Journal of Electronic Materials

, Volume 41, Issue 2, pp 262–272

In Situ Synchrotron Characterization of Melting, Dissolution, and Resolidification in Lead-Free Solders


  • Bite Zhou
    • Michigan State University
    • Michigan State University
  • Guilin Wu
    • Max-Planck-Institut für Eisenforschung GmbH
  • Stefan Zaefferer
    • Max-Planck-Institut für Eisenforschung GmbH
  • Tae-Kyu Lee
    • Cisco Systems, Inc.
  • Kuo-Chuan Liu
    • Cisco Systems, Inc.

DOI: 10.1007/s11664-011-1785-8

Cite this article as:
Zhou, B., Bieler, T.R., Wu, G. et al. Journal of Elec Materi (2012) 41: 262. doi:10.1007/s11664-011-1785-8


Melting and solidification of SAC 305 lead-free solder joints in a wafer-level chip-scale package were examined in situ with synchrotron x-ray diffraction. The chips with balls attached (but not assembled to a circuit board) were reflowed one to three times using a temperature and time history similar to an industrial reflow process. Diffraction patterns from the same joint were collected every 0.5 s during the melting and solidification process. The solidification of the Sn phase in the solder joint occurred between 0.5 s and 1 s. During melting, most of the Sn melted in about 0.5 s, but in some cases took 2–5 s for the Sn peak to completely disappear. In one instance, the Sn peak persisted for 30 s. The Ag3Sn peaks dissolved in about 1–2 s, but the Cu6Sn5 peaks from the interface were persistent and did not change throughout the melting and solidification process. Completely different Sn crystal orientations were always developed upon resolidification.


Lead-free solderWLCSPsynchrotron x-ray diffractionreflowSn crystal orientation

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© TMS 2011