effect might enhance Sn diffusion in Cu6Sn5 but diminish Cu diffusion in Cu3Sn, thereby facilitating the growth of Cu6Sn5 but retarding that of Cu3Sn. High-speed ball shear (HSBS) test results showed that the mechanical properties of the solder joints were slightly enhanced by an increase in δ Pd(P). These findings suggest that direct deposition of Au/Pd(P) bilayers over the Cu pads can effectively modify the mechanical reliability of solder joints.
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Ho, C., Kuo, T., Gierlotka, W. et al. Development and Evaluation of Direct Deposition of Au/Pd(P) Bilayers over Cu Pads in Soldering Applications. J. Electron. Mater. 41, 3276–3283 (2012). https://doi.org/10.1007/s11664-012-2200-9
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DOI: https://doi.org/10.1007/s11664-012-2200-9