本研究旨在探討不同硼元素(B)添加量(0.0050、0.0100、0.0150 wt.%)對Sn-1.5Ag-0.7Cu (SAC157)低銀無鉛銲料微結構、疲勞性質之影響，並探討150℃熱儲存(225 hrs)前後之銲料微結構及銲點IMC層變化，以對含B銲料之抗熱性進行評估。
研究結果顯示，Sn-1.5Ag-0.7Cu-xB銲料之網狀共晶組織隨B添加量上升而變得更加緻密，共晶組織中的析出物尺寸也有細化趨勢，增強了散布強化的效果，使銲料微硬度因而提升。高溫熱儲存後，B添加量較高之銲料可保有較完整的網狀共晶組織，硬度下降量相對較少。銲點IMC層方面，IMC層之厚度有隨B添加量上升而變薄之趨勢，且IMC層在熱儲存時的成長速率亦受到B的抑制，IMC層形貌則於添加B後趨於平坦，顯示B元素有抑制IMC層成長的效果，且同時能提升銲料之抗熱性。
機械性質方面，在低週疲勞試驗中，試件之平均疲勞壽命隨B添加量增加而提升，而經由破斷面及裂紋分析發現，SAC157銲點之裂紋為延著IMC層及銲料基地之間的介面成長，斷口因而可觀察到大量裸露之 Cu6Sn5層，而隨B添加量上升，裂紋開始傾向轉往銲料內部發展，導致荷重下降速率減緩，進而增加疲勞壽命。

The purpose of this study was to investigate the effects of boron (B) addition (0.0050, 0.0100, 0.0150 wt.%) on the microstructure and fatigue properties of low-silver Sn-1.5Ag-0.7Cu (SAC157) lead-free solder. The heat resistance of the solder was also evaluated by discussing the changes in microstructure and the IMC layer after thermal storage at 150℃.
The results show that the eutectic structure of Sn-1.5Ag-0.7Cu-xB solder becomes denser, and contains finer precipitates with the increase of B content, which enhances the effect of dispersion strengthening. As a result, SAC-150B has the best performance in hardness test among all solders used in this research.
After high-temperature thermal storage, solder with a higher amount of B retains a relatively complete network of eutectic structure, and causes less decrease in hardness. The thickness of the IMC layer tends to decrease with increasing B addition, and the growth rate of the IMC layer during thermal storage is suppressed when B is added. On the other hand, it is found that the IMC layer of which without boron addition has rougher surfaces, which shows that the B element not only has an effect of suppressing the growth rate of the IMC layer, and at the same time, improves the heat resistance of the solder.
In the low cycle fatigue test, the average fatigue life of the single lap specimens increases with increasing B addition. Through failure analysis, it is found that the cracks in the SAC157 solder bumps propagate along the Cu6Sn5/solder interface. As the amount of B increases, the cracks tend to propagate stably inside the solder, resulting in a longer fatigue life of the solder bump.

[1] I. Dutta, D. Pan, R. Marks, and S. Jadhav, "Effect of thermo-mechanically induced microstructural coarsening on the evolution of creep response of SnAg-based microelectronic solders," Materials Science and Engineering: A, vol. 410, pp. 48-52, 2005.
[2] K. Kim, S. Huh, and K. Suganuma, "Effects of cooling speed on microstructure and tensile properties of Sn–Ag–Cu alloys," Materials Science and Engineering: A, vol. 333, no. 1-2, pp. 106-114, 2002.
[3] BullionByPost. Available: https://www.bullionbypost.co.uk/silver-price/
[4] London Metal Exchange. Available: https://www.lme.com/
[5] D. A. Shnawah, M. F. M. Sabri, and I. A. Badruddin, "A review on thermal cycling and drop impact reliability of SAC solder joint in portable electronic products," Microelectronics reliability, vol. 52, no. 1, pp. 90-99, 2012.
[6] H. Kim et al., "Improved drop reliability performance with lead free solders of low Ag content and their failure modes," in 2007 Proceedings 57th Electronic Components and Technology Conference, 2007, pp. 962-967: IEEE.
[7] Y. Zhang, Z. Cai, J. C. Suhling, P. Lall, and M. J. Bozack, "The effects of aging temperature on SAC solder joint material behavior and reliability," in 2008 58th Electronic Components and Technology Conference, 2008, pp. 99-112: IEEE.
[8] A. Syed, "Accumulated creep strain and energy density based thermal fatigue life prediction models for SnAgCu solder joints," in 2004 Proceedings. 54th Electronic Components and Technology Conference (IEEE Cat. No. 04CH37546), 2004, vol. 1, pp. 737-746: IEEE.
[9] Z. Cai, Y. Zhang, J. C. Suhling, P. Lall, R. W. Johnson, and M. J. Bozack, "Reduction of lead free solder aging effects using doped SAC alloys," in 2010 Proceedings 60th Electronic Components and Technology Conference (ECTC), 2010, pp. 1493-1511: IEEE.
[10] 李昭慶, "Sn-xAg-0.7Cu 無鉛銲料銲點時效影響與低週疲勞破壞之研究," 成功大學機械學系碩士論文, pp. 1-102, 2013.
[11] 汪晨暉, "Sn-xAg-0.7Cu 無鉛銲料銲點形貌與低週疲勞影響之研究," 成功大學機械工程學系碩士論文, pp. 1-91, 2014.
[12] 林育仙, "Sn-xAg-0.7Cu 無鉛銲料低週疲勞與破壞之研究," 成功大學機械工程學系碩士論文, 2015.
[13] 陳郁文, "Sn-xAg-0.7Cu 無鉛銲料銲點時效影響與低週疲勞破壞之研究," 成功大學機械工程學系碩士論文, 2016.
[14] H. Choi et al., "Improved strength of boron-doped Sn-1.0 Ag-0.5 Cu solder joints under aging conditions," Intermetallics, vol. 20, no. 1, pp. 155-159, 2012.
[15] R. D. Wang, S. M. Zhang, Q. Hu, and F. W. Zhang, "Effect of Boron on Microstructure and Properties of Sn-1.0 Ag-0.5 Cu Low-Silver Lead-Free Solder," in Materials Science Forum, 2017, vol. 898, pp. 908-916: Trans Tech Publ.
[16] 梁祐誠, "B添加對Sn-1.5Ag-0.7Cu 低銀無鉛銲料顯微組織與機械性質影響之研究," 成功大學機械工程學系碩士論文, 2018.
[17] 枋敬賀, "B添加對Sn-1.5Ag-0.7Cu-0.05Ni 低銀無鉛銲料顯微組織與機械性質影響之研究," 成功大學機械工程學系碩士論文, 2018.
[18] J. C. Suhling and P. Lall, "Electronic Packaging Applications," in Springer Handbook of Experimental Solid Mechanics, W. N. Sharpe, Ed. Boston, MA: Springer US, 2008, pp. 1015-1044.
[19] 徐祥禎, "電子構裝結構分析," 義守大學機械與自動化工程學系, pp. 1-10, 2009.
[20] L. Garner et al., "Finding Solutions to the Challenges in Package Interconnect Reliability," Intel Technology Journal, vol. 9, no. 4, 2005.
[21] E. Bradley, C. A. Handwerker, J. Bath, R. D. Parker, and R. W. Gedney, Lead-free electronics: iNEMI projects lead to successful manufacturing. John Wiley & Sons, 2007.
[22] I. Karakaya and W. Thompson, "The Ag-Sn (silver-tin) system," Bulletin of Alloy Phase Diagrams, vol. 8, no. 4, pp. 340-347, 1987.
[23] W. Yang, R. W. Messler, and L. E. Felton, "Microstructure evolution of eutectic Sn-Ag solder joints," Journal of Electronic Materials, vol. 23, no. 8, pp. 765-772, 1994.
[24] D. Yu, L. Wang, C. Wu, and C. Law, "The formation of nano-Ag3Sn particles on the intermetallic compounds during wetting reaction," Journal of Alloys and Compounds, vol. 389, no. 1-2, pp. 153-158, 2005.
[25] W. Yang, L. E. Felton, and R. W. Messler, "The effect of soldering process variables on the microstructure and mechanical properties of eutectic Sn-Ag/Cu solder joints," Journal of Electronic Materials, journal article vol. 24, no. 10, pp. 1465-1472, October 01 1995.
[26] N. Saunders and A. Miodownik, "The Cu-Sn (copper-tin) system," Bulletin of Alloy Phase Diagrams, vol. 11, no. 3, pp. 278-287, 1990.
[27] J. Xian, G. Zeng, S. Belyakov, Q. Gu, K. Nogita, and C. Gourlay, "Anisotropic thermal expansion of Ni3Sn4, Ag3Sn, Cu3Sn, Cu6Sn5 and βSn," Intermetallics, vol. 91, pp. 50-64, 2017.
[28] J. J. Sundelin, S. T. Nurmi, T. K. Lepistö, and E. O. Ristolainen, "Mechanical and microstructural properties of SnAgCu solder joints," Materials Science and Engineering: A, vol. 420, no. 1-2, pp. 55-62, 2006.
[29] P. Maitrepierre, D. Thivellier, and R. Tricot, "Influence of boron on the decomposition of austenite in low carbon alloyed steels," Metallurgical Transactions A, vol. 6, no. 2, p. 287, 1975.
[30] H. J. Jun, J. Kang, D. Seo, K. Kang, and C. Park, "Effects of deformation and boron on microstructure and continuous cooling transformation in low carbon HSLA steels," Materials Science and Engineering: A, vol. 422, no. 1-2, pp. 157-162, 2006.
[31] C. T. Liu, C. White, and J. Horton, "Effect of boron on grain-boundaries in Ni3Al," Acta metallurgica, vol. 33, no. 2, pp. 213-229, 1985.
[32] J.-F. Qu, J. Xu, Q. Hu, F.-W. Zhang, and S.-M. Zhang, "Modification of Sn–1.0 Ag–0.5 Cu solder using nickel and boron," Rare Metals, vol. 34, no. 11, pp. 783-788, 2015.
[33] J. H. Pang, B. Xiong, and T. Low, "Low cycle fatigue study of lead free 99.3 Sn–0.7 Cu solder alloy," International Journal of Fatigue, vol. 26, no. 8, pp. 865-872, 2004.
[34] C. Kanchanomai and Y. Mutoh, "Effect of temperature on isothermal low cycle fatigue properties of Sn–Ag eutectic solder," Materials Science and Engineering: A, vol. 381, no. 1-2, pp. 113-120, 2004.
[35] L. F. Coffin Jr, "A study of the effects of cyclic thermal stresses on a ductile metal," Transactions of the American Society of Mechanical Engineers, New York, vol. 76, pp. 931-950, 1954.
[36] S. Manson, "Fatigue: a complex subject—some simple approximations," Experimental mechanics, vol. 5, no. 7, pp. 193-226, 1965.
[37] H. Solomon, "Fatigue of 60/40 solder," IEEE Transactions on Components, Hybrids, and Manufacturing Technology, vol. 9, no. 4, pp. 423-432, 1986.
[38] Y. Kariya, T. Hosoi, T. Kimura, S. Terashima, M. Tanaka, and T. Suga, "Fatigue life enhancement of low silver content Sn-Ag-Cu flip-chip interconnects by Ni addition," in The Ninth Intersociety Conference on Thermal and Thermomechanical Phenomena In Electronic Systems, 2004, vol. 2, pp. 103-108: IEEE.
[39] J. H. Pang, K. H. Tan, X. Shi, and Z. Wang, "Thermal cycling aging effects on microstructural and mechanical properties of a single PBGA solder joint specimen," IEEE Transactions on Components and Packaging Technologies, vol. 24, no. 1, pp. 10-15, 2001.
[40] H. Baker and H. Okamoto, "Alloy phase diagrams," ASM handbook, vol. 3, 1992.
[41] Taiyo electric. Available: http://www.goot.jp/en/handakanren/bs-10/
[42] C. Kanchanomai, Y. Miyashita, Y. Mutoh, and S. Mannan, "Influence of frequency on low cycle fatigue behavior of Pb-free solder 96.5 Sn–3.5 Ag," Materials Science and Engineering: A, vol. 345, no. 1-2, pp. 90-98, 2003.
[43] 林欣民, "Sn-1.5Ag-0.7Cu-xB 低銀無鉛銲料微結構與機械性質之研究," 成功大學機械工程學系碩士論文, pp. 1-100, 2019.
[44] W. G. Moffatt, "The Handbook of Binary Phase Diagrams. Vol. 1-2," General Electric Co., Schenectady, N. Y. 1976,(N. P.)(Book). 1976.
[45] O. M. Abdelhadi and L. Ladani, "IMC growth of Sn-3.5 Ag/Cu system: Combined chemical reaction and diffusion mechanisms," Journal of Alloys and Compounds, vol. 537, pp. 87-99, 2012.
[46] 張宏澤, "Sb添加對Sn-1.5Ag-0.7Cu低銀無鉛銲料顯微組織與機械性質影響之研究," 成功大學機械工程學系碩士論文, pp. 1-110, 2017.
[47] 黃國禎, "低銀無鉛銲料Sn-xAg-0.7Cu銲點微結構與低週疲勞特性研究," 成功大學機械工程學系博士論文, pp. 1-101, 2016.
[48] K. Zeng, R. Stierman, T.-C. Chiu, D. Edwards, K. Ano, and K. Tu, "Kirkendall void formation in eutectic SnPb solder joints on bare Cu and its effect on joint reliability," Journal of applied physics, vol. 97, no. 2, p. 024508, 2005.
[49] J. Kim and J. Yu, "Effects of residual impurities in electroplated Cu on the Kirkendall void formation during soldering," Applied Physics Letters, vol. 92, no. 9, p. 092109, 2008.
[50] J. Yu and J. Kim, "Effects of residual S on Kirkendall void formation at Cu/Sn–3.5 Ag solder joints," Acta Materialia, vol. 56, no. 19, pp. 5514-5523, 2008.
[51] J. Görlich, G. Schmitz, and K. Tu, "On the mechanism of the binary Cu/Sn solder reaction," Applied Physics Letters, vol. 86, no. 5, p. 053106, 2005.
[52] P. Liu, P. Yao, and J. Liu, "Effects of multiple reflows on interfacial reaction and shear strength of SnAgCu and SnPb solder joints with different PCB surface finishes," Journal of Alloys and Compounds, vol. 470, no. 1-2, pp. 188-194, 2009.
[53] G. Li and B. Chen, "Formation and growth kinetics of interfacial intermetallics in Pb-free solder joint," IEEE Transactions on Components and Packaging Technologies, vol. 26, no. 3, pp. 651-658, 2003.
[54] G.-T. Lim, B.-J. Kim, K. Lee, J. Kim, Y.-C. Joo, and Y.-B. Park, "Temperature effect on intermetallic compound growth kinetics of Cu pillar/Sn bumps," Journal of electronic materials, vol. 38, no. 11, pp. 2228-2233, 2009.
[55] Y. Tang, G. Li, and Y. Pan, "Influence of TiO2 nanoparticles on IMC growth in Sn–3.0 Ag–0.5 Cu–xTiO2 solder joints in reflow process," Journal of Alloys and Compounds, vol. 554, pp. 195-203, 2013.
[56] H. Kim and K. Tu, "Kinetic analysis of the soldering reaction between eutectic SnPb alloy and Cu accompanied by ripening," Physical review B, vol. 53, no. 23, p. 16027, 1996.
[57] G. Li, B. Chen, and J. Tey, "Reaction of Sn-3.5 Ag-0.7 Cu-xSb solder with Cu metallization during reflow soldering," IEEE transactions on electronics packaging manufacturing, vol. 27, no. 1, pp. 77-85, 2004.
[58] L. Tsao, "Suppressing effect of 0.5 wt.% nano-TiO2 addition into Sn–3.5 Ag–0.5 Cu solder alloy on the intermetallic growth with Cu substrate during isothermal aging," Journal of Alloys and Compounds, vol. 509, no. 33, pp. 8441-8448, 2011.
[59] J. Shen and Y. C. Chan, "Effects of ZrO2 nanoparticles on the mechanical properties of Sn–Zn solder joints on Au/Ni/Cu pads," Journal of alloys and compounds, vol. 477, no. 1-2, pp. 552-559, 2009.
[60] S. Tay, A. Haseeb, M. R. Johan, P. Munroe, and M. Z. Quadir, "Influence of Ni nanoparticle on the morphology and growth of interfacial intermetallic compounds between Sn–3.8 Ag–0.7 Cu lead-free solder and copper substrate," Intermetallics, vol. 33, pp. 8-15, 2013.
[61] A. K. Gain, Y. C. Chan, and W. K. Yung, "Effect of additions of ZrO2 nano-particles on the microstructure and shear strength of Sn–Ag–Cu solder on Au/Ni metallized Cu pads," Microelectronics Reliability, vol. 51, no. 12, pp. 2306-2313, 2011.
[62] T. Fouzder, I. Shafiq, Y. Chan, A. Sharif, and W. K. Yung, "Influence of SrTiO3 nano-particles on the microstructure and shear strength of Sn–Ag–Cu solder on Au/Ni metallized Cu pads," Journal of Alloys and Compounds, vol. 509, no. 5, pp. 1885-1892, 2011.
[63] Z. Xia, Z. Chen, Y. Shi, N. Mu, and N. Sun, "Effect of rare earth element additions on the microstructure and mechanical properties of tin-silver-bismuth solder," Journal of Electronic Materials, journal article vol. 31, no. 6, pp. 564-567, June 01 2002.
[64] B. Chao, S.-H. Chae, X. Zhang, K.-H. Lu, J. Im, and P. S. Ho, "Investigation of diffusion and electromigration parameters for Cu–Sn intermetallic compounds in Pb-free solders using simulated annealing," Acta Materialia, vol. 55, no. 8, pp. 2805-2814, 2007.