Undercooling and microhardness of Pb-free solders on various under bump metallurgies

Abstract

The undercooling behavior of pure Sn, Sn–0.7Cu, Sn–3.5Ag, and Sn–3.8Ag–0.7Cu solder alloys was observed in terms of various under bump metallurgies (UBMs). Four different UBMs (electroplated Cu, electroplated Ni, electroless Ni(P), and electroless Ni(P)/immersion Au) were used. The amount of the undercooling of Pb-free solder alloys was reduced when reacted with electroplated Cu UBM and Ni-based UBMs. The Ni-based UBMs were more effective than Cu UBM in reducing the undercooling of Pb-free solders. When Ni3Sn4 was formed during the interfacial reactions with Ni-based UBMs, the reduction of undercooling was significant, especially for pure Sn and Sn–3.5Ag. The effects of UBMs on the undercooing of Pb-free solder alloys are discussed by comparing intermetallic compounds formed during interfacial reactions with UBMs. In addition, the microstructural changes as well as the microhardness of four solders with or without UBMs are discussed, which could be related to their undercooling behaviors.

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

FIG. 1
TABLE I
FIG. 2
FIG. 3
FIG. 4
FIG. 5

References

  1. 1

    J. Bath, C. Handwerker E. Bradley: Research update: Lead-free solder alternatives. Circuits Assem. 11, 31 2000

    Google Scholar 

  2. 2

    I.E. Anderson, J.C. Foley, B.A. Cook, J. Harringa, R.K. Terpatra O. Unal: Alloying effects in near-eutectic Sn–Ag–Cu solder alloys for improved microstructural stability. J. Electron. Mater. 30, 1050 2001

    CAS  Article  Google Scholar 

  3. 3

    K.J. Puttlitz: Sn–Ag and Sn–Ag–X solders and properties in Handbook of Lead-Free Solder Technology for Microelectronic Assemblies edited by K.J. Puttlitz and K.A. Stalter Marcel Dekker New York 2004 239–280

    Google Scholar 

  4. 4

    S.W. Jeong, J.H. Kim H.M. Lee: Effect of cooling rate on growth of IMC and fracture mode of near-eutectic Sn–Ag–Cu/Cu pad: Before and after aging. J. Electron. Mater. 33, 1530 2004

    CAS  Article  Google Scholar 

  5. 5

    S.K. Kang, P. Lauro, D-Y. Shih, D.W. Henderson K.J. Puttlitz: The microstructure, solidification, mechanical properties, and thermal fatigue behavior of lead (Pb)-free solders and solder joints used in microelectronic applications. IBM J. Res. Dev. 49, 606 2005

    Article  Google Scholar 

  6. 6

    B. Vonnegut: Variation with temperature of the nucleation rate of supercooled liquid tin and water drops. J. Colloid Sci. 3, 563 1948

    CAS  Article  Google Scholar 

  7. 7

    G.M. Pound V.K.L.A. Mer: Kinetics of crystalline nucleus formation in supercooled liquid tin. J. Am. Chem. Soc. 74, 2323 1952

    CAS  Article  Google Scholar 

  8. 8

    S.K. Kang, W.K. Choi, D-Y. Shih, D.W. Henderson, T. Gosselin, A. Sarkhel, C. Goldsmith K.J. Puttlitz: Formation of Ag3Sn plates in Sn–Ag–Cu alloys and optimization of their alloy composition in Proc. 53rd Electronic Components and Technology Conference IEEE Piscataway, NJ 2003 64–70

  9. 9

    L.P. Lehman, R.K. Kinyanjui, L. Zavalij, A. Zribi E.J. Cotts: Growth and selection of intermetallic species in Sn–Ag–Cu no-Pb solder systems based on pad metallurgies and thermal histories in Proc. 53rd Electronic Components and Technology Conference IEEE Piscataway, NJ 2003 1215–1221

  10. 10

    S.K. Kang, D-Y. Shih, D. Leonard, D.W. Henderson, T. Gosselin, S-I. Cho, J. Yu W.K. Choi: Controlling Ag3Sn plate formation in near-ternary-eutectic Sn–Ag–Cu solder by minor Zn alloying. JOM 56(6), 34 2004

    CAS  Article  Google Scholar 

  11. 11

    R. Kinyanjui, L.P. Lehman, L. Zavalij E. Cotts: Effect of sample size on the solidification temperature and microstructure of SnAgCu near eutectic alloys. J. Mater. Res. 20, 2914 2005

    CAS  Article  Google Scholar 

  12. 12

    S.K. Kang, M.G. Cho, P. Lauro D-Y. Shih: Critical factors affecting the undercooling of Pb-free, flip-chip solder solder bumps and in-situ observation of solidification process in Proc. 57th Electronic Components and Technology Conference IEEE Piscataway, NJ 2007 1597–1603

  13. 13

    S.K. Kang, M.G. Cho, P. Lauro D-Y. Shih: Study of the undercooling of Pb-free, flip-chip solder bumps and in situ observation of solidification process. J. Mater. Res. 22, 557 2007

    CAS  Article  Google Scholar 

  14. 14

    Q. Xiao, L. Nguyen W.D. Armstrong: The anomalous microstructural, tensile, and aging response of thin-cast Sn3.9Ag0.6Cu lead-free solder. J. Electron. Mater. 34, 617 2005

    CAS  Article  Google Scholar 

  15. 15

    K.S. Kim, S.H. Huh K. Suganuma: Effects of fourth alloying additive on microstructures and tensile properties of Sn–Ag–Cu alloy and joints with Cu. Microelectron. Reliab. 43, 259 2002

    Article  Google Scholar 

  16. 16

    I. de Sousa, D.W. Henderson, L. Party, S.K. Kang D-Y. Shih: The influence of low level doping on the thermal evolution of SAC alloy solder joints with Cu pad structures in Proc. 56th Electronic Components and Technology Conference IEEE Piscataway, NJ 2006 1454–1461

  17. 17

    S-W. Chen C-C. Huang: The relationship between the peak shape of a DTA curve and the shape of a phase diagram. Chem. Eng. Sci. 50, 417 1995

    CAS  Article  Google Scholar 

  18. 18

    S-W. Chen, C-C. Lin C-M. Chen: Determination of the melting and solidification characteristics of solders using differential scanning calorimetry. Metall. Mater. Trans. A 29, 1965 1998

    Article  Google Scholar 

  19. 19

    Y-D. Jeon, S. Nieland, A. Ostmann, H. Reichl K-W. Paik: A study on interfacial reactions between electroless Ni–P under bump metallization and 95.5Sn–4.0Ag–0.5Cu alloy. J. Electron. Mater. 32, 548 2003

    CAS  Article  Google Scholar 

  20. 20

    M.G. Cho, K.W. Paik, H.M. Lee, S.W. Booh T.G. Kim: Interfacial reaction between 42Sn–58Bi solder and electroless Ni–P/immersion Au under bump metallurgy during aging. J. Electron. Mater. 35, 35 2006

    CAS  Article  Google Scholar 

  21. 21

    C.E. Ho, S.C. Yang C.R. Kao: Interfacial reaction issues for lead-free electronic solders. J. Mater. Sci. Mater. Electron. 18, 155 2007

    CAS  Article  Google Scholar 

  22. 22

    S-W. Chen C-H. Wang: Interfacial reactions of Sn–Cu/Ni couples at 250 °C. J. Mater. Res. 21, 2270 2006

    CAS  Article  Google Scholar 

Download references

Acknowledgments

We gratefully acknowledge Dr. Hae Jin Kim and Dr. Jin Bae Lee at the Korea Basic Science Institute (KBSI) for their work on DSC measurements as well as Han-Na Park at KBSI for the SEM observation and EDS analysis.

Author information

Affiliations

Authors

Corresponding author

Correspondence to Hyuck Mo Lee.

Rights and permissions

Reprints and Permissions

About this article

Cite this article

Cho, M.G., Kang, S.K. & Lee, H.M. Undercooling and microhardness of Pb-free solders on various under bump metallurgies. Journal of Materials Research 23, 1147–1154 (2008). https://doi.org/10.1557/jmr.2008.0133

Download citation