材料选择对BGA焊点热可靠性影响的有限元仿真研究
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摘要
伴随着电子工业的发展,电子封装作为一门独立的新型高技术行业迅速成长起来。表面贴装技术(Surface Mount Technology,简称; SMT)作为电子封装的一项技术突破,被誉为“电子封装技术革命”,它具有诸多优越性。但也存在着致命的弱点--焊点寿命有限、可靠性较差。尤其是低周热疲劳作为其主要失效因素得到广泛的关注。然而由于焊点尺寸细小,现有的实验手段无法在热疲劳试验的同时实时监测焊点的内部应力应变。于是,利用有限元模型的方法进行分析,成为当前最可行的方法。
不同材料的选择会对最终焊点的应力集中、应力应变分布变化以及焊点的寿命产生直接的影响,然而目前国内外对该方向还没有研究。本文针对这一空白开展课题,研究了不同材料选择下BGA(Ball Grid Array)焊点阵列的可靠性。
研究通过ANSYS软件,采用统一粘塑性Anand本构方程,首次建立了基于BGA焊点形态的三维焊点阵列可靠性分析有限元模型,进行了焊点力学性能分析,得出了交变热循环作用下,不同基板材料搭配组别Sn60Pb40钎料焊点在各个时刻的应力应变分布特点以及其随热循环温度改变的变化规律。进一步根据最危险焊点最薄弱环节应变数据,采用修正的Coffin-Manson方程预测了不同基板材料搭配下焊点阵列的疲劳寿命。塑料封装与FR4基板组合时焊点的寿命,是陶瓷封装与FR4基板组合寿命的7倍。若Si芯片贴装于FR4基板上,则其焊点寿命相当短。Si芯片贴装于陶瓷基板可以很好的取代它,既可以提高组装密度,焊点寿命也比前者提高了6倍。陶瓷封装对陶瓷基板搭配是其中可靠性最好的,它的焊点寿命最长。综上所述,组装上下基板材料的热匹配性越好,焊点的热循环寿命越高。
最后采用同样的方法,对陶瓷封装与FR4基板组合下无铅钎料-Sn96.5Ag3.5焊点的热循环应力应变进行了仿真研究,并与同条件下的SnPb钎料-Sn60Pb40结果进行了对比,结果显示无铅钎料大大地提高了焊点的热可靠性,热疲劳寿命是同样情况下SnPb钎料寿命的4倍以上。
所有这些研究为今后电子封装不同适用下的材料选择提供了借鉴,具有重要的实际指导意义。
With the development of electronic industry, electronic packaging grows up rapidly as an independent new high-tech calling. Among all the technology options, surface mounted technology (SMT) is the fastest expanding one which was thought as “A Revolution of the Electronic Packaging”. However, some of the disadvantages of SM connectors, such as inadequate availability and its less reliable solder joints, are also existing instead of many advantages of SM connectors. Generally, the low-cycle fatigue induced by thermal cycle is the major concern in the reliability of SMT .Due to the fine-small solder joint dimension, existing experiment measures can’t be used to monitor the stress and strain of solder inner, when thermal fatigue experiment is processing. So, the finite element model analysis is the most feasible means.
Different choice of material has a direct influence on final centralized stress, stress-strain distribution--change and life of solder joints. However international and domestic studies aren’t yet toward this direction at present. This text launches the subject to this blank to research in the reliability of the solder joint of BGA (Ball Grid Array ) under different material choice.
For the first time, the geometrical model for mechanical analysis of the solder joint is built directly from three-dimensional shape model of the BGA by ANSYS software. An unified viscoplastic constitutive law, the Anand model is applied to represent the inelastic deformation behavior for Sn60Pb40 solder. The mechanical performance is analyzed using finite element method .The distribution characteristics of stress and strain in solder joint are given at every time of thermal cycle. Besides, the variety rule of stress and strain with thermal cycle is acquired. Moreover, based on the strain data of the weakest site of the most dangerous solder ball in the array, fatigue life of thermally loaded BGA solder joints is predicted using the modificative coffin-Masson equation and reliability of the solder joints with different top-bottom material assembly is compared. Results indicate: The material heat matching of top-bottom base plate is more better, the life of assembly is more longer. The life-span of the solder joints assembled with ceramic encapsulation and FR4 base plate is 7 times than the one while adopting plastic encapsulation and FR4 base plate to make up; when sticking the Si chip to the FR4 base plate, the life-span is quite shortened; sticking the Si chip to the ceramic base plate can replace the former, because it not only raise the density of assembling, but also life-span of solder joints is prolonged to 6 times than the former; It is the compounding of ceramic to ceramic that match bestly.
Finally, by the same way, adopting the existing mechanical capability data of lead-free solder analyses its thermal reliability in contrast with the one of Sn60Pb40 solder under the ceramic-FR4 material compounding. Results show lead-free solder increases the reliability greatly. Its thermal fatigue life is 4 times than the one of SnPb solder.
The conclusion will provide a direction on material choice of electronic packaging in order to suit to different reliable requirement in future.
不同材料的选择会对最终焊点的应力集中、应力应变分布变化以及焊点的寿命产生直接的影响,然而目前国内外对该方向还没有研究。本文针对这一空白开展课题,研究了不同材料选择下BGA(Ball Grid Array)焊点阵列的可靠性。
研究通过ANSYS软件,采用统一粘塑性Anand本构方程,首次建立了基于BGA焊点形态的三维焊点阵列可靠性分析有限元模型,进行了焊点力学性能分析,得出了交变热循环作用下,不同基板材料搭配组别Sn60Pb40钎料焊点在各个时刻的应力应变分布特点以及其随热循环温度改变的变化规律。进一步根据最危险焊点最薄弱环节应变数据,采用修正的Coffin-Manson方程预测了不同基板材料搭配下焊点阵列的疲劳寿命。塑料封装与FR4基板组合时焊点的寿命,是陶瓷封装与FR4基板组合寿命的7倍。若Si芯片贴装于FR4基板上,则其焊点寿命相当短。Si芯片贴装于陶瓷基板可以很好的取代它,既可以提高组装密度,焊点寿命也比前者提高了6倍。陶瓷封装对陶瓷基板搭配是其中可靠性最好的,它的焊点寿命最长。综上所述,组装上下基板材料的热匹配性越好,焊点的热循环寿命越高。
最后采用同样的方法,对陶瓷封装与FR4基板组合下无铅钎料-Sn96.5Ag3.5焊点的热循环应力应变进行了仿真研究,并与同条件下的SnPb钎料-Sn60Pb40结果进行了对比,结果显示无铅钎料大大地提高了焊点的热可靠性,热疲劳寿命是同样情况下SnPb钎料寿命的4倍以上。
所有这些研究为今后电子封装不同适用下的材料选择提供了借鉴,具有重要的实际指导意义。
With the development of electronic industry, electronic packaging grows up rapidly as an independent new high-tech calling. Among all the technology options, surface mounted technology (SMT) is the fastest expanding one which was thought as “A Revolution of the Electronic Packaging”. However, some of the disadvantages of SM connectors, such as inadequate availability and its less reliable solder joints, are also existing instead of many advantages of SM connectors. Generally, the low-cycle fatigue induced by thermal cycle is the major concern in the reliability of SMT .Due to the fine-small solder joint dimension, existing experiment measures can’t be used to monitor the stress and strain of solder inner, when thermal fatigue experiment is processing. So, the finite element model analysis is the most feasible means.
Different choice of material has a direct influence on final centralized stress, stress-strain distribution--change and life of solder joints. However international and domestic studies aren’t yet toward this direction at present. This text launches the subject to this blank to research in the reliability of the solder joint of BGA (Ball Grid Array ) under different material choice.
For the first time, the geometrical model for mechanical analysis of the solder joint is built directly from three-dimensional shape model of the BGA by ANSYS software. An unified viscoplastic constitutive law, the Anand model is applied to represent the inelastic deformation behavior for Sn60Pb40 solder. The mechanical performance is analyzed using finite element method .The distribution characteristics of stress and strain in solder joint are given at every time of thermal cycle. Besides, the variety rule of stress and strain with thermal cycle is acquired. Moreover, based on the strain data of the weakest site of the most dangerous solder ball in the array, fatigue life of thermally loaded BGA solder joints is predicted using the modificative coffin-Masson equation and reliability of the solder joints with different top-bottom material assembly is compared. Results indicate: The material heat matching of top-bottom base plate is more better, the life of assembly is more longer. The life-span of the solder joints assembled with ceramic encapsulation and FR4 base plate is 7 times than the one while adopting plastic encapsulation and FR4 base plate to make up; when sticking the Si chip to the FR4 base plate, the life-span is quite shortened; sticking the Si chip to the ceramic base plate can replace the former, because it not only raise the density of assembling, but also life-span of solder joints is prolonged to 6 times than the former; It is the compounding of ceramic to ceramic that match bestly.
Finally, by the same way, adopting the existing mechanical capability data of lead-free solder analyses its thermal reliability in contrast with the one of Sn60Pb40 solder under the ceramic-FR4 material compounding. Results show lead-free solder increases the reliability greatly. Its thermal fatigue life is 4 times than the one of SnPb solder.
The conclusion will provide a direction on material choice of electronic packaging in order to suit to different reliable requirement in future.
引文
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[2] 周德俭,吴兆华. 表面组装工艺技术[M]. 北京:国防工业出版社,2002.
[3] 《电子天府》表面安装技术编写组. 实用表面安装技术与元器件[M]. 北京:电子工艺出版社,1993:36-39.
[4] 王毅. 高密度高性能电子封装技术的现状和发展[M]. 北京:电子工艺出版社,1998,26(4):1-14.
[5] Lau J H. Handbook of Fine Pitch Surface Mount Technology[M]. New York: Van Nostrand Reinhold,1993.
[6] 田民波,林金堵,祝大同. 高密度封装基板[M]. 北京:清华大学出版社,2003.
[7] 杨邦朝,张经国. 多芯片组件(MCM)技术及其应用[M]. 成都:电子科技大学出版社,2001.
[8] 周德俭,吴兆华. 芯片尺寸封装(CSP)技术[J]. 电子工艺技术,1997,18(3):104-107.
[9] 胡志勇. 集成电路的发展和组装工艺的考虑[J]. 电子工艺技术,1998,19(6):234-236.
[10] Moore K, S Machugn, S Bosserman, J Stafford. Solder joint reliability of fine pitch solder bumped pad array carriers[J].Proceedings of NEPCON West,1990(12):264-274.
[11] 王国忠. 电子封装 SnPb 钎料焊点可靠性研究[D]. 上海:中国科学院上海冶金研究所,1999.
[12] Steinberg Dave S. Vibration Analysis for Electronic Equipment[M]. Second Edition, America:John wiley & Sons Inc.,1988.
[13] W W Lee, L T Nguyen, G S Selvaduray. Solder joint fatigue models: review and applicability to chip scale packages[J].Microelectronics Reliability, 2000,40:231-244.
[14] 黄大巍,方洪渊,钱乙余. 热循环载荷下 SMT 焊点应力应变过程的有限元分析[J]. 电子工艺技术,1997,18(1):6-14.
[15] 刘常康,周德俭. PBGA 焊点热疲劳寿命的正交试验及回归分析[J]. 电子工艺技术,1999,20(3):90-93.
[16] S M Heinrich, N J Nigro, A F Elkouh. Solder joint formation in surface mount technology, Part I: Analysis[J]. ASME Journal of Electronic Packaging, 1990,112(3):210-218.
[17] J Sauber. Prediction thermal fatigue lifetimes for SMT solder joints[J].ASME Journal of Electronic Packaging,1992,114(2):470-472.
[18] Robert Darveaux. Constitutive relations for tin-based solder joints[J]. IEEE-CHMT, 1992, 15(6):1013-1023.
[19] 周德俭,陈子辰, 潘开林, 吴兆华. PBGA 器件焊点成形建模与三维形态预测[J]. 浙江大学学报, 34(6):637-641.
[20] 耿照新,杨玉萍. CBGA 组件热变形的 2D-plane 42 模型有限元分析[J]. 首都师范大学学报(自然科学版),2003,24(2):29-32.
[21] 黄红艳,周德俭,吴兆华. 焊盘尺寸对SMT焊点可靠性的影响[J]. 桂林电子工业学院学报,2003,23(1):34-37.
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