高密度封装中互连焊点的热迁移研究
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摘要
随着高密度电子封装向小型化和高集成度的方向迅速发展，由焦耳热效应所引发的元器件互连焊点中的热迁移现象，已逐渐成为影响互连结构可靠性的主要问题之一。本文主要研究高密度焊点中的热迁移现象，包括实验装置及样品结构设计和数值模拟，共晶SnPb钎料层及商用BGA元件倒装芯片SnPb复合焊点中的热迁移现象观察及分析，热迁移对焊点界面金属间化合物形成及生长的影响评估，并在扩散学基础上，对温度梯度作用下钎料各个元素原子的迁移模式的讨论及分析，以及对热迁移理论中的关键常数和不同条件下的热迁移驱动力等参数的推理及计算。
为了使热迁移的观察及研究能脱离电迁移实验而独立出来，项目组自行研发了一套由可控温加热棒及帕尔贴元件组成的加热—制冷装置。同时针对这套装置，设计了四种Cu片（块）/钎料层/Cu片（块）的样品结构，并利用Ansys模拟这四种样品中的温度及温度梯度分布。结果表明这些样品中钎料层内的温度梯度都高于SnPb钎料热迁移温度梯度阈值1000K/cm，即设计的装置及样品结构满足热迁移实验要求。
在热迁移项目研究前期，采用的是自行设计的Cu片/SnPb钎料层/Cu棒的样品结构，结合固体加热—液体冷却的实验装置，对共晶SnPb钎料在高温下的热迁移现象进行观察和研究。实验前的数值模拟结果表明，钎料层中的温度梯度大部分处于1430K/cm~1579K/cm范围内，最大值可达1875K/cm。在热迁移实验过程中，前期的钎料内部并未发生明显变化。但在温度梯度加载了20小时之后，Pb相开始向冷端迁移，并在冷端以不规则的块状形态聚集。随着温度梯度加载时间的延长，Pb相向钎料层冷端迁移并聚集的现象越来越明显。另一方面，基于原子扩散理论，证明了在SnPb合金中，在面心立方中以空位机制扩散的Sn原子和Pb原子，在温度梯度作用下的迁移模式均是由热端迁移至冷端。同时，两者的迁移速率取决于环境温度。因此证明了在热迁移过程中，哪种元素能成为温度梯度作用下的主要迁移元素，必须取决于以上两个条件。此外，在微观观察的基础上，计算出了热迁移理论中的关键常数，即Pb原子的传递热Q*值为27.2kJ/mol，而在此条件下的热迁移驱动力为1.48×10~(-17)N。
在热迁移项目研究后期，主要以商用BGA元件中倒装芯片SnPb复合焊点为研究对象，分析在室温及高温条件下热迁移效应对焊点可靠性的影响。在室温25°C的环境下，通入密度为3×10~4A/cm~2的电流后，倒装芯片Si片侧及基板侧的温度分别为93.2°C和72.9°C。未通电焊点中的温度梯度主要集中在347K/cm~800K/cm范围内，最大值可达2388K/cm。在热迁移实验过程中，前期的钎料内部并未发生明显变化。但在温度梯度加载了100小时之后，焊点下部共晶SnPb钎料中的Sn相开始向冷端迁移，并于400小时之后在冷端界面附近形成了一层致密的聚集层，平均厚度达7.9μm。此外，在微观结果基础上，计算出了Sn原子的Q*值为22.1kJ/mol。同时，也计算出此条件下未通电焊点中的热迁移驱动力为9.1×10~(-17)N,低于通电焊点中的电迁移驱动力1.3×10-15N。因此可以判定在低温的通电倒装芯片焊点中，电迁移在原子扩散中起主导作用，而非热迁移。另外，通过针对热迁移现象对焊点界面IMC形成及生长的研究发现，在冷端界面处，热迁移能加速Cu6Sn5的生长，而明显抑制Cu_3Sn的生长。主要原因为：一方面，热迁移后在冷端界面处形成的Sn相聚集层给Cu-Sn化合物的生长提供了充足的Sn原子；另一方面，IMC层内部900K/cm~1264K/cm的温度梯度可以促进Sn原子由Sn相聚集层向IMC内迁移，使Cu-Sn反应优先生成Cu6Sn5。
同时，针对商用BGA元件中倒装芯片SnPb复合焊点在高温条件下的热迁移效应也进行了研究。在100°C的环境下，通入密度为3×10~4A/cm~2的电流后，倒装芯片Si片侧及基板侧的温度分别为125.2°C和160.9°C。未通电焊点中的温度梯度主要集中在1062K/cm~2450K/cm范围内，最大值可达7309K/cm。基于微观观察结果，确定了Sn原子在焊点中的宏观迁移模式为：相粗化→冷端附近从中心至两侧横向迁移→从冷端向热端横向及纵向迁移→在高Pb及共晶SnPb钎料交界处聚集。数值模拟分析了高温下本实验样品中并未出现明显缺陷，是由于底部填充胶的存在降低了焊点内部的温度梯度，从而减缓了热迁移失效。另外，Sn原子偏向于在高Pb及共晶SnPb钎料交界处聚集，也是两种钎料中温度梯度分布不均所致。
With the miniaturization trend and functional demand in high-density microelectronicpackaging, the thermomigration (TM) in flip chip solder joints due to the serious joule heatingbecomes a major reliability issue in recent years. This thesis presents a study of TM apparatusand specimen design, as well as the TM investigation in the eutectic SnPb solder bulk andcomposite SnPb flip chip solder bumps at both high and low ambient temperatures.
In order to carry out the TM experiment separated from EM behavior in the solder layer,a novel apparatus, which consists of two temperature controlled heating rods and a Pelitercooler to serve as the heating source and heat sink respectively, has been developed. Fourtypes of sandwich specimen with Cu/Solder/Cu structure have also been designed to matchthe apparatus well. FE simulation shows that the thermal gradients across the solder layers inall these specimens can rise up to be higher than the TM threshold value1000K/cm.
The investigation of TM in eutectic SnPb solder layer at high ambient temperature hasbeen performed in a Cu plate/SnPb solder layer/Cu bar specimen. FE simulation shows thatthe thermal gradients in the target solder layer are mainly in the range of1430K/cm~1579K/cm, and the highest one can reach1875K/cm. The microstructure in the eutectic SnPbsolder layer does not vary too much at the early stage of TM. But Pb phases start to migrate tothe cold side and accumulate there with anomalous shape after TM20h, which will get moreseriously with the TM duration increases. Besides, based on the atomic diffusion theory, it hasbeen demonstrated that in SnPb alloy, both Sn and Pb atoms, which migrate in Pb and Snface-centered cubic with vacancy diffusion mode, have the positive net atomic flow from hotsite to cold site under thermal gradient loading. However, the diffusion rate of each elementwill depend on the ambient temperature. Thus, it has been clarified that during TM, whichelement can be regards as the primary diffusion atom is determined by the combined effect ofboth these two factors. Moreover, the key parameter Q*of Pb atoms is calculated to be27.2KJ/mol, and the TM driving force under the thermal gradient of1430K/cm at170°C is1.48×10~(-17)N.
The effect of TM on the composite SnPb flip chip solder bump at low ambienttemperature has been studied. During3×10~4A/cm~2current stressing at25°C, the final stabletemperatures on the Si die and the substrate can reach93.2°C and72.9°C respectively. Thethermal gradients in the unpowered bump are mainly in the range of347K/cm~800K/cm,and the peck value can reach2388K/cm. At the early stage of TM, the microstructure in thesolder bump does not vary too much. But Sn phases in the lower eutectic SnPb solder start tomigrate to the cold side after TM100h, and accumulate there eventually as a7.9μm thickcompact layer after TM400h. The key parameter Q*of Sn atoms is proposed to be22.1KJ/mol, and the TM driving force in the unpowered bump at low ambient temperature is9.1×10~(-17)N, which is much smaller than EM driving force in the powered bump of1.3×10-15N.Thus, it can be concluded that EM will definitely take lead the diffusion process at lowtemperature, rather than TM. Moreover, the digest of the IMC growth principle shows thatTM will accelerate the Cu6Sn5growth, but inhibit the Cu_3Sn development at the cold sideapparently. One reason is that after TM, the Sn atoms near the cold side can be sufficientlyprovided by the accumulated Sn rich layer; the other reason is that the thermal gradients in theIMC layer, which are in the range of900K/cm~1264K/cm, can also make a remarkableeffect on the Sn atoms to diffuse from the Sn-rich layer into the IMC, and then react with theCu atoms to generate Cu6Sn5preferentially.
The effect of TM on the SnPb composite flip chip solder bump at high ambienttemperature has also been studied. During3×10~4A/cm~2current stressing at100°C, the finalstable temperatures on the Si die and the substrate can reach125.2°C and160.9°C due to theJoule heating. The thermal gradients in the unpowered bump are mainly in the range of1062K/cm~2450K/cm, and the peck value can reach7309K/cm. Based on the microstructureobservation, the macroscopic TM diffusion path of Sn atoms in the solder bump can beidentified as: phase coarsen→horizontal movement from the center to the edge near thesubstrate side→horizontal and vertical migration from the cold side to the hot side→accumulation at the connecting area between high-Pb and eutectic SnPb solder bulk. Moreimportantly, the analysis has been stated to explain two divergences of unique Sn and Pb phases’ redistribution in our study. Firstly, for no obvious void or micro crack at the interfaceof the hot side after TM at high ambient temperature, FE simulation proves that the existingunderfill layer in our commercial product will reduce the thermal gradient across the solderbump effectively, which will bring in a much gentler atomic migration even when the wholecomponent is stressed by such high density current. Secondly, for the accumulation of Sn-richphases at the connecting area between high-Pb and eutectic SnPb solder bulk, it can beexplained that as the thermal gradients in the high-Pb and eutectic SnPb solder bulk arenon-uniform, the thermal energy change need Sn atoms to overcome in the high-Pb solder islarger than that in the eutectic SnPb solder. Thus, when the stress gradient driving force isconstant, the Sn atoms tend to diffuse in the eutectic SnPb solder much easier than in the highPb solder bulk, which will lead to the final accumulation at the connecting area after TM.
为了使热迁移的观察及研究能脱离电迁移实验而独立出来，项目组自行研发了一套由可控温加热棒及帕尔贴元件组成的加热—制冷装置。同时针对这套装置，设计了四种Cu片（块）/钎料层/Cu片（块）的样品结构，并利用Ansys模拟这四种样品中的温度及温度梯度分布。结果表明这些样品中钎料层内的温度梯度都高于SnPb钎料热迁移温度梯度阈值1000K/cm，即设计的装置及样品结构满足热迁移实验要求。
在热迁移项目研究前期，采用的是自行设计的Cu片/SnPb钎料层/Cu棒的样品结构，结合固体加热—液体冷却的实验装置，对共晶SnPb钎料在高温下的热迁移现象进行观察和研究。实验前的数值模拟结果表明，钎料层中的温度梯度大部分处于1430K/cm~1579K/cm范围内，最大值可达1875K/cm。在热迁移实验过程中，前期的钎料内部并未发生明显变化。但在温度梯度加载了20小时之后，Pb相开始向冷端迁移，并在冷端以不规则的块状形态聚集。随着温度梯度加载时间的延长，Pb相向钎料层冷端迁移并聚集的现象越来越明显。另一方面，基于原子扩散理论，证明了在SnPb合金中，在面心立方中以空位机制扩散的Sn原子和Pb原子，在温度梯度作用下的迁移模式均是由热端迁移至冷端。同时，两者的迁移速率取决于环境温度。因此证明了在热迁移过程中，哪种元素能成为温度梯度作用下的主要迁移元素，必须取决于以上两个条件。此外，在微观观察的基础上，计算出了热迁移理论中的关键常数，即Pb原子的传递热Q*值为27.2kJ/mol，而在此条件下的热迁移驱动力为1.48×10~(-17)N。
在热迁移项目研究后期，主要以商用BGA元件中倒装芯片SnPb复合焊点为研究对象，分析在室温及高温条件下热迁移效应对焊点可靠性的影响。在室温25°C的环境下，通入密度为3×10~4A/cm~2的电流后，倒装芯片Si片侧及基板侧的温度分别为93.2°C和72.9°C。未通电焊点中的温度梯度主要集中在347K/cm~800K/cm范围内，最大值可达2388K/cm。在热迁移实验过程中，前期的钎料内部并未发生明显变化。但在温度梯度加载了100小时之后，焊点下部共晶SnPb钎料中的Sn相开始向冷端迁移，并于400小时之后在冷端界面附近形成了一层致密的聚集层，平均厚度达7.9μm。此外，在微观结果基础上，计算出了Sn原子的Q*值为22.1kJ/mol。同时，也计算出此条件下未通电焊点中的热迁移驱动力为9.1×10~(-17)N,低于通电焊点中的电迁移驱动力1.3×10-15N。因此可以判定在低温的通电倒装芯片焊点中，电迁移在原子扩散中起主导作用，而非热迁移。另外，通过针对热迁移现象对焊点界面IMC形成及生长的研究发现，在冷端界面处，热迁移能加速Cu6Sn5的生长，而明显抑制Cu_3Sn的生长。主要原因为：一方面，热迁移后在冷端界面处形成的Sn相聚集层给Cu-Sn化合物的生长提供了充足的Sn原子；另一方面，IMC层内部900K/cm~1264K/cm的温度梯度可以促进Sn原子由Sn相聚集层向IMC内迁移，使Cu-Sn反应优先生成Cu6Sn5。
同时，针对商用BGA元件中倒装芯片SnPb复合焊点在高温条件下的热迁移效应也进行了研究。在100°C的环境下，通入密度为3×10~4A/cm~2的电流后，倒装芯片Si片侧及基板侧的温度分别为125.2°C和160.9°C。未通电焊点中的温度梯度主要集中在1062K/cm~2450K/cm范围内，最大值可达7309K/cm。基于微观观察结果，确定了Sn原子在焊点中的宏观迁移模式为：相粗化→冷端附近从中心至两侧横向迁移→从冷端向热端横向及纵向迁移→在高Pb及共晶SnPb钎料交界处聚集。数值模拟分析了高温下本实验样品中并未出现明显缺陷，是由于底部填充胶的存在降低了焊点内部的温度梯度，从而减缓了热迁移失效。另外，Sn原子偏向于在高Pb及共晶SnPb钎料交界处聚集，也是两种钎料中温度梯度分布不均所致。
With the miniaturization trend and functional demand in high-density microelectronicpackaging, the thermomigration (TM) in flip chip solder joints due to the serious joule heatingbecomes a major reliability issue in recent years. This thesis presents a study of TM apparatusand specimen design, as well as the TM investigation in the eutectic SnPb solder bulk andcomposite SnPb flip chip solder bumps at both high and low ambient temperatures.
In order to carry out the TM experiment separated from EM behavior in the solder layer,a novel apparatus, which consists of two temperature controlled heating rods and a Pelitercooler to serve as the heating source and heat sink respectively, has been developed. Fourtypes of sandwich specimen with Cu/Solder/Cu structure have also been designed to matchthe apparatus well. FE simulation shows that the thermal gradients across the solder layers inall these specimens can rise up to be higher than the TM threshold value1000K/cm.
The investigation of TM in eutectic SnPb solder layer at high ambient temperature hasbeen performed in a Cu plate/SnPb solder layer/Cu bar specimen. FE simulation shows thatthe thermal gradients in the target solder layer are mainly in the range of1430K/cm~1579K/cm, and the highest one can reach1875K/cm. The microstructure in the eutectic SnPbsolder layer does not vary too much at the early stage of TM. But Pb phases start to migrate tothe cold side and accumulate there with anomalous shape after TM20h, which will get moreseriously with the TM duration increases. Besides, based on the atomic diffusion theory, it hasbeen demonstrated that in SnPb alloy, both Sn and Pb atoms, which migrate in Pb and Snface-centered cubic with vacancy diffusion mode, have the positive net atomic flow from hotsite to cold site under thermal gradient loading. However, the diffusion rate of each elementwill depend on the ambient temperature. Thus, it has been clarified that during TM, whichelement can be regards as the primary diffusion atom is determined by the combined effect ofboth these two factors. Moreover, the key parameter Q*of Pb atoms is calculated to be27.2KJ/mol, and the TM driving force under the thermal gradient of1430K/cm at170°C is1.48×10~(-17)N.
The effect of TM on the composite SnPb flip chip solder bump at low ambienttemperature has been studied. During3×10~4A/cm~2current stressing at25°C, the final stabletemperatures on the Si die and the substrate can reach93.2°C and72.9°C respectively. Thethermal gradients in the unpowered bump are mainly in the range of347K/cm~800K/cm,and the peck value can reach2388K/cm. At the early stage of TM, the microstructure in thesolder bump does not vary too much. But Sn phases in the lower eutectic SnPb solder start tomigrate to the cold side after TM100h, and accumulate there eventually as a7.9μm thickcompact layer after TM400h. The key parameter Q*of Sn atoms is proposed to be22.1KJ/mol, and the TM driving force in the unpowered bump at low ambient temperature is9.1×10~(-17)N, which is much smaller than EM driving force in the powered bump of1.3×10-15N.Thus, it can be concluded that EM will definitely take lead the diffusion process at lowtemperature, rather than TM. Moreover, the digest of the IMC growth principle shows thatTM will accelerate the Cu6Sn5growth, but inhibit the Cu_3Sn development at the cold sideapparently. One reason is that after TM, the Sn atoms near the cold side can be sufficientlyprovided by the accumulated Sn rich layer; the other reason is that the thermal gradients in theIMC layer, which are in the range of900K/cm~1264K/cm, can also make a remarkableeffect on the Sn atoms to diffuse from the Sn-rich layer into the IMC, and then react with theCu atoms to generate Cu6Sn5preferentially.
The effect of TM on the SnPb composite flip chip solder bump at high ambienttemperature has also been studied. During3×10~4A/cm~2current stressing at100°C, the finalstable temperatures on the Si die and the substrate can reach125.2°C and160.9°C due to theJoule heating. The thermal gradients in the unpowered bump are mainly in the range of1062K/cm~2450K/cm, and the peck value can reach7309K/cm. Based on the microstructureobservation, the macroscopic TM diffusion path of Sn atoms in the solder bump can beidentified as: phase coarsen→horizontal movement from the center to the edge near thesubstrate side→horizontal and vertical migration from the cold side to the hot side→accumulation at the connecting area between high-Pb and eutectic SnPb solder bulk. Moreimportantly, the analysis has been stated to explain two divergences of unique Sn and Pb phases’ redistribution in our study. Firstly, for no obvious void or micro crack at the interfaceof the hot side after TM at high ambient temperature, FE simulation proves that the existingunderfill layer in our commercial product will reduce the thermal gradient across the solderbump effectively, which will bring in a much gentler atomic migration even when the wholecomponent is stressed by such high density current. Secondly, for the accumulation of Sn-richphases at the connecting area between high-Pb and eutectic SnPb solder bulk, it can beexplained that as the thermal gradients in the high-Pb and eutectic SnPb solder bulk arenon-uniform, the thermal energy change need Sn atoms to overcome in the high-Pb solder islarger than that in the eutectic SnPb solder. Thus, when the stress gradient driving force isconstant, the Sn atoms tend to diffuse in the eutectic SnPb solder much easier than in the highPb solder bulk, which will lead to the final accumulation at the connecting area after TM.
引文
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[19]C. Q. Ru. Thermomigration as a driving force for instability of electromigration inducedmass transport in interconnect lines. Journal of Materials Science,2000,35:5575~5579.
[20]Hsiang-Yao Hsiao and Chih Chen. Thermomigration in Pb-free SnAg solder joint underalternating current stressing. Appl. Phys. Lett.,2009,94:092107.
[21]Basaran Cemal, Li Shidong, and Abdulhamid Mohd F. Thermomigration induceddegradation in solder alloys. J. Appl. Phys.,2009,103:123520.
[22]Chih Chen, H.M. Tong and K.N. Tu. Electromigration and Thermomigration in Pb-FreeFlip-Chip Solder Joints. Annual Review of Materials Research,2010,40:531~555.
[23]Chen Hsiao-Yun, Chen Chih and Tu King-Ning. Failure induced by thermomigration ofinterstitial Cu in Pb-free flip chip solder joints. Appl. Phys. Lett.,2008,93:122103.
[24]Cher Ming Tan, Guan Zhang, and Zhenghao Gan. Dynamic Study of the PhysicalProcesses in the Intrinsic Line Electromigration of Deep-Submicron Copper andAluminum Interconnects. IEEE Trans. on Devic. and Mater. Reliab.,2004,4:450~456.
[25]H. V. Nguyena, C. Salm, B. Krabbenbrgb, KWeide-Zaage, J. Bisschopb, A. J. Mouthma,F. G. Kuper. Effect of thermal gradients on the electromigration lifetime in powerelectronics. IEEE42ndAnnual International Reliability Physics Symposium, Phoenix,2004.
[26]C. Q. Ru. Thermomigration as a driving force for instability of electromigration inducedmass transport in interconnect lines. Journal of Materials Science,2000,35:5575~5579.
[27]Hsiang-Yao Hsiao and Chih Chen. Thermomigration in flip-chip SnPb solder joints underalternating current stressing. Appl. Phys. Lett.,2007,90:152105.
[28]Hua Ye, C. Basaran, and D. C. Hopkins. Experimental damage mechanics of micro/powerelectronics solder joints under electric current stresses. International Journal of DamageMechanics,2006,15:41~67.
[29]Kwang-Lung Lin and Shi-Ming Kuo. The Electromigration and ThermomigrationBehaviors of Pb-free Flip Chip Sn-3Ag-0.5Cu Solder Bumps.2006ElectronicComponents and Technology Conference,2006,667~672.
[30]Hua Ye, Cemal Basaran and Douglas C. Hopkins. Mechanical degradation ofmicroelectronics solder joints under current stressing. International Journal of Solids andStructures,2003,40:7269~7284.
[31]Dan Yang and Y. C. Chan. The characteristics of electromigration and thermomigration inflip chip solder joints. THERMINIC,2007,43~47.
[32]W. Roush and J. Jaspal. Thermomigration in Lead-Indium Solder. Proceedings of theElectron. Compon.32nd Conference, San Diego,1982,342~353.
[33]G. J. van Gurp, P. J. de Waard, and F. J. du Chatenier. Thermomigration in Indium films.Appl. Phys. Lett.,1984,45:1054~1056.
[34]G. J. van Gurp, P. J. de Waard, and F. J. du Chatenier. Thermomigration in Indium andImdium alloy films. J. Appl. Phys.,1985,58:728~735.
[35]Fan-Yi Ouyang, Yi-Shao Lai, Andriy M. Gusak and K. N. Tu. Effect of entropyproduction on microstructure change in eutectic SnPb flip chip solder joints bythermomigration. Appl. Phys. Lett.,2006,89:221906.
[36]Aris Christou. Electromigration and electronic device degradation. John Wiley&Sons,Inc., Canada,1994,1~46.
[37]International Roadmap for Semiconductor Technology. Semiconductor IndustryAssociation,1999.
[38]C. Y. Liu, Chih Chen, and K. N. Tu. Electromigration in Sn-Pb solder strips as a functionof alloy composition. J. Appl. Phys.,2000,88:5703~5709.
[39]Dae-Gon Kim, Won-Chul Moon, Seung-Boo Jung. Effects of electromigration onmicrostructural evolution of eutectic SnPb flip chip solder bumps. MicroelectronicEngineering,2006,83:2391~2395.
[40]Hua Ye, Cemal Basaran, Douglas C. Hopkins. Pb phase coarsening in eutectic Pb/Sn flipchip solder joints under electric current stressing. International Journal of Solids andStructures,2004,41:2743~2755.
[41]Jae-Woong Nah, Jong Hoon Kim, Hyuck Mo Lee. Electromigration in flip chip solderbump of97Pb-3Sn/37Pb-63Sn combination structure. Acta Materialia,2004,52:129~136.
[42]J. W. Nah, J. O. Suh, and K. N. Tu. Effect of current crowding and Joule heating onelectromigration-induced failure in flip chip composite solder joints tested at roomtemperature. J. Appl. Phys.,2005,98:013715.
[43]Chih-ming Chen and Sinn-wen Chen. Electromigration effect upon the Sn-0.7wt%Cu/Niand Sn-3.5wt%Ag/Ni interfacial reactions. J. Appl. Phys.,2001,90:1208~1214.
[44]Mei-yau Du, Chih-ming Chen, Sinn-wen Chen. Effects upon interfacial reactions byelectric currents of reversing directions. Materials Chemistry and Physics,2003,82:818~825.
[45]Kumar, M. He, Z. Chen, P.S. Teo. Effect of electromigration on interfacial reactionsbetween electroless Ni-P and Sn-3.5%Ag solder. Thin Solid Films,2004,462:413~418.
[46]X. F. Zhang, J. D. Guo, and J. K. Shang. Abnormal polarity effect of electromigration onintermetallic compound formation in Sn-9Zn solder interconnect. Scripta Materialia,2007,57:513~516.
[47]K.N. Tu. Recent advances on electromigration in very-large-scale-integration ofinterconnect. J. Appl. Phys.,2003,94:5451~5473.
[48]K.N. Tu, A.M. Gusak, and M. Li. Physics and materials challenges for lead-free solders. J.Appl. Phys.,2003,93:1335~1353.
[49]Lingyun Zhang, Shengquan Ou, Joanne Huang. Effect of current crowding on voidpropagation at the interface between intermetallic compound and solder in flip chipsolder joints. Appl. Phys. Lett.,2006,88:012106.
[50]H. Gan, K.N. Tu. Polarity effect of electromigration on kinetics of intermetalliccompound formation in Pb-free solder V-groove samples. J. Appl. Phys.,2005,18:063514.
[51]Q. T. Huynh, C. Y. Liu, Chih Chen. Electromigration in eutectic SnPb solder lines. J.Appl. Phys.,2001,89:4332~4335.
[52]T.Y. Lee, K.N. Tu. Electromigration of eutectic SnPb solder interconnects for flip chiptechnology. J. Appl. Phys.,2001,89:3189~3194.
[53]T. Y. Lee, K. N. Tu and D. R. Frear. Electromigration of eutectic SnPb and SnAg3.8Cu0.7flip chip solder bumps and under-bump metallization. J. Appl. Phys.,2001,90:4502~4508.
[54]Hua Ye, Cemal Basaran, Douglas C. Hopkins. Damage mechanics of microelectronicssolder joints under high current densities. International Journal of Solids and Structures,2003,40:4021~4032.
[55]C.-M. Chen, S.-W. Chen. Electromigration effect upon the Sn/Ag and Sn/Ni interfacialreactions at various temperatures. Acta Materialia,2002,50:2461~2469.
[56]Brook Chao, Seung-Hyun Chae, Xuefeng Zhang. Investigation of diffusion andelectromigration parameters for Cu-Sn intermetallic compounds in Pb-free solders usingsimulated annealing. Acta Materialia,2007,55:2805~2814.
[57]Aris Christou. Electromigration and electronic device degradation. John Wiley&Sons,Inc., Canada,1994,1~46.
[58]International Roadmap for Semiconductor Technology. Semiconductor IndustryAssociation,1999.
[59]P.S. Ho, H.B. Huntington. Electromigration and void observation in silver. J. Phys. Chem.Solids,1966,27:1319~1329.
[60]J.F. D’amico, H.B. Huntington. Electromigration and thermomigration inGamma-uranium. J. Phys. Chem. Solids,1969,30:2607~2621.
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[63]D.A. Golopentia, H. B. Huntington. A study of electromigration of nickel in lead. J. Phys.Chem. Solids,1978,39:975~984.
[64]T.W. Duryea, H.B. Huntington. The driving force for electromigration of an atomadsorbed on simple metal surface. Surface Science,1988,199:261~281.
[65]T. L. Shao, Y. H. Chen, S. H. Chiu. Electromigration failure mechanisms for SnAg3.5solder bumps on Ti/Cr-Cu/Cu and Ni.P./Au metallization pads. J. Appl. Phys.,2004,96:4518~4524.
[66]Y H Lin, C M Tsai, Y C Hu. Electromigration-Induced Failure in Flip-Chip Solder Joints.Journal of Electronic Materials,2005,34:27~33.
[67]T Hasegawa, M Saka, Y Watanabe. Direct Measurement of Local Surface Temperature ofEutectic Solder for Determining Electromigration Pattern. Journal of Electronic Materials,2006,35:1074~1081.
[68]Yi-Shao Lai, Chin-Li Kao. Electrothermal coupling analysis of current crowding andJoule heating in flip-chip packages. Microelectronics Reliability,2006,46:1357-1368.
[69]J.S. Zhang, Y.C. Chan, Y.P. Wu. Electromigration of Pb-free solder under a low level ofcurrent density. Journal of Alloys and Compounds,2007,4:40~47.
[70]S. W. Liang, Y. W. Chang, T. L. Shao. Effect of three-dimensional current andtemperature distributions on void formation and propagation in flip-chip solder jointsduring electromigration. Appl. Phys. Lett.,2006,89:022117.
[71]C Y Hsu, D J Yao, S W Liang. Temperature and Current-Density Distributions inFlip-Chip Solder Joints with Cu Trace. Journal of Electronic Materials,2006,35:947~953.
[72]Fan-Yi Ouyang, K. N. Tu, Chin-Li Kao. Effect of electromigration in the anodic Alinterconnect on melting of flip chip solder joints. Appl. Phys. Lett.,2007,90:211914.
[73]Fan-Yi Ouyang, Annie T. Huang, and K. N. Tu. Thermomigration in SnPb compositesolder joints and wires.2006Electronic Components and Technology Conference,2006,1974~1978.
[74]Glenn A. Rinne. Issues in accelerated electromigration of solder bumps. MicroelectronicsReliability,2003,43:1975~1980.
[75]D. Gupta, K. Vieregge and W. Gust. Interface Diffusion In Eutectic Pb-Sn Solder.Diffusion In Eutectic Solder,5~12.
[76]张金松，纯锡覆层晶须生长及无铅焊点电迁移的研究，博士学位论文，华中科技大学图书馆，2008.
[77]K. N. Tu. Recent Advances on Electromigration in Very-Large-Scale-Integration ofInterconnects. Journal of Applied Physics,2003,94:5451~5473.
[78]李晓延，严永长，史耀武，金属间化合物对SnAgCu/Cu界面破坏行为的影响。机械强度，2005，27：666~671。
[79]李凤辉，李晓延，严永长，SnAgCu无铅钎料对接接头时效过程中IMC的生长。上海交通大学学报，2007，41：163~169。
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[19]C. Q. Ru. Thermomigration as a driving force for instability of electromigration inducedmass transport in interconnect lines. Journal of Materials Science,2000,35:5575~5579.
[20]Hsiang-Yao Hsiao and Chih Chen. Thermomigration in Pb-free SnAg solder joint underalternating current stressing. Appl. Phys. Lett.,2009,94:092107.
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[23]Chen Hsiao-Yun, Chen Chih and Tu King-Ning. Failure induced by thermomigration ofinterstitial Cu in Pb-free flip chip solder joints. Appl. Phys. Lett.,2008,93:122103.
[24]Cher Ming Tan, Guan Zhang, and Zhenghao Gan. Dynamic Study of the PhysicalProcesses in the Intrinsic Line Electromigration of Deep-Submicron Copper andAluminum Interconnects. IEEE Trans. on Devic. and Mater. Reliab.,2004,4:450~456.
[25]H. V. Nguyena, C. Salm, B. Krabbenbrgb, KWeide-Zaage, J. Bisschopb, A. J. Mouthma,F. G. Kuper. Effect of thermal gradients on the electromigration lifetime in powerelectronics. IEEE42ndAnnual International Reliability Physics Symposium, Phoenix,2004.
[26]C. Q. Ru. Thermomigration as a driving force for instability of electromigration inducedmass transport in interconnect lines. Journal of Materials Science,2000,35:5575~5579.
[27]Hsiang-Yao Hsiao and Chih Chen. Thermomigration in flip-chip SnPb solder joints underalternating current stressing. Appl. Phys. Lett.,2007,90:152105.
[28]Hua Ye, C. Basaran, and D. C. Hopkins. Experimental damage mechanics of micro/powerelectronics solder joints under electric current stresses. International Journal of DamageMechanics,2006,15:41~67.
[29]Kwang-Lung Lin and Shi-Ming Kuo. The Electromigration and ThermomigrationBehaviors of Pb-free Flip Chip Sn-3Ag-0.5Cu Solder Bumps.2006ElectronicComponents and Technology Conference,2006,667~672.
[30]Hua Ye, Cemal Basaran and Douglas C. Hopkins. Mechanical degradation ofmicroelectronics solder joints under current stressing. International Journal of Solids andStructures,2003,40:7269~7284.
[31]Dan Yang and Y. C. Chan. The characteristics of electromigration and thermomigration inflip chip solder joints. THERMINIC,2007,43~47.
[32]W. Roush and J. Jaspal. Thermomigration in Lead-Indium Solder. Proceedings of theElectron. Compon.32nd Conference, San Diego,1982,342~353.
[33]G. J. van Gurp, P. J. de Waard, and F. J. du Chatenier. Thermomigration in Indium films.Appl. Phys. Lett.,1984,45:1054~1056.
[34]G. J. van Gurp, P. J. de Waard, and F. J. du Chatenier. Thermomigration in Indium andImdium alloy films. J. Appl. Phys.,1985,58:728~735.
[35]Fan-Yi Ouyang, Yi-Shao Lai, Andriy M. Gusak and K. N. Tu. Effect of entropyproduction on microstructure change in eutectic SnPb flip chip solder joints bythermomigration. Appl. Phys. Lett.,2006,89:221906.
[36]Aris Christou. Electromigration and electronic device degradation. John Wiley&Sons,Inc., Canada,1994,1~46.
[37]International Roadmap for Semiconductor Technology. Semiconductor IndustryAssociation,1999.
[38]C. Y. Liu, Chih Chen, and K. N. Tu. Electromigration in Sn-Pb solder strips as a functionof alloy composition. J. Appl. Phys.,2000,88:5703~5709.
[39]Dae-Gon Kim, Won-Chul Moon, Seung-Boo Jung. Effects of electromigration onmicrostructural evolution of eutectic SnPb flip chip solder bumps. MicroelectronicEngineering,2006,83:2391~2395.
[40]Hua Ye, Cemal Basaran, Douglas C. Hopkins. Pb phase coarsening in eutectic Pb/Sn flipchip solder joints under electric current stressing. International Journal of Solids andStructures,2004,41:2743~2755.
[41]Jae-Woong Nah, Jong Hoon Kim, Hyuck Mo Lee. Electromigration in flip chip solderbump of97Pb-3Sn/37Pb-63Sn combination structure. Acta Materialia,2004,52:129~136.
[42]J. W. Nah, J. O. Suh, and K. N. Tu. Effect of current crowding and Joule heating onelectromigration-induced failure in flip chip composite solder joints tested at roomtemperature. J. Appl. Phys.,2005,98:013715.
[43]Chih-ming Chen and Sinn-wen Chen. Electromigration effect upon the Sn-0.7wt%Cu/Niand Sn-3.5wt%Ag/Ni interfacial reactions. J. Appl. Phys.,2001,90:1208~1214.
[44]Mei-yau Du, Chih-ming Chen, Sinn-wen Chen. Effects upon interfacial reactions byelectric currents of reversing directions. Materials Chemistry and Physics,2003,82:818~825.
[45]Kumar, M. He, Z. Chen, P.S. Teo. Effect of electromigration on interfacial reactionsbetween electroless Ni-P and Sn-3.5%Ag solder. Thin Solid Films,2004,462:413~418.
[46]X. F. Zhang, J. D. Guo, and J. K. Shang. Abnormal polarity effect of electromigration onintermetallic compound formation in Sn-9Zn solder interconnect. Scripta Materialia,2007,57:513~516.
[47]K.N. Tu. Recent advances on electromigration in very-large-scale-integration ofinterconnect. J. Appl. Phys.,2003,94:5451~5473.
[48]K.N. Tu, A.M. Gusak, and M. Li. Physics and materials challenges for lead-free solders. J.Appl. Phys.,2003,93:1335~1353.
[49]Lingyun Zhang, Shengquan Ou, Joanne Huang. Effect of current crowding on voidpropagation at the interface between intermetallic compound and solder in flip chipsolder joints. Appl. Phys. Lett.,2006,88:012106.
[50]H. Gan, K.N. Tu. Polarity effect of electromigration on kinetics of intermetalliccompound formation in Pb-free solder V-groove samples. J. Appl. Phys.,2005,18:063514.
[51]Q. T. Huynh, C. Y. Liu, Chih Chen. Electromigration in eutectic SnPb solder lines. J.Appl. Phys.,2001,89:4332~4335.
[52]T.Y. Lee, K.N. Tu. Electromigration of eutectic SnPb solder interconnects for flip chiptechnology. J. Appl. Phys.,2001,89:3189~3194.
[53]T. Y. Lee, K. N. Tu and D. R. Frear. Electromigration of eutectic SnPb and SnAg3.8Cu0.7flip chip solder bumps and under-bump metallization. J. Appl. Phys.,2001,90:4502~4508.
[54]Hua Ye, Cemal Basaran, Douglas C. Hopkins. Damage mechanics of microelectronicssolder joints under high current densities. International Journal of Solids and Structures,2003,40:4021~4032.
[55]C.-M. Chen, S.-W. Chen. Electromigration effect upon the Sn/Ag and Sn/Ni interfacialreactions at various temperatures. Acta Materialia,2002,50:2461~2469.
[56]Brook Chao, Seung-Hyun Chae, Xuefeng Zhang. Investigation of diffusion andelectromigration parameters for Cu-Sn intermetallic compounds in Pb-free solders usingsimulated annealing. Acta Materialia,2007,55:2805~2814.
[57]Aris Christou. Electromigration and electronic device degradation. John Wiley&Sons,Inc., Canada,1994,1~46.
[58]International Roadmap for Semiconductor Technology. Semiconductor IndustryAssociation,1999.
[59]P.S. Ho, H.B. Huntington. Electromigration and void observation in silver. J. Phys. Chem.Solids,1966,27:1319~1329.
[60]J.F. D’amico, H.B. Huntington. Electromigration and thermomigration inGamma-uranium. J. Phys. Chem. Solids,1969,30:2607~2621.
[61]H.B. Hungtington. Electro-and thermomigration in metals. Seminar of the AmericanSociety of Metals,1972,12:155~184.
[62]H.B. Hungtington. Effect of driving forces on atom motion. Thin Solid Films,1975,25:265~280.
[63]D.A. Golopentia, H. B. Huntington. A study of electromigration of nickel in lead. J. Phys.Chem. Solids,1978,39:975~984.
[64]T.W. Duryea, H.B. Huntington. The driving force for electromigration of an atomadsorbed on simple metal surface. Surface Science,1988,199:261~281.
[65]T. L. Shao, Y. H. Chen, S. H. Chiu. Electromigration failure mechanisms for SnAg3.5solder bumps on Ti/Cr-Cu/Cu and Ni.P./Au metallization pads. J. Appl. Phys.,2004,96:4518~4524.
[66]Y H Lin, C M Tsai, Y C Hu. Electromigration-Induced Failure in Flip-Chip Solder Joints.Journal of Electronic Materials,2005,34:27~33.
[67]T Hasegawa, M Saka, Y Watanabe. Direct Measurement of Local Surface Temperature ofEutectic Solder for Determining Electromigration Pattern. Journal of Electronic Materials,2006,35:1074~1081.
[68]Yi-Shao Lai, Chin-Li Kao. Electrothermal coupling analysis of current crowding andJoule heating in flip-chip packages. Microelectronics Reliability,2006,46:1357-1368.
[69]J.S. Zhang, Y.C. Chan, Y.P. Wu. Electromigration of Pb-free solder under a low level ofcurrent density. Journal of Alloys and Compounds,2007,4:40~47.
[70]S. W. Liang, Y. W. Chang, T. L. Shao. Effect of three-dimensional current andtemperature distributions on void formation and propagation in flip-chip solder jointsduring electromigration. Appl. Phys. Lett.,2006,89:022117.
[71]C Y Hsu, D J Yao, S W Liang. Temperature and Current-Density Distributions inFlip-Chip Solder Joints with Cu Trace. Journal of Electronic Materials,2006,35:947~953.
[72]Fan-Yi Ouyang, K. N. Tu, Chin-Li Kao. Effect of electromigration in the anodic Alinterconnect on melting of flip chip solder joints. Appl. Phys. Lett.,2007,90:211914.
[73]Fan-Yi Ouyang, Annie T. Huang, and K. N. Tu. Thermomigration in SnPb compositesolder joints and wires.2006Electronic Components and Technology Conference,2006,1974~1978.
[74]Glenn A. Rinne. Issues in accelerated electromigration of solder bumps. MicroelectronicsReliability,2003,43:1975~1980.
[75]D. Gupta, K. Vieregge and W. Gust. Interface Diffusion In Eutectic Pb-Sn Solder.Diffusion In Eutectic Solder,5~12.
[76]张金松，纯锡覆层晶须生长及无铅焊点电迁移的研究，博士学位论文，华中科技大学图书馆，2008.
[77]K. N. Tu. Recent Advances on Electromigration in Very-Large-Scale-Integration ofInterconnects. Journal of Applied Physics,2003,94:5451~5473.
[78]李晓延，严永长，史耀武，金属间化合物对SnAgCu/Cu界面破坏行为的影响。机械强度，2005，27：666~671。
[79]李凤辉，李晓延，严永长，SnAgCu无铅钎料对接接头时效过程中IMC的生长。上海交通大学学报，2007，41：163~169。