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In situ X-ray diffraction of thin electroplated Ag/Sn and Ag/In sandwich layers on Ni-coated copper substrates has been used to monitor the phase evolution in these systems at various temperatures. Initially, the course of the reactions in both systems, which are used in isothermal diffusion soldering, follows the transitions in their binary alloy phase diagrams. At 320 °C the composition of the reaction zone in the Ag/Sn case changes straightforward from tin-rich to silver-rich phases. In the case of Ag/In the same trend is observed, but the homogenization of the layer system is more complicated due to peritectic and metatectic reactions during heating up. The electroplated Ag/Sn and Ag/In ratios corresponded to the compositions of the respective ζ-phases. As the homogenization of the solder layers at 320 °C progressed, Ni–Sn and Ni–In phases were detected by EDX. The depletion of the Ag phases from Sn and In and formation of the solid solutions of Sn and In, respectively, in Ag were followed by in situ XRD. This technique allows studying the transformation of phases in thin layer sT:/PGN/ELSEVIER/META/web/00003803/ystems at process temperatures. |
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