Three-dimensional model for electromigration induced evolution of flip chip solder joints

Recent experiments have shown failure in flip chip micro solder joints induced by electromigration. This paper proposes a computational model to simulate the evolution of micro and sub-micro scale solder joints due to electromigration induced diffusion. Complicated morphological changes of the solder bump and multiple mechanisms cause a computational challenge. This is addressed by employing a diffuse interface model with multiple concentrations. To efficiently resolve complications, a semi-implicit Fourier spectral scheme and a biconjugate-gradient method are adopted. Results have demonstrated rich dynamics and solder breakage at the interface on the cathode side. This paper was recommended for publication in revised form by Associate Editor Dae-Eun Kim Dongchoul Kim received a B.S. degree in Mechanical Engineering from Yonsei University in 2000. He then went on to receive his M.S. and Ph.D. degrees from The University of Michigan in 2003 and 2005, respectively. Dr. Kim is currently an Assistant Professor at the School of Mechanical Engineering at Sogang University in Seoul, Korea. Dr. Kim’s research interests are in the area of computational analysis of micro/nanostructures.     

Characteristics of Sn-2.5Ag flip chip solder joints under thermal shock test conditions

The interfacial reaction between Cu pad coated with Au/Ni and solder bump of flip chip package, using Sn97.5wt.%-Ag2.5wt%, was studied under thermal shock stress. All joints were subjected to thermal shock test with −65°C/+150°C temperature range. For the Sn-2.5Ag solder, a scallop-like (Cu,Ni)₆Sn₅ intermetallic compound was formed in the solder matrix after 20 cycles of thermal shock. (Cu,Ni)₆Sn₅ was detached from the interface as (Ni,Cu)₃Sn₄ grew underneath the (Cu,Ni)₆Sn₅ IMC(Intermetallic Compound), whereas the elements of Sn, Ni and Cu were moved by interdiffusion at the interface between solder alloy and Cu pad. The composition of the IMCs in the solder joints and elemental distribution across the joint interfaces were quantitatively measured with EPMA (electron probe micro analysis). Finally, it was found that the crack initiation point and its propagation path could be influenced by the thermal shock conditions, two underfills, and their properties. This paper was recommended for publication in revised form by Associate Editor Chongdu Cho Kyoung Chun Yang received his B.E. and M.E. degrees in Mechanical Engineering from Chung-Ang University, Korea, in 2006 and 2008, respectively. His research interests include reliability in electronic packages, micro joints evaluation, advanced IC packaging/assembly technologies. Seong Hyuk Lee received his Ph. D. degree in Mechanical Engineering from Chung-Ang University, Korea, in 1999. Dr. Lee is currently an Associate Professor at the School of Mechanical Engineering of Chung-Ang University in Seoul, Korea. His research interests are mainly in the micro/nanoscale energy conversion and transport, the computational physics associated with thin film optics, and thermal and fluid engineering. Jong-Min Kim received his B.E. and M.E. degrees in Mechanical Engineering from Chung-Ang University, Korea, in 1997 and 1999, respectively. He then received his Ph.D. degree in Manufacturing Science from Osaka University, Japan, in 2002. Dr. Kim is currently an Associate Professor at the School of Mechanical Engineering at Chung-Ang University in Seoul, Korea. He has been mainly engaged in the fields of the interconnection & packaging technology in microelectronics and the intelligent assembly process in micro/nano systems. Young Ki Choi received his B.E. and M.E. degrees in Mechanical Engineering from Seoul National University, Korea, in 1978 and 1980, respectively. He then received his Ph.D. degree in Manufacturing Science from Univ. of California, Berkeley, U.S.A., in 1986. Dr. Choi is currently a Professor at the School of Mechanical Engineering at Chung-Ang University in Seoul, Korea. He has been mainly engaged in the fields of the heat transfer in micro-nano systems and the numerical analysis of the heat transfer system. Dave F. Farson received B.S. and M.S. degrees in Welding Engineering and Ph.D. degree in Electrical Engineering from The Ohio State University in 1987. He worked at Westinghouse R&D and Applied Research Laboratory at Penn State University before returning Ohio State University in 1995, where he is currently an Associate Professor in the Department of Integrated Systems Engineering. He is a past-president and Fellow of the Laser Institute of America and was co-editor of its Handbook of Laser Materials Processing. He is also active in the American Welding Society. He does research in laser materials processes and materials joining for a range of applications including biomedical and electronics device fabrication. Young Eui Shin received his B.E.degree Mechanical Engineering from Chung-Ang University in Korea, and M.S and Ph.D degrees from Nihon Univ. and Osaka Univ. in 1985 and 1992 respectively. He worked as principal researcher in the Technical central lab of Daewoo Heavy industry from 1985 to 1988, and as a chief researcher in Technical Center of Samsung Electronics from 1992 to 1994. At present, he is a Professor at the School of Mechanical Engineering, Chung-Ang Univ., in Korea. He is also working as President, Korea Micro Joining Association. He has been mainly engaged in eco friendly materials application for micro system packaging and reliability evaluation for micro joints.     

Feature selection for automatic visual inspection of solder joints

In this paper, three successive feature reduction methods are employed to select good features for the automatic visual inspection of solder joints. This reduction strategy includes (1) a stability test to remove the features with unstable performance, (2) a separability examination to select the features with good classification capabilities, (3) a correlation analysis to delete the redundant features. Three sets of features are implemented in this feature reduction work: (1) a circular sub-area feature set is related to the intensity conditions within distinct areas in the joint image, (2) a moment of inertia feature set is based upon the intensity of pixels and their relative position in the image plane, (3) a surface curvature feature set analyses the three-dimensional joint topology. Initially 50 features are formulated based on the above strategy. The reduction technique deletes 39 features from this set because of instability, poor performance, and high correlation with other features. Finally, the remaining 11 feature are tested and shown to be superior to state-of-the-art identification methods.     

Detection of solder bump defects on a flip chip using vibration analysis

Flip chips are widely used in microelectronics packaging owing to the high demand of integration in IC fabrication. Solder bump defects on flip chips are difficult to detect, because the solder bumps are obscured by the chip and substrate. In this paper a nondestructive detection method combining ultrasonic excitation with vibration analysis is presented for detecting missing solder bumps, which is a typical defect in flip chip packaging. The flip chip analytical model is revised by considering the influence of spring mass on mechanical energy of the system. This revised model is then applied to estimate the flip chip resonance frequencies. We use an integrated signal generator and power amplifier together with an air-coupled ultrasonic transducer to excite the flip chips. The vibrations are measured by a laser scanning vibrometer to detect the resonance frequencies. A sensitivity coefficient is proposed to select the sensitive resonance frequency order for defect detection. Finite element simulation is also implemented for further investigation. The results of analytical computation, experiment, and simulation prove the efficacy of the revised flip chip analytical model and verify the effectiveness of this detection method. Therefore, it may provide a guide for the improvement and innovation of the flip chip on-line inspection systems.     

Some aspects of using piezoelectric probes for ultrasonic inspection of thin welded joints

The choice of parameters of dedicated piezoelectric probes is considered with allowance for a surface wave arising at probe angles close to the second critical angle. Recommendations are given for the choice of optimal probe angles and probe x-values. Examples are given to show the application of the dedicated probes, the choice of their type, and the parameters (frequency, probe angle, x-value) for the inspection of butt-welded joints of tubes on the heating surfaces of boilers at thermoelectric power stations.     

Reliability of ultrasonic inspection of welded joints with incomplete structural fusion

A correlation is established between the depths of incomplete-fusion areas along the surfaces of welded flanges in T-joints and incomplete structural fusion. A rejection level is chosen for the echo-signal amplitude that makes it possible to decrease errors in ultrasonic testing.Translated from Defektoskopiya, Vol. 40, No. 9, 2004, pp. 38–41. Original Russian Text Copyright © 2004 by Konovalov.     

基于改进UNet网络的金丝球焊直径测量研究

提出了一种基于改进UNet网络的金丝球焊焊点精确分割与测量的新方法。改进UNet网络由编码器和解码器两部分构成,其中编码器主要用来提取图像特征,使用在ImageNet数据集上预训练分类网络的卷积模块权重初始化编码器部分,可以在不增加训练数据的情况下,加速网络训练且避免过拟合;解码器主要是结合深层特征和浅层特征以实现精确分割,使用改进的多尺度卷积模块替换原网络中的单尺度卷积模块,使解码器能综合利用不同感受野的特征,进一步提升网络的分割精度。实验结果表明,改进UNet网络与原始UNet网络相比,其测试集分割交并比和F分数分别提升了2.04%和1.58%,且直径测量平均误差从7.734μm降低到1.435μm,满足实际检测需求。     

印刷电路板无铅焊点假焊的检测

通过分析由三色LED环形结构光源和3-CCD彩色相机获取的印刷电路板(PCB)焊点图像特征,设计了一种PCB无铅焊点假焊的检测方法,以提高自动光学检测系统检测焊点质量的准确率,降低误判.该方法通过对焊点及其元器件的定位,采用重心法检测假焊;根据焊点及元器件的边缘确定焊点区域及元器件区域,采用面积法二次检测假焊;最后,采...     

基于BP神经网络的冷轧带钢表面质量检测研究

针对传统的方法在冷轧带钢表面缺陷图像模式识别中存在的问题,在小波变换提取特征的基础上,提出了基于BP神经网络的非线性模式识别方法.结合国内实例,对5种典型冷轧带钢表面缺陷图像进行了实验研究,实验结果表明,该方法能够对冷轧带钢表面缺陷图像进行有效识别,具有更好的适应性.     

电子元件焊接质量的自动光学检测系统研究

为满足表面贴装电子元件的高密度化、小型化、零缺陷等要求,设计一种电子元件焊接质量的自动光学检测系统,可将缺件、多锡、少锡、假焊等焊接缺陷检查出来。该系统首先通过图像采集系统获取电路板图像,并提取元件的检测窗口,通过图像处理得到相应的图像特征,对其特征进行尺寸的测量和识别,然后与标准数据进行比较,判断元件表面焊接质量是否合格,以达到检测元件的目的。系统具有运行平稳、操作方便、智能化和模块化等特点,满足实际生产的需要。     

无铅焊点检测光源的分析与优化设计

为了提高自动光学检查(AOI)系统的性能,对AOI光源进行了研究.介绍了AOI光源的结构设计方法.光源由红、绿、蓝3种不同颜色,不同照射角度的LED阵列组成.然后.建立了光源的照度模型以及焊点的反射模型.最后,根据简化的照度模型对光源的几何参数进行优化.仿真和实验结果表明,所设计的光源在检测无铅焊点时同样有效.并能使不同类焊点间的特征距离更大.最大为半球形光源照射下的11.88倍.从而提高了特征在无铅焊点缺陷检测的分辨能力.验证了光源设计的有效性.     

印刷电路板焊点的智能检测

为了提高在线自动光学检测系统(AOI)的自动化程度,提出了一种基于增量聚类的智能焊点检测方法.首先,设计了在线智能AOI的系统框架.然后,根据焊点外观进行归纳分类,将关键子区域的面积特征应用于焊盘特征的量化与提取,将每类样本聚类为若干子类从而实现对多批次焊点的检测.最后,提出一种增量聚类算法,在线检测过程中系统可根据人...     

PCB焊点及芯线端头识别

智能微型化的医用器械在医疗行业逐渐被人们所重视。这些产品主要是由一些微型电子元器件构成,其中器件核心芯片部分的点线连接结构需通过高精密焊接工作完成。因此焊点和被焊芯线的识别精度要求越来越高,两者是否能准确有效识别直接影响焊接的最终质量。为高质量完成焊接过程中的焊点和芯线识别,本文主要使用电子显微仪器结合上位机VS17+OpenCV软硬结合的方法完成图像处理,对所采集图像中的焊点和芯线端头进行识别。以焊点和芯线端头的颜色及几何特征作为分析对象,经预处理后再通过各自特征分析突出感兴趣区域部分,通过特定颜色阈值选取方式和对比度提升算法完成焊点和芯线端头的分割过程,要求所测量焊点及芯线端头的识别精度误差≤0.1 mm。实验结果表明：本文印刷电路板(PCB)焊点及芯线端头的识别算法能有效识别焊点及芯线端头图中所在位置并显示其像素坐标值;经数据整理分析,本文算法的识别精度误差均控制在允许的误差范围内。     

Automatic ultrasonic inspection of large-diameter pipes

A device and a principle of operation of some ultrasound scanners-flaw detectors for diagnosing the basic metal mass of main oil and gas pipelines in reinsulation is considered. Different methods, materials, and devices for efficient excitation and reception of ultrasound waves in pipelines with wall thicknesses of 6–20 mm and the selection of Lamb and Rayleigh wave modes for testing as a function of the pipe-wall thickness are discussed. The principle of operation of a unidirectional primary EMA transducer is described.     

SMT片式元件焊点三维质量信息提取技术

为实现对表面组装焊点三维质量信息的非接触式提取,提出了一种基于阴影恢复形状原理表面组装片式元件焊点三维质量信息提取方法.为提高重构精度,光照模型采用作者前期研究结果得到的一种改进模型;为解决由阴影恢复形状方法得到的物体三维形态不确定的问题,利用量块得到图像象素值与实际高度的比例关系,以此来确定表面组装焊点的三维形态;采用APDL语言,在ANSYS软件中二次开发建立焊点实体模型,并对相应的焊点体积、剖面面积、润湿角度等三维质量信息进行提取.结合实例介绍了该技术的实现方法与步骤.与采用传统光照模型相比,采用改进光照模型能较好地提高焊点体积信息提取的精度.     

Dynamic behavior of capillary-driven encapsulation flow characteristics for different injection types in flip chip packaging

This study investigated the influence of different injection types, such as I-type, L-type, and U-type, on the dynamic behavior of capillary-driven encapsulation flows for a commercially available flip chip. The dynamic filling behavior of underfill encapsulation was visualized experimentally, and numerical simulations were conducted for three-dimensional flows in a flip chip package by using commercial software (ANSYS FLUENT Ver. 13.0). Numerical results were compared with experimental data for the filling time and the rate of change in underfill volume fraction with different injection types. At the early stage of underfill injection, the estimated flow characteristics exhibited high capillary acceleration that rapidly decreased with time, which indicates that capillary force was dominant in underfill encapsulation. The capillary pressure drop effect was dominant at the early stage. Thus, the injection method for underfill encapsulation inside the flip chip should be carefully controlled for faster and more stable encapsulation to avoid void formation in the chips.     

Dedicated optical instruments for ultrasonic welder inspection and control

Two different optical instruments for real-time vibration measurements, inspection and control of ultrasonic welders were designed, realized and characterized: a self-mixing laser interferometer and an optical triangulator, both studied for achieving high bandwidth and very good resolution within a short dynamic range. The implemented instruments can solve the problem of measurement and control of ultrasonic welders that until now has no low-cost solutions available on the market. The performance of the two developed instruments was compared in order to assess which is the most appropriate for this specific application. Finally, results of the real-time characterization of an ultrasonic welder are given and discussed.     

结合面法向和切向接触刚度的MPSO-BP神经网络算法的建模

提出一种基于改进的粒子群和BP神经网络相结合的算法模型,用改进粒子群优化算法优化BP神经网络参数。以机械结合面法向接触刚度和切向接触刚度作为算例。考虑结合面配对副材料、接触载荷、表面加工方法、表面粗糙度和结合面间的介质作为主要因素,对8组结合面法向和切向接触刚度进行预测建模,并对仿真与实验结果进行比较与误差分析。结果表明,该方法实现了多种影响因素组合下的机械结合面法向和切向接触刚度较高精度的建模和预测。     

Evolution of micro solder joints under electromigration and elastic field

This paper proposes a three-dimensional model for the evolution of micro and sub-micro scale flip chip solder joints. The coupled mechanisms of electromigration and the corresponding stress gradient are incorporated into a diffuse interface model. A semi-implicit Fourier spectral method and the preconditioned biconjugate-gradient method are proposed for the computation to achieve high efficiency and numerical stability. Our simulations demonstrate dynamic evolution of solder joints and breakages at the interface on the cathode side. It is also shown that the dynamically incorporated stress gradient considerably affects the evolution of solder joints counteracting the electromigration process. This paper was recommended for publication in revised form by Associate Editor Jeonghoon Yoo Dongchoul Kim received a B.S. degree in Mechanical Engineering from Yonsei University in 2000. He then went on to receive his M.S. and Ph.D. degrees from The University of Michigan in 2003 and 2005, respectively. Dr. Kim is currently an Assistant Professor at the School of Mechanical Engineering at Sogang University in Seoul, Korea. His research interests are in the area of computational analysis of micro/nanostructures.     

PCBA 板载 DDR 芯片焊点缺陷检测研究

板载芯片朝着小尺寸高密度方向发展,隐藏于芯片封装内部的微焊球缺陷检测愈发困难。针对工业高密度集成印刷电路板组件(PCBA)板载集成电路(IC)内部故障定位难、效率低的问题,提出一种芯片功能测试过程中采用红外热成像检测结合深度学习的多类型缺陷识别方法。以现场可编程门阵列(FPGA)单板双倍数据速率(DDR)存储芯片为对象,建立了芯片缺陷检测模型,搭建检测平台开展芯片内部焊点故障检测试验研究。设计程序实现芯片的数据存储与读出,同步采集红外图像序列,分析存储芯片读写过程中温度变化,并提取不同敏感测量区域热信号。构建卷积神经网络(CNN)分类模型,并进行超参数调优,实现了内部隐藏缺陷包括不同地址、数据、地址空间焊点故障的高效准确识别。引入迁移学习拓展应用于芯片其他9种不同焊点缺陷的检测,在10、20 dB高斯白噪声条件下分别达到95%、92%以上的准确率,从而为实际工业高密度集成PCBA板载微电子封装及可靠性分析提供了一种快速、有效的方法。