Abstract
This article reports a comparative study of the formation and growth of intermetallic phases at the interface of Cu wetted with a thick solder joint or a thin, pretinned solder layer. The η phase (Cu6Sn5) forms when Cu is wet with eutectic solder at temperatures below 400 °C. The intermetallic layer is essentially unaffected by aging at 70 °C for as long as 13 weeks. On aging a eutectic joint at 170 °C, the η-phase intermetallic layer thickens and ε phase (Cu3Sn) nucleates at the Cu/intermetallic interface and grows to a thickness comparable to that of the η phase, while a Pb-rich boundary layer forms in the solder. The aging behavior of a thin, pretinned eutectic layer is qualitatively different. At 170 °C, the Sn in the eutectic is rapidly consumed to form η-phase intermetallic, which converts to ε phase. The residual Pb withdraws into isolated islands, and the solderability of the surface deteriorates. When the pretinned layer is Pb-rich (95Pb-5Sn), the Sn in the layer is also rapidly converted into η phase, in the form of dendrites penetrating from the intermetallic at the Cu interface and discrete precipitates in the bulk. How ever, the development of the intermetallic largely ceases when the Sn is consumed; ε phase does not form, and the residual Pb remains as an essentially continuous layer, preserving the solderability of the sample. These observations are interpreted in light of the Cu-Sn and Pb-Sn phase diagrams, the temperature of initial wetting, and the relative diffusivities of Cu and Sn in the solder and intermetallic phases.
Similar content being viewed by others
References
E.K. Ohriner:Weld. J., 1987, vol. 66, pp. 191s-202s.
L. Zakraysek:Weld. J., 1971, vol. 36, pp. 522s-527s.
L. Zakraysek:Weld. J., 1972, vol. 37, pp. 536s-541s.
M.E. Warwick and S.J. Muckett:Circuit World, 1983, vol. 9, pp. 5–11.
T. Farrell:Met. Sci., 1976, vol. 3, pp. 87–93.
ba]D.A. Unsworth and C.A. Mackay:Trans. Inst. Met. Finish, 1973, vol. 51, pp. 85–90.
K. Kumar and A. Moscaritolo:J. Electrochem. Soc: Solid-State Sci. Technol., 1981, vol. 128, pp. 379–83.
A.J. Sunwoo, H. Hayashigatani, J.W. Morris, Jr., and G.K. Lucey, Jr.:J. Met., 1991, vol. 43, pp. 21–24.
J.O.G. Parent, D.D.L. Chung, and I.M. Bernstein:J. Mater. Sci., 1988, vol. 23, pp. 2564–72.
Y.A. Chang:INCRA Monograph, 1979, vol. 6, pp. 631–42.
W. Hofmann:Lead and Lead Alloys—Properties and Technology, Springer-Verlag, New York, NY, 1970, pp. 149–53.
V.C. Marcotte and K. Schroder:MRS Symp., 1983, vol. 19, pp. 403–10.
I. Okamoto and T. Yasuda:Trans. JWRI, 1986, vol. 15, pp. 73–80.
D.J. Chakrabarti and D.E. Laughlin:Bull. Alloy Phase Diagram, 1984, vol. 5, pp. 503–10.
N. Saunders and A.P. Miodownik:Bull. Alloy Phase Diagrams, 1990, vol. 11, pp. 278–87.
A. Gangulee, G.C. Das, and M.B. Bever:Metall. Trans., 1973, vol. 4, pp. 2063–66.
P.L. Brooks and E. Gillan:Acta Metall., 1970, vol. 18, pp. 1181–85.
Y. Watanabe, Y. Fujinaga, and H. Iwasaki:Acta Crystallogr., 1983, vol. 39, pp. 306–11.
D. Frear, D. Grivas, and J.W. Morris, Jr.:J. Elect. Mater., 1988, vol. 17, p. 171.
D. Grivas, D. Frear, L.K. Quan, and J.W. Morris, Jr.:J. Elect. Mater., 1986, vol. 15, pp. 355–59.
K.N. Tu:Acta Metall., 1973, vol. 21, pp. 347–54.
K.N. Tu and R.D. Thompson:Acta Metall., 1982, vol. 30, pp. 947–52.
Z. Lubyova, P. Fellner, and K. Mutiasovsky:Z. Metallkd., 1975, vol. 66, pp. 179–85.
Z. Mei, A. Sunwoo, and J.W. Morris, Jr.:Metall. Trans. A, 1992, vol. 23A, pp. 857–64.
M. Onishi and H. Fujibuchi:Trans. Jpn. Inst. Met., 1975, vol. 16, pp. 539–47.
H.B. Huntington, C.-K. Hu, and S.N. Mei:Diffusion in Solids: Recent Developments Conf. Proc, M.A. Dayananda and G.E. Murch, eds., TMS-AIME, Warrendale, PA, 1984, pp. 97–119.
L. Quan, D. Frear, D. Grivas, and J.W. Morris, Jr.:J. Elect. Mater., 1987, vol. 16, p. 203.
D. Frear, D. Grivas, and J.W. Morris, Jr.:J. Elect. Mater., 1987, vol. 16, pp. 181–86.
J. London and D.W. Ashall:Brazing & Soldering, Autumn, 1986, pp. 49–55.
Author information
Authors and Affiliations
Additional information
A.J. SUNWOO, Formerly with the Lawrence Berkeley Laboratory, Berkeley, CA,
Rights and permissions
About this article
Cite this article
Sunwoo, A.J., Morris, J.W. & Lucey, G.K. The growth of Cu-Sn intermetallics at a pretinned copper-solder interface. Metall Trans A 23, 1323–1332 (1992). https://doi.org/10.1007/BF02665064
Received:
Published:
Issue Date:
DOI: https://doi.org/10.1007/BF02665064