Abstract
Surface and thin film techniques reveal an immediate and intense surface reaction during wetting of Sn-3.3Ag-4.8Bi solder paste to Ni-Au board finishes. Rutherford backscattering spectroscopy (RBS) shows that a typical, vendorsupplied Ni-Au board finish consists of ∼750 Å of Au above the Ni. Stylus profilometry indicates that the finish surface is rough with average vertical height variations of ∼1–2 µm. The board finish seen by the solder alloy during wetting contains a large ∼45% atom fraction of adventitious surface C observed by Auger spectroscopy (AES). The AES and energy-dispersive x-ray spectroscopy (EDX) indicates that Ni has fully intermixed throughout the alloy within seconds of wetting. Dissolution of the Au cap layer into the alloy and Bi and Ag surface segregation is observed. Auger point analysis and maps at the leading edge of the wetting front show no evidence of flux advance ahead of the alloy. Bismuth does not move out with the spreading wetting front. A unique feature of this work is the acquisition of real-time, in-situ electron microscopic observations of the spreading Sn-3.3Ag-4.8Bi alloy front across the Ni-Au substrate during wetting. The observations have been recorded on videotape and converted into computer files accessible on the World Wide Web with standard media players (ftp://131.204.44.20).
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S.V. Sattiraju, B. Dang, R.W. Johnson, Y. Li, J.S. Smith, and M.J. Bozack, IEEE Trans. Electron. Packaging Manufacturing 25, 168 (2002).
J.S. Hwang, Environment-Friendly Electronics: Lead-Free Technology (Electrochemical Publications Ltd., Isle of Man, British Isles, 2001), p. 224.
J.S. Hwang, Environment-Friendly Electronics: Lead-Free Technology (Electrochemical Publications Ltd., Isle of Man, British Isles, 2001), p. 225.
N. Lee, Chip Scale Rev., p. 42 (2000).
Lead-Free Solder Project Final Report, NCMS Report No. 170502, National Center for Manufacturing Sciences, Ann Arbor, MI, 1997.
Lead-Free, High-Temperature, Fatigue-Resistant Solder Final Report, NCMS Report No. 0096RE01, National Center for Manufacturing Sciences, Ann Arbor, MI, 2001.
M.J. Bozack, A.E. Bell, and L.W. Swanson, J. Phys. Chem. 92, 3925 (1988).
M.J. Bozack, L.W. Swanson, and A.E. Bell, J. Mater. Sci. 22, 2421 (1987).
M.J. Bozack, W.J. Choyke, J.N. Russell, Jr., L. Muehlhoff, and J.T. Yates, Jr., J. Vac. Sci. Technol. A 5, 1 (1987).
K.W. Bryant and M.J. Bozack, J. Vac. Sci. Technol. A 17, 3057 (1999).
V. Smentkowski and J.T. Yates, Jr., J. Vac. Sci. Technol. A 11, 3002 (1993).
D.A. Gedcke, L.G. Byars, and W.H. Hardy, Scanning Electron Microsc. III, 981 (1982).
Rutherford Universal Manipulation Program, http://www.genplot.com/doc/rump.htm.
R.W. Johnson and M.J. Bozack, to be published.
To access and download: Open a standard browser, such as Microsoft Internet Explorer. In the site address line, type ftp://131.204.44.20. The files are named Sn-3.3Ag-4.8Bi (paste) to Ni-Au, T1.mpg and Sn-3.3Ag-4.8Bi (paste) to Ni-Au,T2.mpg. Although the files are large (∼150 MB), average download time is a few minutes on most current desktop computers with Ethernet connections.
In recent work on 1206 chip resistors, we find Sn-3.3Ag-4.8Bi solder joints to be substantially less reliable than eutectic Sn-37Pb joints over a temperature cycling range from −40°C to 150°C.
K. Kanaya and S. Okayama, J. Phys. D. Appl. Phys. 5, 43 (1972).
See, for example, the front cover of the classic text The Mechanics of Solder Alloy Wetting and Spreading, eds. F.G. Yost, F.M. Hosking, and D.R. Frear (New York: Van Nostrand Reinhold, 1993).
M.J. Bozack, R.W. Johnson, and S. Gale, to be published.
M.J. Bozack, J. Electron. Mater., submitted for publication.
S.V. Sattiraju, B. Dang, R.W. Johnson, Y. Li, J.S. Smith, and M.J. Bozack, IEEE Trans. Electron. Packaging Manufacturing 25, 168 (2002).
W.K. Choi and H.M. Lee, J. Electron. Mater. 28, 1251 (1999).
S. Bader, W. Gust, and H. Hieber, Acta Mater. 43, 329 (1995).
S.V. Sattiraju, B. Dang, R.W. Johnson, Y. Li, J.S. Smith, and M.J. Bozack, IEEE Trans. Electron. Packaging Manufacturing, 25, 168 (2002).
Ibid..
F.H. Reid and W. Goldie, Gold Plating Technology (Palo Alto, CA: Electrochemical Publications Ltd., Palo Alto, CA, 1974), p. 226.
J. Glazer, P.A. Kramer, and J.W. Morris, Jr., Surface Mount Int., Proc. Techn. Progr., p. 629 (1991).
A.M. Minor and J.W. Morris, Jr., J. Electron. Mater. 29, 1170 (2000).
We have also observed this phenomenon in our laboratory. Results will be reported in a future publication.
C.H. Zhong, S. Yi, Y.C. Mui, C.P. Howe, D. Olsen, and W.T. Chen, Electronic Components and Technology Conf. (Piscataway, NJ: IEEE, 2000), p. 151.
M.J. Bozack and P.R. Davis, Mater. Sci. Eng. A150, 255 (1992).
Z. Guo, A.F. Sprecker, M. Kim, and H. Conrad, Proc. ASM 4th Electronic Materials and Process Congr., Montreal, Canada, Fall 1991, (ASM, Pittsburgh, PA, 1991), p. 155.
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Bozack, M.J., Johnson, R.W. Real-time scanning electron microscopy and auger spectroscopy of wetting in Sn-3.3Ag-4.8Bi solder paste wetted to Ni-Au. J. Electron. Mater. 34, 248–265 (2005). https://doi.org/10.1007/s11664-005-0211-5
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DOI: https://doi.org/10.1007/s11664-005-0211-5