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1.
Flip-chip solder joints with Cu/Ni/Al underbump metallurgy (UBM) on the chip and an Au/Ni surface finish on the substrate
were studied under current stressing at an ambient temperature of 150°C. Three different Ni thicknesses in the Cu/Ni/Al UBM
(0.3, 0.5, and 0.8 μm) were used in order to investigate the effect of the Ni thickness on reliability. The solder used was eutectic Pb-Sn, and
the applied current density was 5 × 103 A/cm2. The results show that the combined effect of current crowding and the local Joule heating near the entry points of electrons
into the joints induced asymmetric Ni UBM consumption. Once the Ni was exhausted in a certain region, this region became nonconductive
and the flow of electrons was diverted to the neighboring region. This neighboring region then became the place where electrons
entered the joint, and the Ni UBM there was consumed at an accelerated rate. This process repeated itself, and the Ni-depleted
region continued to extend, creating an ever larger nonconductive region. The solder joints eventually failed when the nonconductive
region extended across the entire contact window of the joints. This failure model supports the observation that joints with
a thicker Ni tend to have a longer average lifetime. 相似文献
2.
In flip-chip solder joints, thick Cu and Ni films have been used as under bump metallization (UBM) for Pb-free solders. In
addition, electromigration has become a crucial reliability concern for fine-pitch flip-chip solder joints. In this paper,
the three-dimensional (3-D) finite element method was employed to simulate the current-density and temperature distributions
for the eutectic SnPb solder joints with 5-μm Cu, 10-μm Cu, 25-μm Cu, and 25-μm Ni UBMs. It was found that the thicker the UBM is the lower the maximum current density inside the solder. The maximum current
density is 4.37 × 104 A/cm2, 1.69 × 104 A/cm2, 7.54 × 103 A/cm2, and 1.34 × 104 A/cm2, respectively, when the solder joints with the above four UBMs are stressed by 0.567 A. The solder joints with thick UBMs
can effectively relieve the current crowding effect inside the solder. In addition, the joint with the thicker Cu UBM has
a lower Joule heating effect in the solder. The joint with the 25-μm Ni UBM has the highest Joule heating effect among the four models. 相似文献
3.
Sang-Su Ha Jong-Woong Kim Jeong-Won Yoon Sang-Ok Ha Seung-Boo Jung 《Journal of Electronic Materials》2009,38(1):70-77
The electromigration of conventional Sn-37Pb and Pb-free Sn-3.0Ag-0.5Cu (in wt.%) solder bumps was investigated with a high
current density of 2.5 × 104 A/cm2 at 423 K using flip-chip specimens comprised of an upper Si chip and a lower bismaleimide triazine (BT) substrate. Electromigration
failure of the Sn-37Pb and Sn-3.0Ag-0.5Cu solder bumps occurred with complete consumption of electroless Ni immersion Au (ENIG)
underbump metallization (UBM) and void formation at the cathode side of the solder bump. Finite element analysis and computational
simulations indicated high current crowding of electrons in the patterned Cu on the Si chip side, whereas the solder bumps
and Cu line of the BT substrate had a relatively low density of flowing electrons. These findings were confirmed by the experimental
results. The electromigration reliability of the Sn-3.0Ag-0.5Cu solder joint was superior to that of Sn-37Pb. 相似文献
4.
高密度陶瓷封装倒装焊器件的焊点尺寸已降低至100μm以下,焊点电流密度达到10~4 A/cm~2以上,由此引发的电迁移失效成为不可忽视的问题。以陶瓷封装菊花链倒装焊器件为研究对象,开展了Sn10Pb90、Sn63Pb37焊点热电环境可靠性评估试验,通过电连接检测及扫描电子显微镜(SEM)等方法对焊点互连情况进行分析。结果表明,Sn63Pb37焊点阴极侧金属间化合物(IMC)增长明显,表现出明显的极化现象,IMC厚度的平方与通电时间呈线性关系。通电时间达到576 h后Sn63Pb37焊点阴极侧产生微裂纹,而Sn10Pb90焊点在通电576 h后仍未出现异常,表现出优异的电迁移可靠性。研究结果对于直径100μm微焊点的陶瓷封装倒装焊器件的应用具有重要的意义。 相似文献
5.
In this study, the different electromigration (EM) behaviors of eutectic Sn-Bi solder in the solid and molten states were
clarified using line-type Cu/Sn-Bi/Cu solder joints. When the eutectic Sn-Bi solder was in the solid state during the EM test,
a Bi-rich layer formed at the anode side while a Sn-rich band formed at the cathode side, and the intermetallic compound (IMC)
at the cathode side was thicker than that at the anode side. The growth of the Bi-rich layer exhibited a linear dependence
on the time of stressing. While the actual temperature of the solder joint increased to 140°C and the solder was in a molten
state or partially molten state, two separate Bi-rich layers formed at the anode side and a great many Cu6Sn5 IMC precipitates formed between the two Bi-rich layers. Also, the IMC layer at the cathode side was thinner than that at
the anode side. With a current-crowding-reduced structure, the products of diffusivity and effective charge number of Bi in
the eutectic Cu/Sn-Bi/Cu solder joints stressed with current density of 5 × 103 A/cm2 at 35°C, 55°C, and 75°C were calculated. 相似文献
6.
本文给出了倒装焊(flip-chip)焊点形态的能量控制方程,采用Surface Evolver软件模拟了倒装焊复合SnPb焊点(高Pb焊料凸点,共晶SnPb焊料焊点)的三维形态.利用焊点形态模拟的数据,分析了芯片和基板之间SnPb焊点的高度与焊点设计和焊接工艺参数的关系.研究表明:共晶SnPb焊料量存在临界值,当共晶SnPb焊料量小于临界值时,焊点的高度等于芯片上高Pb焊料凸点的半径值;当共晶SnPb焊料量大于临界值时,焊点的高度随共晶SnPb焊料量的增加而增加.另外,采用无量纲的形式给出了焊点高度与共晶焊料量、焊盘尺寸、芯片凸点的尺寸,芯片重量之间的关系模型,研究结果对倒装焊焊点形态的控制、工艺参数的优化和提高焊点可靠性具有指导意义. 相似文献
7.
影响封装可靠性的因素很多,其中对封装及供货厂商相关的封装设计方面的各种变量应该给予足够的重视。焊盘尺寸是影响焊点可靠性的关键因素之一,不同供货厂商的各种工艺造成焊盘尺寸方面的差异,对可靠性造成了极大的影响。有限元应力分析、波纹干涉测量试验及可靠性试验表明,基板厚度影响封装可靠性。文章采用有限元模拟来定量分析焊盘尺寸对PBGA封装可靠性的影响,把空气对空气热循环试验结果与FEM预测进行比较,讨论最佳焊盘尺寸,并预测对焊点可靠性的影响。 相似文献
8.
In flip-chip interconnects under current stressing, the primary current crowding effect occurs at the entrance edge of the
contact interface with the highest current density. In this study, an increased current density also occurred at the other
edge of the contact interface, followed by a selective dissolution of under bump metallization. After primary current crowding,
the rest of electrons flow to the metallization edge, followed by an abrupt change in direction toward the anode. Primary
current crowding is attributed to the electrical field change whereas the secondary crowding effect is due to the physical
blocking of the electron flow. Because this effect is not as great as that of primary current crowding, it must be assisted
by thermal diffusion. 相似文献
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电迁移可以引发芯片内部互连金属引线(单一元素)中的原子或离子沿电子运动方向移动.但是,在共晶锡铋焊点中,组成的元素为锡和铋而非单一元素.由于铋原子和锡原子在高电流密度下具有不同的迁移速率,因此共晶锡铋钎料具有独特的电迁移特性.实验中采用的电流密度为104A/cm2,同时焦耳热会引发焊点温度从25升高至49℃,富铋相在此温度下会发生明显粗化,除此之外,铋原子会首先到达正极界面处并形成坚硬的阻挡层,使得锡原子的定向运动受到阻碍,最终,富锡相会,凸起,其与负极界面问会有凹谷形成. 相似文献
12.
电迁移可以引发芯片内部互连金属引线(单一元素)中的原子或离子沿电子运动方向移动. 但是,在共晶锡铋焊点中,组成的元素为锡和铋而非单一元素. 由于铋原子和锡原子在高电流密度下具有不同的迁移速率,因此共晶锡铋钎料具有独特的电迁移特性. 实验中采用的电流密度为1E4A/cm2,同时焦耳热会引发焊点温度从25升高至49℃,富铋相在此温度下会发生明显粗化,除此之外,铋原子会首先到达正极界面处并形成坚硬的阻挡层,使得锡原子的定向运动受到阻碍,最终,富锡相会凸起,其与负极界面间会有凹谷形成. 相似文献
13.
Thermomechanical stress and strain in the solder joints of a dummy area array package were studied as electromigration occurred.
A current density of 0.4 × 104 A/cm2 was applied to this package, constructed with 9 × 9 solder joints in a daisy chain, to perform the electromigration test.
After 37 h, the first joint on the path of the electron flow broke off at the cathode, and the first three solder joints all
exhibited a typical accumulation of intermetallic compounds at the anode. Different solder joints exhibited dissimilar electromigration
states, such as steady state and nonsteady state. Finite element analysis indicated that during steady-state electromigration,
although the symmetrical structure produced uniform distributions of current density and Joule heating in all solder joints,
the distribution of temperature was nonuniform. This was due to the imbalanced heat dissipation, which in turn affected the
distribution of thermomechanical stress and strain in the solder joints. The maximum thermomechanical stress and strain, as
well the highest temperature and current crowding, appeared in the Ni/Cu layer of each joint. The strain in the Ni/Cu layer
was significant along the z-axis, but was constrained in the x–y plane. The thermomechanical stress and strain increased with advancing electromigration; thus, a potential delamination between
the Ni/Cu layer and the printed circuit board could occur. 相似文献
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采用Cu-Ni/Solder/Ni-Cu互连结构,在加载的电流密度为0.4×104 A/cm2的条件下,得到了界面阴极处金属原子的电迁移.数值模拟揭示了其原因是由于凸点互连结构的特殊性,电子流在流经凸点时会发生流向改变进而形成电流聚集,此处的电流密度超过电迁移的门槛值,从而诱发电迁移.运用高对流系数的热传导方法降低了互连焊点的实际温度,在电迁移的扩展阶段显著减小了高温引起的原子热迁移对电迁移的干扰;因此电迁移力是原子迁移的主要驱动力.在电迁移的快速失效阶段,原子的迁移是热迁移和电迁移共同作用的结果:电迁移力驱动阴极处原子的迁移,造成局部区域的快速温升,从而加剧此处原子的热迁移. 相似文献
18.
采用Cu-Ni/Solder/Ni-Cu互连结构,在加载的电流密度为0.4×104 A/cm2的条件下,得到了界面阴极处金属原子的电迁移.数值模拟揭示了其原因是由于凸点互连结构的特殊性,电子流在流经凸点时会发生流向改变进而形成电流聚集,此处的电流密度超过电迁移的门槛值,从而诱发电迁移.运用高对流系数的热传导方法降低了互连焊点的实际温度,在电迁移的扩展阶段显著减小了高温引起的原子热迁移对电迁移的干扰;因此电迁移力是原子迁移的主要驱动力.在电迁移的快速失效阶段,原子的迁移是热迁移和电迁移共同作用的结果:电迁移力驱动阴极处原子的迁移,造成局部区域的快速温升,从而加剧此处原子的热迁移. 相似文献
19.
在芯片紧密度、功耗都在增加的微电子封装领域,FBGA封装在同体积下有较大的存储容量。基于有限元和正交法,进行了FBGA焊点热循环载荷下的可靠性分析,并进行了更稳健的焊点结构参数优化设计。结果表明,焊点阵列对FBGA结构热可靠性有重要影响;优化方案组合为12×12焊点阵列,焊点径向尺寸为0.42 mm,焊点高度为0.38 mm,焊点间距为0.6 mm。经过优化验证,该优化方案的等效塑性应变范围较原始设计方案降低了89.92%,信噪比提高到17.72 dB,实现了焊点参数优化目标。 相似文献