【作者】 陆向宁；

【导师】 史铁林； 廖广兰；

【作者基本信息】 华中科技大学 ， 机械制造及自动化， 2012， 博士

【摘要】 芯片互连是微电子封装的关键技术之一,而倒装焊采用凸焊点实现芯片与基底之间的机械和电气连接,因封装尺寸小、信号传输速度快等优点已逐渐成为微电子封装的主流工艺。随着倒装芯片凸点密度的提高及其间距的进一步减小,芯片的功率密度将迅速增加,芯片的散热和内部热应力失配问题更加严重,易于发生键合失效。由于凸点或焊球隐藏于芯片和基底之间,其热性能分析及缺陷检测变得更加困难。为此,本文将主动红外无损检测技术应用于微电子封装领域,结合有限元仿真对焊球热性能及缺陷检测进行了研究和分析,主要研究内容如下：利用解析和数值仿真方法分析了倒装芯片内部焊球的导热性能。建立了倒装焊结构的热传导数学模型,并给出了解析求解过程。将常见焊球缺陷引入倒装芯片的热传导模型,建立了倒装焊结构的纵向热阻网络；采用有限元法仿真分析了外部热激励作用下的倒装焊内部热传导状况,对比分析了缺陷焊球与参考焊球对应的温度变化。通过计算获得了存在裂纹或空洞的缺陷焊球与正常焊球各自的热阻阻值,并进一步研究了焊球热阻与缺陷尺寸之间的关系。倒装焊内部热传导分析及焊球热性能表征为主动红外缺陷检测提供了参考依据和评估指标。研究了主动红外热成像检测原理、方法及系统组成,并根据倒装芯片特点和检测要求,提出了一种基于主动红外热成像的倒装焊缺陷检测方法,设计并构建了实验检测平台。采用光纤耦合半导体激光器对芯片或基底表面进行非接触式加热,通过红外热像仪获得芯片表面温度分布及随时间的变化,通过热图像信号处理提取特征量,对焊球缺陷进行诊断与辨识。主动红外热成像检测系统构建及方法研究为开展倒装焊缺陷检测提供了实验平台和热图像解析的理论基础。利用主动红外检测实验平台,对不同尺寸焊球的缺陷检测展开实验研究。采用双面测量法对焊球直径为500μM的自制样片S1进行了缺陷检测实验,通过热图像的空间自适应滤波、边缘检测及图像分割等方法,消除了热图像噪声及焊球间隙对缺陷辨识的影响,并使用焊球的热斑面积及其温度直方图对焊球缺陷进行定量分析；采用双面测量法对焊球直径为300μm的自制样片S2进行了缺陷检测实验,通过移动平均滤波去除热图像序列中的随机噪声,构建了加热源能量分布图,并采用自参考对比法,使用焊球热斑边缘点与UBM区中心点的温差累积值对焊球状况进行判别,消除了加热不均匀性对缺陷辨识的影响,实现了焊球缺陷的有效检测；采用单面测量法对焊球直径为135μm的选购样片FA10进行了缺陷检测实验。通过自适应中值滤波及移动平均滤波算法对热图像序列进行空间和时间域上的平滑和去噪,并对热图像中各点的温度序列值按指数形式进行曲线拟合。为了减小发射率差异及加热不均匀性的影响,采用脉冲相位法,通过傅里叶变换将时域温度信息转换为频域相位信息,使用低频段的相位图进行缺陷辨识,从而实现了缺失焊球的有效检测。本文采用主动红外检测方法实现了缺失焊球的有效检测,并将其检测范围扩展应用于BGA、CSP等表面安装器件的焊球缺陷检测,为高密度微电子封装的可靠性评估提高了一种快速、有效的方法。更多还原

【Abstract】 Chip interconnection is one of the key technologies for microelectronic packaging. The flip chip, which uses solder bumps to realize interconnection between chips and substrates, becomes the mainstream technics in microelectronic packaging because of its decreased package size, larger speed of signal propagation and so on. With the development of solde bumps towards higher density and finer pitch, the chip power density will increase dramatically, and the heat dissipation will become a significant problem, the thermal mismatch in the package is also getting serious, which results in solder defects and bonding failures. Defects inspection and characterization of the thermal perfermence for the solder bumps are more difficult as the bumps are hidden in flip chip package. The active infrared thermography technology was applied to defects inspection in microelctronic packaging in this thesis, and the finite element method was also adopted to investigate the heat conduction in the flip chip.The thermal performance of the solder bumps was investigated using the analytical and numerical methods. We constructed a mathematical model for heat transfer in the flip chip structure and provided the solving procedure. A lumped thermal resistance network was derived from the one dimension heat transfer model to which common defects were introduced. The heat conduction in the flip chip was analysed using numerical simulation. The thermal performance of the solder bumps was characterized by using the thermal resistances. The thermal resistances of the reference bump and defective bump were calculated respectively and the relationship between the thermal resistance and the defects size was also studied. The analysis of heat conduction in flip chip and the thermal characterization of the solder bump provide a criterion for package reliability evaluation and defects inspection.We have studied the principle and methods for the active infrared thermography. A novel approach for defects inspection of the solder bumps based on the active infrared thermography technology was proposed and the experimental setup was constructed, in which surface of the die or substrate is heated by the fiber coupled diode laser, and the temperature distribution on the top surface of the die is monitored by the thermal imager. Then the soder defects are distinguished by some characterisctic quantities derived from the thermography processing, which makes the experiments of defects inspection feasible, and offers a guideline for thermography interpretation.Experiments have been carried out to inspect the missing solder bumps of different diameter and pitch. The test vehicle S1 with the solder bumps of 500μm in diameter was detected in transmission way. Techniques of the adaptive filtering, the edge detection and the image segmentation were adopted to decrease the noise in thermograms and to eliminate the influence of emissivity difference between the UBM layer and gaps. The hotspot area over every solder bump and the temperature histogram are used to characterize the defects quantificationally. The test vehicle S2 with the solder bumps of 300μm in diameter was also detected in transmission way. The moving average filter was used to remove the random noise. The source distribution image was created to indicate the spatial nonuniformity of excitation. IR self reference method was proposed that temperature value of every edge point is substract from that of the central point at each time, and the temperature difference was accumulated all time. The defective solders are differentiated by the summation of the temperature difference. The specimen FA 10 with the solder bumps of 135μm in diameter was inspected in reflection way. The spacial and temporal filtering techniques were adopted to improve the signal to noise ratio. The recorded thermograms were input into an adaptive median filter, and the temperature evolution of each pixel was extracted and smoothed by the moving average operation. Then the temperature-time curve was fitted with an exponential function. To eliminate emissivity variations and heating non-uniformity, we converted the fitted temperature values in time domain to the phase information in frequency domain using fast Fourier transform. The defective solder bumps were indentified in the phase map at low frequency.The results demonstrate that the active infrared thermography technology is effective for identification of the missing bumps, and can also be used for inspection of solder balls in CSP and BGA packages, which provides a fast and effective method for reliability evaluation in high density packaging.更多还原