本研究係觀察錫鋅銲錫合金薄帶於通電狀態下之富鋅相微結構變化，首先以臨場X光繞射分析各電流密度通電下(2000~8000A/cm2)之富鋅相的晶格變化，於各電流密度下積分強度皆先急遽上升而後下降，在電流密度高於6000A/cm2時，積分強度下降最為嚴重，下降至0，晶格遭受嚴重破壞，而通電瞬間Zn(002)的應變量即超過0.2%，應變值在電流密度8000A/cm2甚至高達0.5%，表示電子風擾動晶格結構之能量非常大，使通電中之晶格承受高應變，以TEM分析計算，發現鋅晶粒內部的差排密度會高達1018m-2，高於傳統金屬在冷加工後的差排密度二到三個數量級，顯示大量電子風重擊使得晶面被嚴重扭曲並且產生大量差排。而後以造成晶格嚴重變化之電流密度(8000A/cm2)施予薄帶通電，觀察通電後之富鋅相的微結構變化，其中明顯發現有富鋅相溶解之行為，本研究歸類為三種機制:晶界溶解機制(Grain boundary dissolution)、異向性溶解機制(Anisotropic dissolution)、六方表面溶解機制(Hexagonal surface dissolution)，此三種機制都與晶界、次晶粒晶界有關，晶界處有大量差排存在，此處的原子排列相對於晶粒內部較不規則，能量相對較高，原子容易移動，故孔洞首先會在晶界處成核，而三種機制之行為差異可能是受於本身晶粒取向或晶粒間取相所影響。通電使富鋅相溶解進入錫基地相中，通電初期各區域鋅濃度增加但差異不大，持續通電後陽極端除了此區富鋅相溶解外，也有從陰極端電遷移之通量，而使鋅濃度高於陰極端，電流導致富鋅相溶解，使錫基地相呈現鋅過飽和現象，鋅之濃度可達4~5wt%。

This present study investigated the microstructure variation of Zn-rich phase induced by electric current stressing. The in-situ XRD (X-ray Diffraction) investigation was performed to analyze the variation of lattice structure under the current stressing. The intensity of the diffraction peak of Zn (002) increased initially and then decreased gradually. It revealed that the lattices were destructed severely. It was also noticed that the diffraction peak shifts towards lower angle, which can be attributed to the formation of dislocation and thus strain induced by current stressing. The dissolution behavior was further investigated with SEM (Scanning Electron Microscope) and FIB (Focus Ion Beam) of the specimen quenched with liquid nitrogen after current stressing. This study concluded three mechanisms of dissolution: grain boundary dissolution, anisotropic dissolution, and hexagonal surface dissolution. All of the dissolution mechanisms were related to the grain or phase boundary, but the three mechanisms may be different due to the orientation of grains themselves or influences by neighboring grains. The Sn-Zn phase diagram indicates that Sn and Zn exhibit nearly zero mutual solubility. However, Zn was found to exhibit certain solubility in the Sn matrix of Sn9Zn solder under current stressing within 6000~8000A/cm2. The Zn concentration increases from 2.2 wt% of as-received specimen to 3~8 wt% after current stressing. This study provides a good understanding to the dissolution of second phase of solder alloy under current stressing.

[1] Y. C. Chan and D. Yang, "Failure mechanisms of solder interconnects under current stressing in advanced electronic packages," Progress in Materials Science, vol. 55, pp. 428-475, 2010.
[2] C. S. Hau-Riege, "An introduction to Cu electromigration," Microelectronics Reliability, vol. 44, pp. 195-205, 2004.
[3] J. P. Dekker, C. A. Volkert, E. Arzt and P. Gumbsch "Alloying Effects on Electromigration Mass Transport," Physical Review Letters, vol. 87, pp. 035901-1~035901-4, 2001.
[4] X. Zhu, H. Kotadia, S. Xu, H. Lu, S. H. Mannan, C. Bailey and Y. C. Chan, "Electromigration in Sn–Ag solder thin films under high current density," Thin Solid Films, vol. 565, pp. 193-201, 2014.
[5] C. M. Chen, Y. M. Hung, C. P. Lin and W. C. Su, "Effect of temperature on microstructural changes of the Sn-9wt.%Zn lead-free solder stripe under current stressing," Materials Chemistry and Physics, vol. 115, pp. 367-370, 2009.
[6] W. Yue, H. B. Qin, M. B. Zhou, X. Ma and X. P. Zhang, "Electromigration induced microstructure evolution and damage in asymmetric Cu/Sn-58Bi/Cu solder interconnect under current stressing," Transactions of Nonferrous Metals Society of China, vol. 24, pp. 1619-1628, 2014.
[7] Q. T. Huynh, C. Y. Liu, C. Chen and K. N. Tu, "Electromigration in eutectic SnPb solder lines," Journal of applied physics, vol. 89, pp. 4332-4335, 2001.
[8] E. C. C. Yeh, W. J. Choi, K. N. Tu, P. Elenius and H. Balkan, "Current-crowding-induced electromigration failure in flip chip solder joints," Applied Physics Letters, vol. 80, pp. 580-582, 2002.
[9] Y. S. Lai and C. L. Kao, "Electrothermal coupling analysis of current crowding and Joule heating in flip-chip packages," Microelectronics Reliability, vol. 46, pp. 1357-1368, 2006.
[10] A. Lodder, "The driving force in electromigration," Physica A: Statistical Mechanics and its Applications, vol. 158, pp. 723-739, 1989.
[11] Y. D. Lu, X. Q. He, Y. F. En, X. Wang and Z. Q. Zhuang, "Polarity effect of electromigration on intermetallic compound formation in SnPb solder joints," Acta Materialia, vol. 57, pp. 2560-2566, 2009.
[12] X. F. Zhang, J. D. Guo and J. K. Shang, "Reverse polarity effect from effective charge disparity during electromigration in eutectic Sn–Zn solder interconnect," Journal of Materials Research, vol. 23, pp. 3370-3378, 2008.
[13] J. Shi and H. B. Huntington, "Electromigration of gold and silver in single crystal tin," Journal of Physics and Chemistry of Solids, vol. 48, pp. 693-696, 1987.
[14] F. Y. Ouyang, K. N. Tu and Y. S. Lai, "Effect of electromigration induced joule heating and strain on microstructural recrystallization in eutectic SnPb flip chip solder joints," Materials Chemistry and Physics, vol. 136, pp. 210-218, 2012.
[15] Q. L. Yang and J. K. Shang, "Interfacial segregation of Bi during current stressing of Sn-Bi/Cu solder interconnect," Journal of Electronic Materials, vol. 34, pp. 1363-1367, 2005.
[16] J. Daghfal and J. K. Shang, "Current-Induced Phase Partitioning in Eutectic Indium-Tin Pb-Free Solder Interconnect," Journal of Electronic Materials, vol. 36, pp. 1372-1377, 2007.
[17] Y. T. Chiu, K. L. Lin and Y. S. Lai, "Orientation transformation of Pb grains in 5Sn–95Pb/63Sn–37Pb composite flip-chip solder joints during electromigration test," Journal of Materials Research, vol. 23, pp. 1877-1881, 2008.
[18] A. T. Wu, A. M. Gusak, K. N. Tu and C. R. Kao, "Electromigration-induced grain rotation in anisotropic conducting beta tin," Applied Physics Letters, vol. 86, pp. 241902-1~241902-3, 2005.
[19] G. Zhao and F. Yang, "Effect of DC current on tensile creep of pure tin," Materials Science and Engineering: A, vol. 591, pp. 97-104, 2014.
[20] L. Van de Voorde, B. Vekemans, E. Verhaeven, P. Tack, R. D. Wolf, J. Garrevoet, P. Vandenabeele and L. Vincze, "Analytical characterization of a new mobile X-ray fluorescence and X-ray diffraction instrument combined with a pigment identification case study," Spectrochimica Acta Part B: Atomic Spectroscopy, vol. 110, pp. 14-19, 2015.
[21] A. S. Budiman, "6 - The evolution of microstructure in copper interconnects during electromigration," Electromigration in Thin Films and Electronic Devices, Woodhead Publishing, pp. 135-189, 2011.
[22] J. Y. He, K. L. Lin and A. T. Wu, "The diminishing of crystal structure of Sn9Zn alloy due to electrical current stressing," Journal of Alloys and Compounds, vol. 619, pp. 372-377, 2015.
[23] C. N. Liao, K. C. Chen, W. W. Wu and L. J. Chen, "In situ transmission electron microscope observations of electromigration in copper lines at room temperature," Applied Physics Letters, vol. 87, pp. 141903-1~141903-3, 2005.
[24] Y. T. Chiu, C. H. Liu, K. L. Lin and Y. S. Lai, "Supersaturation induced by current stressing," Scripta Materialia, vol. 65, pp. 615-617, 2011.
[25] Y. T. Chiu, K. L. Lin and Y. S. Lai, "Dissolution of Sn in a SnPb solder bump under current stressing," Journal of Applied Physics, vol. 111, pp. 043517-1~043517-8, 2012.
[26] W. Y. Chen, T. C. Chiu, K. L. Lin, A. T. Wu, W. L. Jang, C. L. Dong and H. Y. Lee, "Anisotropic dissolution behavior of the second phase in SnCu solder alloys under current stress," Scripta Materialia, vol. 68, pp. 317-320, 2013.
[27] H. Radamson and L. Thylén, "Chapter 4 - Moore’s Law for Photonics and Electronics," Monolithic Nanoscale Photonics–Electronics Integration in Silicon and Other Group IV Elements, Oxford: Academic Press, pp. 121-150, 2015.
[28] M. L. Huang, Q. Zhou, N. Zhao, and Z. J. Zhang, "Abnormal Diffusion Behavior of Zn in Cu/Sn-9 wt.%Zn/Cu Interconnects During Liquid–Solid Electromigration," Journal of Electronic Materials, vol. 42, pp. 2975-2982, 2013.
[29] M. Tomita and T. G. M. Van De Ven, "Calculation of diffraction angles in ordered latices," Journal of Colloid and Interface Science, vol. 100, pp. 112-115, 1984.
[30] S. R. Stock and B. D. Cullity," Elements of X-ray Diffraction, 3rd ed., Prentice Hall, p. 441, 2001.
[31] T. J. Lardner and R. R. Archer," Mechanics of Solids: An Introduction, McGraw-Hill, p. 60, 1994.
[32] S. Mrowec and S. Marcinkiewicz," Defects and diffusion in solids:
an introduction, Elsevier Amsterdam, pp. 277-279, 1980.
[33] F. C. Porter," Zinc handbook: properties, processing, and use in design, CRC Press, p. 45, 1991.
[34] W. D. Callister and D. G. Rethwisch," Fundamentals of materials science and engineering: an integrated approach: John Wiley & Sons, pp. 265-266, 2012.
[35] D. T. Castro, R. J. O. M. Hoofman, J. Michelon, D. J. Gravesteijn and C. Bruynseraede," Void growth modeling upon electromigration stressing in narrow copper lines," Journal of Applied Physics, vol. 102, pp. 123515-1~123515-12, 2007.
[36] C. L. Gan and M. K. Lim, "5 - Voiding in copper interconnects during electromigration," Electromigration in Thin Films and Electronic Devices, Woodhead Publishing, pp. 113-134, 2011.
[37] 黃漢婕, "錫3.5銀銲錫合金通電中微結構變化之研究, 國立成功大學碩士論文, p. 39, 民國103年.
[38] W. D. Callister and D. G. Rethwisch," Fundamentals of materials science and engineering: an integrated approach, John Wiley & Sons, p.177, 2012.
[39] S. Wang, Z. Zhu, and M. Starink," Estimation of dislocation densities in cold rolled Al‐Mg‐Cu‐Mn alloys by combination of yield strength data, EBSD and strength models," Journal of microscopy, vol. 217, pp. 174-178, 2005
[40] C. C. Chung, S. W. Wang, Y. C. Chen, C. P. Ju and J. H. C. Lin, "Effect of cold rolling on structure and tensile properties of cast Ti–7.5Mo alloy," Materials Science and Engineering: A, vol. 631, pp. 52-66, 2015.
[41] C. E. Ho, C. H. Yang, and L. H. Hsu, "Electromigration in thin-film solder joints," Surface and Coatings Technology, vol. 259, Part B, pp. 257-261, 2014.
[42] F. Abd El-Salam, A. M. Abd El-Khalek and R. H. Nada, "Study of the structural and mechanical properties of Sn–8.6wt.%Zn alloys using creep measurements," Materials Science and Engineering: A, vol. 460-461, pp. 14-19, 2007.
[43] P. S. Ho and T. Kwok, "Electromigration in metals," Reports on Progress in Physics, vol. 52, pp. 301-348, 1989.
[44] S. Kumar, M. T. Alam, Z. Connell and M. A. Haque, "Electromigration stress induced deformation mechanisms in free-standing platinum thin films," Scripta Materialia, vol. 65, pp. 277-280, 2011.
[45] I. A. Blech, "Electromigration in thin aluminum films on titanium nitride," Journal of Applied Physics, vol. 47, pp. 1203-1208, 1976.