Whisker Formation in Sn Coatings on Cu

Abstract

In the microelectronics industry, Sn is often electroplated as a protective layer on Cu conductors. Pure Sn layers on Cu develop whiskers that can cause component failures and have even been implicated in the loss of several satellites. Alloying Sn with Pb suppresses whisker formation, but the push towards Pb-free processing will make this unacceptable in the future. To understand the driving forces and mechanisms of whisker formation on pure Sn, we are measuring the kinetics of stress evolution and intermetallic formation in Sn/Cu layers. By using thin films of Sn and Cu, we can monitor the stress evolution in real time using wafer-curvature based techniques. Preliminary results of stress evolution in vapor-deposited films are presented showing the evolution of tensile stress in the Cu layers and compressive stress in the Sn layers.

This is a preview of subscription content, access via your institution.

References

  1. [1]

    H.L. Cobb, “Cadmium Whiskers”, Monthly Rev. Am. Electroplaters Soc., 33 (28): pp. 28–30 (1946).

    CAS  Google Scholar 

  2. [2]

    J. Brusse, “Tin Whiskers: Revisiting an Old Problem”, NASA's EEE Links Newsletter, 4 (4), pp. 5–7 (December 1998).

    Google Scholar 

  3. [3]

    S. Silverstein, “Reasons for Failure Lost with Galaxy 4”, Space News, pp. 3, 20 (August 17-23, 1998).

    Google Scholar 

  4. [4]

    FDA Website: “Tin Whiskers”. www.fda.gov/ora/inspect ref/itg/itg42.html

  5. [5]

    NASA Goddard Space Flight Center Tin Whisker Experimentation Page,www.nepp.nasa.gov/whisker/experiment/index.html

  6. [6]

    N.A.J. Sabbagh, H.J. McQueen, “Tin Whiskers: Causes and Remedies”, Metal Finishing, p. 27 (March 1975).

    Google Scholar 

  7. [7]

    Y.T. Cheng, A.M. Weiner, C.A. Wong, M.P. Balogh, and M.J. Lukitsch. “Stress-Induced Growth of Bismuth Nanowires”, Applied Physics Letters, 8 (17), pp. 3248–3250 (October 2002).

    Article  Google Scholar 

  8. [8]

    R.M. Fisher, L.S. Darken, and K.G. Carroll, “Accelerated Growth of Tin Whiskers”, Acta Metallurgica. 2 (3): pp. 368–372 (May 1954).

    CAS  Article  Google Scholar 

  9. [9]

    B.Z. Lee and D.N. Lee, “Spontaneous Growth Mechanism of Tin Whiskers”, Acta Metallurgica, 46 (10): pp. 3701–3714 (1998).

    CAS  Google Scholar 

  10. [10]

    K.N. Tu, “Interdiffusion and Reaction in Bimetallic Cu-Sn Thin films”, Acta Metallurgica, 21 (4): pp. 347–354 (1973).

    CAS  Article  Google Scholar 

  11. [11]

    K.N. Tu, “Irreversible Processes of Spontaneous Whisker Growth in Bimetallic Cu-Sn Thin Film Reactions”, Phys. Rev. B, 49, 2030 (1994).

    CAS  Article  Google Scholar 

  12. [12]

    J.D. Eshelby, “A Tentative Theory of Metallic Whisker Growth”, Phys. Rev., 91: pp. 755–756 (1953).

    Article  Google Scholar 

  13. [13]

    M.W. Barsoum, E.N. Hoffman, R.D. Doherty, S. Gupta, A. Zavaliangos, “Driving Force and Mechanism for Spontaneous Metal Whisker Formation”, Phys. Rev. Letters, 93 (20), (November 2004).

    Google Scholar 

  14. [14]

    Unpublished

  15. [15]

    E. Chason and J.A. Floro, “Measurements of Stress Evolution during Thin Film Growth”, Mater. Res. Symp. Proc. 428, 499 (1996).

    CAS  Article  Google Scholar 

  16. [16]

    E. Chason, L. Reinbold, S. Kumar, in preparation.

Download references

Acknowledgments

The authors appreciate helpful discussions with Gordon Barr and Ben Freund and gratefully acknowledge the support of Brown University’s Materials Research Science and Engineering Center (DMR0079964) for this research.

Author information

Affiliations

Authors

Corresponding author

Correspondence to Eric Chason.

Rights and permissions

Reprints and Permissions

About this article

Cite this article

Chason, E., Reinbold, L. & Kumar, S. Whisker Formation in Sn Coatings on Cu. MRS Online Proceedings Library 851, 316–321 (2004). https://doi.org/10.1557/PROC-851-NN5.17

Download citation