Browsing by Author "Sweatman, K"

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    The effects of temperature and solute diffusion on volume change in Sn-Bi solder alloys
    (Springer Nature, 2022-02-02) Hao, QC; Tan, XF; Gu, QF; Sweatman, K; McDonald, SD; Nogita, K
    The different rates of thermal expansion of the many materials that make up an electronic assembly combined with temperature fluctuations are the driver of the thermal fatigue failure of solder joints. A characteristic of the Sn-Bi system, which provided the basis for many of the low process temperature solder alloys that the electronics industry is now adopting, is the very temperature-sensitive solubility of Bi and Sn in the other phase. In this study, in situ synchrotron powder x-ray diffraction was used to characterize the temperature dependence of the lattice parameters of the βSn and Bi phases in Sn-57wt%Bi and Sn-37wt%Bi. The effects of temperature and solute were separated by comparing with the data from pure βSn and pure Bi and verified using density functional theory calculations. Furthermore, the coefficients of thermal expansion of βSn and Bi during heating were also derived to reveal the thermal expansion behavior. © 2022 The Author(s) - Open access under a Creative Commons Attribution License
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    The use of variable temperature synchrotron XRD to characterise the behaviour of low temperature solder alloys
    (Australian Nuclear Science and Technology Organisation, 2021-11-26) Hao, QC; Tan, XF; Gu, QF; Sweatman, K; McDonald, SD; Nogita, K
    During the soldering process and the daily operation of the electronic devices, solder alloys experience temperature variation frequently. The mismatch in volume expansion of the solder alloys and the interconnected components can result in stresses which lead to failure. In a solder alloy system with high solubility of one element in another, the effects of thermal expansion and temperature dependent solubility limits are both important contributing factors to the thermally induced volume changes. In this study, Sn-57wt%Bi and Sn-37wt%Bi alloys which are promising materials for low-temperature solders were investigated by in-situ heating synchrotron powder X-ray diffraction (PXRD) to reveal the changes of the lattice parameters of Sn and Bi. The lattice parameters were derived by the Rietveld refinement of the PXRD patterns using TOPAS Academic V6 and following analyzed by the Coefficient of Thermal Expansion Analysis Suite (CTEAS) package using a tensor method to get the coefficient of the thermal expansion (CTE). Density functional theory (DFT) calculations were adopted to reveal the influence of the solid solution of Bi (or βSn) on the lattice parameters of βSn (or Bi), thereby decoupling the effects of thermal expansion and solid solution of Bi (or βSn) on the thermally induced volume change of βSn (or Bi). © 2021 The Authors