掺杂对电子封装无铅互连界面微结构和可靠性影响的机理研究
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摘要
电子封装无铅化的进展很快,世界各国的研究者已开发出不同的可替代铅锡合金的无铅合金系,其中Sn-Ag、Sn-Cu以及Sn-Ag-Cu合金被认为最有希望替代铅锡合金。但目前的研究结果表明它们只能在某些性能上达到或超过铅锡合金,其综合性能上仍不能媲美铅锡合金,且随着微电子产品的持续小型化,这些无铅合金的某些弱点逐渐显露并限制着无铅焊点可靠性的提高。因此,目前尚没有一种合金焊料能满足现代电子封装超微化发展所要求的各项性能。因此研发高可靠性无铅焊料和研究影响无铅互连可靠性的关键问题是高密度微电子封装的重要课题。
该项目在Sn3.0Ag0.5Cu焊料中掺入锑、稀土钇以及稀土化合物LaB6。实验结果表明,添加锑可以显著改善焊料的润湿性能,使焊料与铜的接触角减小8o;微量的稀土元素(低于0.1wt%)也能够有效地改善焊料的润湿性能。同时,稀土能够细化合金中的金属间化合物晶粒,能提高焊点的机械性能。Sb具有抑制界面化合物生长的作用,但是同时加入Sb与稀土Y的焊料中,其界面化合物的生长却是比只含Sb而不含Y的焊点的界面化合物生长快。可能的原因是Sb与Y反应生成Sb-Y化合物,抑制了Sb发挥作用。Sn3.0Ag0.5Cu焊料掺入0.4wt%的锑或0.1wt% LaB6时的实验结果表明:在润湿反应时间少于700s时,其界面化合物的厚度与时间成线性或抛物线关系,其中Sn3.0Ag0.5Cu 0.4Sb0.10LaB6/Cu界面处的Cu6Sn5层生长速度最慢,其对阻碍界面原子的互扩散能力应是最强的;固态反应阶段,根据各种老化温度下界面互扩散系数的比较,得出界面化合物层的生长快慢排序如下:
Sn3.0Ag0.5Cu0.4Sb0.10LaB6/Cu 计算了各种界面的Cu-Sn化合物的激活能,结果表明:Sn3.0Ag0.5Cu/Cu界面Cu-Sn化合物的激活能最高,为92.79kJ,其次是Sn3.0Ag0.5Cu0.4Sb0.10LaB6/Cu和Sn3.0Ag 0.5Cu0.10LaB6/Cu,分别是85.14kJ和84.91kJ,而Sn3.0Ag0.5Cu0.4Sb /Cu界面的Cu-Sn化合物激活能最小,只有75.57kJ。综合考虑各界面互扩散系数随温度变化情况,发现在老化温度范围以内(≤190℃), Sn3.0Ag0.5Cu0.4Sb 0.10aB6/Cu的扩散系数都是最小的,因而其界面化合物的生长速率最慢。
With increasing concerns on environmental protection and human being health, lead-free solders have been increasingly used to replace the Pb-containing solders in the field of microelectronic packaging. Many different lead-free solder alloy systems, such as Sn-Ag, Sn-Ag-Cu, Sn-Cu, Sn-Ag-Bi, have been developed and are currently being used as promising alternatives to the Sn-Pb solders. However,the comprehensive properties of all the existing lead-free solders are not as well as that of the Sn37Pb solder. Among the varieties of lead-free solders, the Sn-Ag-Cu family is regarded as the most promising candidate for replacement of Sn-Pb solders, because it has superior mechanical properties of strength, elongation, creep, and fatigue resistance than Sn-Pb solders.As the trendence of high density packaging goes on, the size of each I/O decreases so as to supply more input/output (I/O) for a constant packaging area. In this case, the reliability problems caused by the over growth of intermetallic compound (IMC, of brittle property) in Sn-Ag-Cu solder joints due to their higher reflow temperature must be solved.
In the present research, Sb、rare earth yttrium and LaB6 were added to the Sn3.0Ag0.5Cu solder paste. It is found that Sn3.0Ag0.5Cu0.8SbXY, with X ranging between 0.05 and 0.1, has the best wettability on Cu substrate. The growth rate of IMC increases as the amount of yttrium increase from 0wt% to 0.25wt% in the Sn3.0Ag0.5Cu0.8SbXY/Cu system during aging.When the yttrium concentration is increased from 0.25wt% to 0.5wt%, the IMC thickness decreases. Further increase in the RE concentration just results in a slightly increasement of the IMC thickness. The possible reason for this result is that Sb reacts with Y to form Sb-Y compounds and finally the effect of Sb on the growth of IMC weakens. Secondly,0.4wt% Sb and/or 0.1wt% LaB6 were added to the same solder paste used in the firet step and let all the four kinds of solder joints to go through the multi-reflowed and aging process. IMC growth during reflow process was studied and compared their growth rate during the aging process. Results show that solder joints with 0.4wt% Sb and 0.1wt% LaB6 has the minmum interdiffusion coefficient among the four kinds of solder joints in our experimential temperature range. In addition, the activation energy of the Cu-Sn compound was calculated. It is found that the Cu-Sn compound of the Sn3.0Ag0.5Cu/Cu solder joint has the maximum activation energy of 92.79kJ. The other three activation energys are 75.57 kJ, 84.91kJ, 85.14kJ for Sn3.0Ag0.5Cu0.4Sb/Cu, Sn3.0Ag0.5Cu0.10LaB6/Cu and Sn3.0Ag0.5Cu 0.4Sb0.10LaB6/Cu respectively. Although the Sn3.0Ag0.5Cu/Cu has the maximum activation energy, the activation energy of Sn3.0Ag0.5Cu0.4Sb0.10LaB6/Cu just lower down a little bit.With a much more less diffusion constant D0, it has the minmum interdiffusion coefficient in the experimental range.
该项目在Sn3.0Ag0.5Cu焊料中掺入锑、稀土钇以及稀土化合物LaB6。实验结果表明,添加锑可以显著改善焊料的润湿性能,使焊料与铜的接触角减小8o;微量的稀土元素(低于0.1wt%)也能够有效地改善焊料的润湿性能。同时,稀土能够细化合金中的金属间化合物晶粒,能提高焊点的机械性能。Sb具有抑制界面化合物生长的作用,但是同时加入Sb与稀土Y的焊料中,其界面化合物的生长却是比只含Sb而不含Y的焊点的界面化合物生长快。可能的原因是Sb与Y反应生成Sb-Y化合物,抑制了Sb发挥作用。Sn3.0Ag0.5Cu焊料掺入0.4wt%的锑或0.1wt% LaB6时的实验结果表明:在润湿反应时间少于700s时,其界面化合物的厚度与时间成线性或抛物线关系,其中Sn3.0Ag0.5Cu 0.4Sb0.10LaB6/Cu界面处的Cu6Sn5层生长速度最慢,其对阻碍界面原子的互扩散能力应是最强的;固态反应阶段,根据各种老化温度下界面互扩散系数的比较,得出界面化合物层的生长快慢排序如下:
Sn3.0Ag0.5Cu0.4Sb0.10LaB6/Cu
With increasing concerns on environmental protection and human being health, lead-free solders have been increasingly used to replace the Pb-containing solders in the field of microelectronic packaging. Many different lead-free solder alloy systems, such as Sn-Ag, Sn-Ag-Cu, Sn-Cu, Sn-Ag-Bi, have been developed and are currently being used as promising alternatives to the Sn-Pb solders. However,the comprehensive properties of all the existing lead-free solders are not as well as that of the Sn37Pb solder. Among the varieties of lead-free solders, the Sn-Ag-Cu family is regarded as the most promising candidate for replacement of Sn-Pb solders, because it has superior mechanical properties of strength, elongation, creep, and fatigue resistance than Sn-Pb solders.As the trendence of high density packaging goes on, the size of each I/O decreases so as to supply more input/output (I/O) for a constant packaging area. In this case, the reliability problems caused by the over growth of intermetallic compound (IMC, of brittle property) in Sn-Ag-Cu solder joints due to their higher reflow temperature must be solved.
In the present research, Sb、rare earth yttrium and LaB6 were added to the Sn3.0Ag0.5Cu solder paste. It is found that Sn3.0Ag0.5Cu0.8SbXY, with X ranging between 0.05 and 0.1, has the best wettability on Cu substrate. The growth rate of IMC increases as the amount of yttrium increase from 0wt% to 0.25wt% in the Sn3.0Ag0.5Cu0.8SbXY/Cu system during aging.When the yttrium concentration is increased from 0.25wt% to 0.5wt%, the IMC thickness decreases. Further increase in the RE concentration just results in a slightly increasement of the IMC thickness. The possible reason for this result is that Sb reacts with Y to form Sb-Y compounds and finally the effect of Sb on the growth of IMC weakens. Secondly,0.4wt% Sb and/or 0.1wt% LaB6 were added to the same solder paste used in the firet step and let all the four kinds of solder joints to go through the multi-reflowed and aging process. IMC growth during reflow process was studied and compared their growth rate during the aging process. Results show that solder joints with 0.4wt% Sb and 0.1wt% LaB6 has the minmum interdiffusion coefficient among the four kinds of solder joints in our experimential temperature range. In addition, the activation energy of the Cu-Sn compound was calculated. It is found that the Cu-Sn compound of the Sn3.0Ag0.5Cu/Cu solder joint has the maximum activation energy of 92.79kJ. The other three activation energys are 75.57 kJ, 84.91kJ, 85.14kJ for Sn3.0Ag0.5Cu0.4Sb/Cu, Sn3.0Ag0.5Cu0.10LaB6/Cu and Sn3.0Ag0.5Cu 0.4Sb0.10LaB6/Cu respectively. Although the Sn3.0Ag0.5Cu/Cu has the maximum activation energy, the activation energy of Sn3.0Ag0.5Cu0.4Sb0.10LaB6/Cu just lower down a little bit.With a much more less diffusion constant D0, it has the minmum interdiffusion coefficient in the experimental range.
引文
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[3] YANG YU, ZHIDONG XIA, FU GUO,and YAOWU SHI, Effects of Rare-Earth Addition on Properties and Microstructure of Lead-Free Solder Balls, Journal of ELECTRONIC MATERIALS, Vol. 37, No. 7, pp975-981,2008.
[4] CHANG DONG ZOU, YU LAI GAO, BIN YANG, XIN ZHI XIA, QI JIE ZHAI, CRISTINA ANDERSSON, and JOHAN LIU, Nanoparticles of the Lead-free Solder Alloy Sn-3.0Ag-0.5Cu with Large Melting Temperature Depression, Journal of ELECTRONIC MATERIALS, Vol. 38, No. 2, pp351-355,2009.
[5]邹长东,应用纳米尺寸效应降低Sn基无铅焊料熔化温度的基础研究,上海大学工学博士学位论文, 2010.5.
[6] Hongjin Jiang, Kyoung-sik Moon, Fay Hua, and C. P. Wong, Synthesis and Thermal and Wetting Properties of Tin/Silver Alloy Nanoparticles for Low Melting Point Lead-Free Solders, Chem. Mater., Vol. 19, No. 18, pp4482-4485,2007.
[7] Hongjin Jiang, Kyoung-sik Moon, C. P. Wong, Tin/Silver/Copper Alloy Nanoparticle Pastes for Low Temperature Lead-free Interconnect Applications, 2008 Electronic Components and Technology Conference, pp1400-1404.
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[9] Jeong-Won Yoon, Seung-Boo Jung, Effect of immersion Ag surface finish on interfacial reaction and mechanical reliability of Sn–3.5Ag–0.7Cu solder joint, Journal of Alloys and Compounds 458 (2008) 200–207.
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[15] S.-W.CHEN, C.-N.CHIU and K.-C.HSIEH, Phase Equilibria of the Sn-Ag-Cu-Ni Quaternary System at 210℃, Journal of ELECTRONIC MATERIALS, Vol. 36, No. 3, 2007.
[16] Han-Byul Kang, Jee-Hwan Bae, Jae-Wook Lee, Min-Ho Park, Young-Chul Lee, Jeong-Won Yoon, Seung-Boo Jung and Cheol-Woong Yang, Control of interfacial reaction layers formed in Sn–3.5Ag–0.7Cu/electroless Ni–P solder joints, 2008 Acta Materialia Inc. Published by Elsevier Ltd.
[17] MENG Gong-ge, T.Takemoto, H. Nishikawa, Correlations between IMC thickness and three factors in Sn-3Ag-0.5Cu alloy system, Trans. Nonferrous Met. SOC, China 17 (2007), 686-690.
[18] P. Yao, P. Liu, J. Liu, Interfacial Reaction and Shear Strength of SnAgCu-xNi/Ni Solder Joints during Aging at 150℃, Microelectronic Engineering (2008), doi: 10.1016/j.mee.2008.12.013.
[19] Y.W.Wang, Y.W.Lin, C.R.Kao, Kirkendall voids formation in the reaction between Ni-doped SnAg lead-free solders and different Cu substrates, Microelectron Reliab (2008), 2008.09.010.
[20] Jung-Sub Lee, Kun-Mo Chu, Rainer Patzelt, Dionysios Manessis, Andreas Ostman, Duk Young Jeon. Effects of Co addition in eutectic Sn–3.5Ag solder on shear strength and microstructural development. Microelectronic Engineering 85 (2008) 1577–1583.
[21] Sheng Lu, Baohua Wang, Jing Chen, Evolutions in Microstructure and Property of Sn-Ag-Cu Lead-free Solders with Trace Addition of agnesium, 2007 9th Electronics Packaging Technology Conference.
[22] Sheng Lu, Baohua Wang, Chenggang Wei, Jing Chen, Weijun Wang, Melting Temperature and Physical Properties of Sn-Ag-Cu-Mg Lead-Free Solders Based on Uniform Design, 2007 IEEE.
[23] Sheng LU, Fei LUO, Jing CHEN, Baohua WANG, Microstructural and physical characteristics of Sn-Ag-Cu-Mg Lead-free Solders, 2008 International Conference on Electronic Packaging Technology & High Density Packaging (ICEPT-HDP 2008).
[24]芦笙,卫成刚,王凤云,刘寿松, Sn-Ag-Cu-Mg无铅钎料的组织与性能,材料开发与应用. 2005年12月.
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[26] G. Y. Li, B.L. Chen and J. N. Tey, Reaction of Sn-3.5Ag-0.7Cu-xSb solder with Cu metallization during reflow soldering, IEEE Trans.On EPM, USA, vol.27, no.1, pp.77-85, 2004.
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[2] WEIMINXIAO, YAOWU SHI, YONGPING LEI, ZHIDONG XIA, and FU GUO, Comparative Study of Microstructures and Properties of Three Valuable SnAgCuRE Lead-Free Solder Alloys, Journal of ELECTRONIC MATERIALS, Vol. 35, No. 5, pp1095-1103, 2006.
[3] YANG YU, ZHIDONG XIA, FU GUO,and YAOWU SHI, Effects of Rare-Earth Addition on Properties and Microstructure of Lead-Free Solder Balls, Journal of ELECTRONIC MATERIALS, Vol. 37, No. 7, pp975-981,2008.
[4] CHANG DONG ZOU, YU LAI GAO, BIN YANG, XIN ZHI XIA, QI JIE ZHAI, CRISTINA ANDERSSON, and JOHAN LIU, Nanoparticles of the Lead-free Solder Alloy Sn-3.0Ag-0.5Cu with Large Melting Temperature Depression, Journal of ELECTRONIC MATERIALS, Vol. 38, No. 2, pp351-355,2009.
[5]邹长东,应用纳米尺寸效应降低Sn基无铅焊料熔化温度的基础研究,上海大学工学博士学位论文, 2010.5.
[6] Hongjin Jiang, Kyoung-sik Moon, Fay Hua, and C. P. Wong, Synthesis and Thermal and Wetting Properties of Tin/Silver Alloy Nanoparticles for Low Melting Point Lead-Free Solders, Chem. Mater., Vol. 19, No. 18, pp4482-4485,2007.
[7] Hongjin Jiang, Kyoung-sik Moon, C. P. Wong, Tin/Silver/Copper Alloy Nanoparticle Pastes for Low Temperature Lead-free Interconnect Applications, 2008 Electronic Components and Technology Conference, pp1400-1404.
[8] Kelvin Pun, Poh Leng Eu, M.N. Islam, C Q Cuil, Effect of Ni Layer Thickness on Intermetallic Formation and Mechanical Strength of Sn-Ag-Cu Solder Joint, 2008 10th Electronics Packaging Technology Conference, pp487-493.
[9] Jeong-Won Yoon, Seung-Boo Jung, Effect of immersion Ag surface finish on interfacial reaction and mechanical reliability of Sn–3.5Ag–0.7Cu solder joint, Journal of Alloys and Compounds 458 (2008) 200–207.
[10] W. Peng et al, Effect of thermal aging on the interfacial structure of SnAgCu solder joints on Cu, Microelectronics Reliability vol 47, 2007 pp2161–2168.
[11] J.-W. Yoon et al, Effects of isothermal aging and temperature–humidity treatment of substrate on joint reliability of Sn–3.0Ag–0.5Cu/OSP-finished Cu CSP solder joint, Microelectronics Reliability 48 (2008) pp1864–1874.
[12] P. Arulvanan et al, Effects of process conditions on reliability, microstructure evolution and failure modes of SnAgCu solder joints, Microelectronics Reliability 46 (2006) 432–439.
[13] A. Ourdjini, M.A. Azmah Hanim, S.F. Joyce Koh, I Siti Aisha, KS.Tan, and Y. T. Chin, Effect of Solder Volume on Interfacial Reactions between Eutectic Sn-Pb and Sn-Ag-Cu Solders and Ni(P)-Au Surface Finish, International Electronic Manufacturing Technology, Putrajaya,Malaysia,2006.
[14] Lihua Qi, Jihua Huang, Jiangang Zhang, Ye Wang, Microstructure and Intermetallic Growth at the Sn-Ag-Cu/Ni Interface after Thermal-shearing Cycling, 2005 6th International Conference on Electronic Packaging Technology.
[15] S.-W.CHEN, C.-N.CHIU and K.-C.HSIEH, Phase Equilibria of the Sn-Ag-Cu-Ni Quaternary System at 210℃, Journal of ELECTRONIC MATERIALS, Vol. 36, No. 3, 2007.
[16] Han-Byul Kang, Jee-Hwan Bae, Jae-Wook Lee, Min-Ho Park, Young-Chul Lee, Jeong-Won Yoon, Seung-Boo Jung and Cheol-Woong Yang, Control of interfacial reaction layers formed in Sn–3.5Ag–0.7Cu/electroless Ni–P solder joints, 2008 Acta Materialia Inc. Published by Elsevier Ltd.
[17] MENG Gong-ge, T.Takemoto, H. Nishikawa, Correlations between IMC thickness and three factors in Sn-3Ag-0.5Cu alloy system, Trans. Nonferrous Met. SOC, China 17 (2007), 686-690.
[18] P. Yao, P. Liu, J. Liu, Interfacial Reaction and Shear Strength of SnAgCu-xNi/Ni Solder Joints during Aging at 150℃, Microelectronic Engineering (2008), doi: 10.1016/j.mee.2008.12.013.
[19] Y.W.Wang, Y.W.Lin, C.R.Kao, Kirkendall voids formation in the reaction between Ni-doped SnAg lead-free solders and different Cu substrates, Microelectron Reliab (2008), 2008.09.010.
[20] Jung-Sub Lee, Kun-Mo Chu, Rainer Patzelt, Dionysios Manessis, Andreas Ostman, Duk Young Jeon. Effects of Co addition in eutectic Sn–3.5Ag solder on shear strength and microstructural development. Microelectronic Engineering 85 (2008) 1577–1583.
[21] Sheng Lu, Baohua Wang, Jing Chen, Evolutions in Microstructure and Property of Sn-Ag-Cu Lead-free Solders with Trace Addition of agnesium, 2007 9th Electronics Packaging Technology Conference.
[22] Sheng Lu, Baohua Wang, Chenggang Wei, Jing Chen, Weijun Wang, Melting Temperature and Physical Properties of Sn-Ag-Cu-Mg Lead-Free Solders Based on Uniform Design, 2007 IEEE.
[23] Sheng LU, Fei LUO, Jing CHEN, Baohua WANG, Microstructural and physical characteristics of Sn-Ag-Cu-Mg Lead-free Solders, 2008 International Conference on Electronic Packaging Technology & High Density Packaging (ICEPT-HDP 2008).
[24]芦笙,卫成刚,王凤云,刘寿松, Sn-Ag-Cu-Mg无铅钎料的组织与性能,材料开发与应用. 2005年12月.
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