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金属学报  2018, Vol. 54 Issue (7): 1077-1086    DOI: 10.11900/0412.1961.2017.00426
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倒装芯片无铅凸点β-Sn晶粒取向与电迁移交互作用
黄明亮(), 孙洪羽
大连理工大学材料科学与工程学院 先进连接技术辽宁省重点实验室 大连 116024
Interaction Between β-Sn Grain Orientation and Electromigration Behavior in Flip-Chip Lead-Free Solder Bumps
Mingliang HUANG(), Hongyu SUN
Key Laboratory of Liaoning Advanced Welding and Joining Technology, School of Materials Science and Engineering, Dalian University of Technology, Dalian 116024, China
引用本文:

黄明亮, 孙洪羽. 倒装芯片无铅凸点β-Sn晶粒取向与电迁移交互作用[J]. 金属学报, 2018, 54(7): 1077-1086.
Mingliang HUANG, Hongyu SUN. Interaction Between β-Sn Grain Orientation and Electromigration Behavior in Flip-Chip Lead-Free Solder Bumps[J]. Acta Metall Sin, 2018, 54(7): 1077-1086.

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摘要: 

采用原位电迁移实验研究了在150 ℃、1.0×104 A/cm2条件下倒装芯片Ni/Sn-3.0Ag-0.5Cu/Ni-P无铅凸点中β-Sn晶粒取向对金属间化合物(IMC)的聚集析出机制、阴极Ni芯片侧(UBM)溶解行为、电迁移失效机制以及电迁移驱动下β-Sn晶粒的旋转滑移机制的影响。原位观察发现,电迁移过程中(Ni, Cu)3Sn4类型IMC在凸点中仅沿着β-Sn晶粒的c轴方向析出,且倾向于在θ角(β-Sn晶粒的c轴与电子流动方向之间的夹角)较小的晶粒内析出;同时,阳极附近观察到β-Sn挤出现象,即凸点出现应力松弛。建立了阴极Ni UBM溶解量与β-Sn晶粒取向的关系模型:β-Sn晶粒取向决定阴极Ni UBM的溶解量,即当θ角很小时,Ni UBM会出现明显溶解;当θ角增大时,Ni UBM的溶解受到抑制,该模型与实验值基本吻合。电迁移导致β-Sn晶粒发生旋转滑移,认为是由于不同取向的相邻β-Sn晶粒中电迁移导致的空位通量不同,从而导致阳极晶界处于空位的过饱和,阴极晶界处于空位的未饱和状态,并促使空位沿着晶界出入于自由表面,最终在垂直方向上会产生空位梯度,由沿晶界的空位梯度对应的应力梯度产生的力矩使β-Sn晶粒发生旋转滑移。

关键词 电迁移β-Sn;各向异性阴极溶解IMC析出晶粒旋转    
Abstract

With the increasing demands for miniaturization, the electromigration (EM)-induced failure by diffusion anisotropy in β-Sn is expected to be more serious than that induced by local current crowding effect, especially with the downsizing of solder bumps. In this work, the effects of Sn grain orientation on intermetallic compound (IMC) precipitation, dissolution of Ni under bump metallurgy (UBM) at the cathode, EM failure mechanism as well as the EM-induced β-Sn grain rotation in Ni/Sn-3.0Ag-0.5Cu/Ni-P flip-chip interconnects undergoing solid-solid EM under a current density of 1.0×104 A/cm2 at 150 ℃ were in situ studied. (Ni, Cu)3Sn4-type IMCs precipitated in these β-Sn grains with a small angle θ (between the c-axis of Sn grain and electron flow direction), i.e., along the c-axis of β-Sn grains. Stress relaxation, squeezing β-Sn whiskers near the anode, was also observed during EM. A mathematical model on the relationship between the dissolution of Ni UBM and β-Sn grain orientation was proposed: when the c-axis of β-Sn grain is parallel to the electron flow direction, excessive dissolution of the cathode Ni UBM occurred due to the large diffusivity of Ni along the c-axis; when the c-axis of β-Sn grain is perpendicular to the electron flow direction, no evident dissolution of cathode Ni UBM occurred. The proposed model agreed well with the experimental results. EM-induced β-Sn grain rotation was attributed to the different vacancy fluxes caused by EM between adjacent grains of various grain orientation, when vacancies reached supersaturation and undersaturation at the interfaces of the anode and the cathode, respectively. Vacancy fluxes went through free surface along the interface, resulting in a normal vacancy concentration gradient. Accordingly, stress gradient produces a torque to rotate the β-Sn grain.

Key wordselectromigration    β-Sn;    anisotropy    cathode dissolution    IMC precipitation    grain rotation
收稿日期: 2017-10-13     
ZTFLH:  TN405  
基金资助:国家自然科学基金项目Nos.51475072、51511140289和51671046,中央高校基本科研业务费项目No.DUT17ZD202
作者简介:

作者简介 黄明亮,男,1970年生,教授,博士

图1  倒装芯片Ni/Sn-3.0Ag-0.5Cu/ENEPIG无铅凸点结构示意图
图2  倒装芯片Ni/Sn-3.0Ag-0.5Cu/Ni-P无铅凸点回流后初始微观形貌
图3  1号倒装芯片Ni/Sn-3.0Ag-0.5Cu/Ni-P无铅凸点在150 ℃、1.0×104 A/cm2条件下原位电迁移不同时间后的微观形貌及沿轴向的EBSD取向分布
图4  2号倒装芯片Ni/Sn-3.0Ag-0.5Cu/Ni-P无铅凸点在150 ℃、1.0×104 A/cm2条件下原位电迁移不同时间后的微观形貌及沿RD方向的EBSD取向分布
图5  3号倒装芯片Ni/Sn-3.0Ag-0.5Cu/Ni-P无铅凸点在150 ℃、1.0×104 A/cm2条件下原位电迁移不同时间后的微观形貌及沿RD方向的EBSD取向分布
图6  4号倒装芯片Ni/Sn-3.0Ag-0.5Cu/Ni-P无铅凸点在150 ℃、1.0×104 A/cm2条件下原位电迁移不同时间后的微观形貌及沿RD方向的EBSD取向分布
图7  5号倒装芯片Ni/Sn-3.0Ag-0.5Cu/Ni-P无铅凸点在150 ℃、1.0×104 A/cm2条件下原位电迁移不同时间后的微观形貌及沿RD方向的EBSD取向分布
  
Axis ρ γ E D (150 ℃) / (cm2s-1) DT (150 ℃)
μΩcm 10-6-1 GPa Ag Cu Ni m2s-1
a 13.25 15.45 22.9 5.60×10-11 1.99×10-7 3.85×10-9 8.70×10-13
c 20.27 30.50 68.9 3.13×10-9 8.57×10-6 1.17×10-4 4.71×10-13
表1  β-Sn的各向异性参数[8,9,10]
Parameter Valne Unit
Z*[23] 3.5 -
CNi 1.858×1024 atomsm-3
T 423 K
i 1.0×108 Am-2
ρSn 1.18×10-7 Ωm
Ω 6.6×10-6 m3mol-1
l 1.0 μm
δ 0.0125 μm
表2  计算用材料参数
图9  阴极Ni UBM消耗和q角的函数关系
图10  倒装芯片Sn-3.0Ag-0.5Cu无铅凸点中电迁移致晶粒旋转示意图
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