Abstract
In this investigation on the formation of multiple-layered Kirkendall voids at Cu/Sn–3.5Ag solder joints, Sn–3.5Ag solder balls were reacted with Cu under bump metallurgy (UBM), which was electroplated using bis-sodium sulfopropyl–disulfide, C6H12O6S4Na2 (SPS) additive. The sequence of multilayer Kirkendall voids and Cu–Sn IMC (intermetallic compounds) formations are explained with the aid of cross-sectional scanning electron microscopy (SEM) micrographs and schematic diagrams. During the aging treatment at 150 °C, layers of Cu6Sn5/Cu3Sn formed at the solder joints and Kirkendall voids nucleated at the Cu3Sn/Cu interface as a result of the segregation of residual S originating from SPS. However, with Kirkendall void growth, the net section area of the Cu/Cu3Sn interface decreased and the Cu flux into Cu3Sn was inhibited. As the atomic ratio of Cu against Sn in the Cu3Sn dropped, transformation of Cu3Sn into Cu6Sn5 ensued. Subsequent diffusion of Sn atoms into the remaining Cu UBM through the remaining ligament of the Cu6Sn5/Cu interface precipitated secondary Cu3Sn beneath the primary Cu3Sn/Cu interface, and the secondary Kirkendall voids formed at the new Cu3Sn/Cu interface and so on.
Similar content being viewed by others
References
K.N. Tu, R.D. Thompson Kinetics of interfacial reaction in bimetallic CuSn thin films. Acta Metall. 30, 947 (1982)
K. Zeng, R. Stierman, T.C. Ciu, D. Edwards, K. Ano, K.N. Tu Kirkendall void formation in eutectic SnPb solder joints on bare Cu and its effect on joint reliability. J. Appl. Phys. 97, 024508 (2005)
S. Ahat, M. Sheng, L. Luo Microstructure and shear strength evolution of SnAg/Cu surface mount solder joint during aging. J. Electron. Mater. 30, 1317 (2001)
Z. Mei, M. Ahmad, M. Hu, G. Ramakrishna Kirkendall voids at Cu/solder interface and their effects on solder joint reliability Proceedings 55th Electronic Components and Technology Conference Vol. 1 (Orlando, FL 2005) 415
J.Y. Kim, J. Yu Effects of residual impurities in electroplated Cu on the Kirkendall void formation during soldering. Appl. Phys. Lett. 92, 092109 (2008)
I.E. Anderson, J.L. Harringa Suppression of void coalescence in thermal aging of tin–silver–copper-X solder joints. J. Electron. Mater. 35, 94 (2006)
M. Date, K.N. Tu, T. Shoji, M. Fujiyoshi, K. Sato Interfacial reactions and impact reliability of Sn–Zn solder joints on Cu or electroless Au/Ni(P) bond-pads. J. Mater. Res. 19, 2887 (2004)
Y.K. Jee, Y.H. Ko, J. Yu Effects of Zn addition on the drop reliability of Sn–3.5Ag–xZn/Ni(P) solder joints. J. Mater. Res. 22, 1879 (2007)
S.C. Yang, C.E. Ho, C.W. Chang, C.R. Kao Strong Zn concentration effect on the soldering reactions between Sn-based solders and Cu. J. Mater. Res. 21, 2436 (2006)
R.W. Balluffi The supersaturation and precipitation of vacancies during diffusion. Acta Metall. 2, 194 (1954)
R.W. Balluffi, L.L. Seigle Effect of grain boundaries upon pore formation and dimensional changes during diffusion. Acta Metall. 3, 170 (1955)
T.C. Chiu, K. Zeng, R. Stierman, D. Edwards, K. Ano Effect of thermal aging on board level drop reliability for Pb-free BGA packages Proceedings 54th Electronic Components and Technology Conference (Las Vegas, NV 2004) 1256
W. Yang, R.W. Messler Jr. Microstructure evolution of eutectic Sn–Ag solder joints. J. Electron. Mater 23, 765 (1994)
T. Laurila, V. Vourinen, J.K. Kivilahti Interfacial reactions between lead-free solders and common base materials. Mater. Sci. Eng., R 49, 1 (2005)
Yu. Jin, J.Y. Kim Effects of residual S on Kirkendall void formation at Cu/Sn–3.5Ag solder joints. Acta Mater 56, 5514 (2008)
J.Y. Kim, J. Yu, S.H. Kim Effects of sulphide forming element additions on the Kirkendall void formation and drop impact reliability of Cu/Sn–3.5Ag solder joints. Acta Mater 57, 5001 (2009)
C.E. Birchenall Physical Metallurgy (McGraw-Hill, New York 1959)
M. Schaffer, R.A. Fournelle, J. Liang Theory for intermetallic phase growth between Cu and liquid Sn–Pb solder based on grain boundary diffusion control. J. Electron. Mater. 27, 1167 (1998)
Z. Mei, A.J. Sunwoo, J.W. Morris Jr.: Analysis of low-temperature intermetallic growth in copper–tin diffusion couples. Metall. Trans. A 23, 857 (1992)
H.K. Kim, K.N. Tu Kinetic analysis of the soldering reaction between eutectic SnPb alloy and Cu accompanied by ripening. Phys. Rev. B 53, 16027 (1996)
J.Y. Kim, Y.C. Sohn, J. Yu Effect of Cu content on the mechanical reliability of Ni/Sn–3.5Ag system. J. Mater. Res. 22, 770 (2007)
J.Y. Song, J. Yu, T.Y. Lee Effects of reactive diffusion on stress evolution in Cu-Sn film. Scr. Mater. 51, 167 (2004)
Author information
Authors and Affiliations
Corresponding author
Rights and permissions
About this article
Cite this article
Kim, S.H., Yu, J. Secondary IMC formation induced by Kirkendall voiding in Cu/Sn-3.5Ag solder joints. Journal of Materials Research 25, 1854–1858 (2010). https://doi.org/10.1557/JMR.2010.0232
Received:
Accepted:
Published:
Issue Date:
DOI: https://doi.org/10.1557/JMR.2010.0232