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Effect of electromigration on mechanical shear behavior of flip chip solder joints

Published online by Cambridge University Press:  01 March 2006

Jae-Woong Nah*
Affiliation:
Department of Materials Science and Engineering, University of California at Los Angeles, Los Angeles, California 90095-1595
Fei Ren
Affiliation:
Department of Materials Science and Engineering, University of California at Los Angeles, Los Angeles, California 90095-1595
Kyung-Wook Paik
Affiliation:
Department of Materials Science and Engineering, Korea Advanced Institute of Science and Technology, Taejon 305-701, Korea
K.N. Tu
Affiliation:
Department of Materials Science and Engineering, University of California at Los Angeles, Los Angeles, California 90095-1595
*
a) Address all correspondence to this author. e-mail: jwnah@ucla.edu
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Abstract

Effect of electromigration on mechanical shear behavior of flip chip solder joints consisting of 97Pb3Sn and 37Pb63Sn composite solder joints was studied. The under bump metallurgy (UBM) on the chip side was TiW/Cu/electroplated Cu, and the bond pad on the board side was electroless Ni/Au. It was found that the mode of shear failure has changed after electromigration and the mode depends on the direction of electron flow during electromigration. The shear induced fracture occurs in the bulkof 97Pb3Sn solder without current stressing, however, after 10 h current stressing at 2.55 × 104 A/cm2 at 140 °C, it occurs alternately at the cathode interfaces between solder and intermetallic compounds (IMCs). In the downward electron flow, from the chip to substrate, the failure site was at the Cu–Sn IMC/solder interface near the Si chip. However, in the upward electron flow, from the substrate to chip, failure occurred at the Ni–Sn IMC/solder interface near the substrate. The failure mode has a strong correlation to microstructural change in the solder joint. During the electromigration, while Pb atoms moved to the anode side in the same direction as with the electron flow, Sn atoms diffused to the cathode side, opposite the electron flow. In addition, electromigration dissolves and drives Cu or Ni atoms from UBM or bond pad at the cathode side into the solder. These reactions resulted in the large growth of Sn-based IMC at the cathode sides. Therefore, mechanical shear failure occurs predominantly at the cathode interface.

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Articles
Copyright
Copyright © Materials Research Society 2006

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References

REFERENCES

1.Lau, J.H., Pao, Y.H.: Solder Joint Reliability of BGA, CSP, Flip Chip, and Fine Pitch SMT Assembles (McGraw-Hill, New York, 1997), p. 47.Google Scholar
2.Tu, K.N.: Recent advances on electromigration in very-large-scale-integration of interconnects. J. Appl. Phys. 94, 5451 (2003).Google Scholar
3.Lee, T.Y., Tu, K.N., Kuo, S.M., Frear, D.R.: Electromigration of eutectic SnPb solder interconnects for flip chip technology. J. Appl. Phys. 89, 3189 (2001).Google Scholar
4.Lee, T.Y., Tu, K.N., Frear, D.R.: Electromigration of eutectic SnPb and SnAg3.8Cu0.7 flip chip solder bumps and under-bump metallization. J. Appl. Phys. 90, 4502 (2001).Google Scholar
5.Choi, W.J., Yeh, E.C.C., Tu, K.N.: Mean-time-to-failure study of flip chip solder joints on Cu/Ni(V)/Al thin-film under-bump-metallization. J. Appl. Phys. 94, 5665 (2003).Google Scholar
6.Nah, J.W., Paik, K.W., Suh, J.O., Tu, K.N.: Mechanism of electromigration-induced failure in the 97Pb–3Sn and 37Pb–63Sn composite solder joints. J. Appl. Phys. 94, 7560 (2003).Google Scholar
7.Hsu, Y.C., Shao, T.L., Yang, C.J., Chen, C.: Electromigration study in SnAg3.8Cu0.7 solder joints on Ti/Cr–Cu/Cu under-bump metallization. J. Electron. Mater. 32, 1222 (2003).Google Scholar
8.Shao, T.L., Lin, K.C., Chen, C.: Electromigration studies of flip chip Sn95/Sb5 solder bumps Cr/Cr–Cu/Cu under-bump metallization. J. Electron. Mater. 32, 1278 (2003).Google Scholar
9.Shao, T.L., Chiu, S.H., Chen, C., Yao, D.J., Hsu, C.Y.: Thermal gradient in solder joints under electrical-current stressing. J. Electron. Mater. 33, 1350 (2004).Google Scholar
10.Shao, T.L., Chen, Y.H., Chiu, S.H., Chen, C.: Electromigration failure mechanisms for SnAg3.5 solder bumps on Ti/Cr–Cu/Cu under-bump metallization pads. J. Appl. Phys. 96, 4518 (2004).Google Scholar
11.Lin, Y.H., Tsai, C.M., Hu, Y.C., Lin, Y.L., Kao, C.R.: Electromigration-induced failure in flip-chip solder joints. J. Electron. Mater. 34, 27 (2005).Google Scholar
12.Lin, Y.H., Hu, Y.C., Tsai, C.M., Kao, C.R., Tu, K.N.: In situ observation of the void formation-and-propagation mechanism in solder joints under current-stressing. Acta Mater. 53, 2029 (2005).Google Scholar
13.Liu, Y.H., Lin, K.L.: Damages and microstructural variation of high-lead and eutectic SbPb composite flip chip solder bumps induced by electromigration. J. Mater. Res. 20, 2184 (2005).Google Scholar
14.Nah, J.W., Suh, J.O., Tu, K.N.: Effect of current crowding and Joule heating on electromigration-induced failure in flip chip composite solder joints tested at room temperature. J. Appl. Phys. 98, 013715 (2005).Google Scholar
15.Ren, F., Nah, J.W., Gan, H., Suh, J.O., Tu, K.N., Xiong, B., Xu, L., Pang, J. Effect of electromigration on mechanical behavior of solder joints, in Materials, Technology and Reliability of Advanced Interconnects—2005, edited by Besser, P.R., McKerrow, A.J., Iacopi, F., Wong, C.P., and Vlassak, J. (Mater. Res. Soc. Symp. Proc. 863 Warrendale, PA, 2005), B10.2.Google Scholar
16.Mercado, L.L., Sarihan, V., Guo, Y., Mawer, A.: Impact of solder pad size on solder joint reliability in flip chip PBGA packages. IEEE Trans. Adv. Packag. 23, 416 (2000).Google Scholar
17.Pang, J.H.L., Chong, D.Y.R., Low, T.H.: Thermal cycling analysis of flip-chip solder joint reliability. IEEE Trans. Compon. Packag. Technol. 24, 705 (2001).Google Scholar
18.Kariya, Y., Hosoi, T., Terashima, S., Tanaka, M., Otsuka, M.: Effect of silver content on the shear fatigue properties of Sn–Ag–Cu flip-chip interconnects. J. Electron. Mater. 33, 321 (2004).Google Scholar
19.Nagesh, V.K., Peddada, R., Ramalingam, S., Sur, B., Tai, A. Challenges of flip chip on organic substrate assembly technology, in Proc. 49th Electronic Components and Technology Conference (IEEE, Piscataway, NJ, 1999), p. 975.Google Scholar
20.Shukla, R., Murali, V., Bhansali, A. Flip chip CPU package technology at Intel: A technology and manufacturing overview, in Proc. 49th Electronic Components and Technology Conference (IEEE, Piscataway, NJ, 1999), p. 945.Google Scholar
21.Guo, Y., Kuo, S.M., Zhang, C.: Reliability evaluations of under bump metallurgy in two solder systems. IEEE Trans. Compon. Packag. Technol. 24, 655 (2001).Google Scholar
22.Yeh, E.C.C., Choi, W.J., Tu, K.N., Elenius, P., Balkan, H.: Current-crowding-induced electromigration failure in flip chip solder joints. Appl. Phys. Lett. 80, 580 (2002).Google Scholar