高温存储下不同成分Sn-Pb凸点可靠性研究

随着我国集成电路封装密度的不断提高,引线键合方式已无法满足需求,倒装焊技术逐渐成为高密度封装主流方向。高温存储对倒装焊凸点的可靠性有着重大影响,界面化合物及晶粒形态均会发生显著变化。以多种SnPb凸点为研究对象,分析高温存储对凸点可靠性的影响,结果表明:10Sn90Pb凸点剪切强度波动幅度较小;Sn含量越高,高温存储后焊料界面处IMC层越厚,63Sn37Pb焊料界面IMC变化最为明显;63Sn37Pb凸点IMC生长速度较快,晶粒粗化现象较为严重。     

Sn-3.5Ag合金在Cu,Ni倾斜基板的润湿及界面特性

良好的润湿性是优质焊料的重要指标,同时也可以为复合无铅焊料的开发提供必要的研究基础。而工业过程中的操作表面往往是倾斜的,因此,研究倾斜状态下的润湿特性更能反映实际情况。本文采用静滴法研究了不同温度下Sn-3.5Ag合金熔体在Cu,Ni材料水平基板和倾斜基板上的润湿行为与界面相互作用,分析了润湿机理。结果表明,Sn-3.5Ag合金与固体Cu基板在(494～744)K时的平衡接触角为139.2°～33.3°,接触角滞后为82.1°～47.8°。Sn-3.5Ag合金与固体Ni基板在(494～744) K时的接触角分别为140.8°～41.5°,接触角滞后为92°～60.9°。在不同温度下Sn-3.5Ag合金熔体在不同温度下与固体Cu基板之间有良好的润湿性且为反应性润湿。Sn-3.5Ag熔体与基板Cu之间的界面产物是由Cu_6Sn_5及Cu_3Sn所组成。用三相界面平衡的界面张力关系式分析了Sn-3.5Ag合金与Cu基板的三相界面,符合较好。Sn-3.5Ag对Ni基板的润湿过程也是反应性润湿。     

煤炭燃烧过程中重金属迁移及控制规律的热力学模拟

选择对人体和环境危害程度较大的有害元素汞(Hg)、铅(Pb)和铬(Cr)作为研究对象,利用FactSage软件模拟煤炭燃烧过程中温度、压力对3种重金属的迁移情况并探究若干种元素及化合物对其控制作用影响。结果表明,温度较压力对重金属迁移影响更为显著。Hg在燃烧全程以不同形态接近100%的迁移量进入气相;Pb在850℃开始大量迁移;Cr在1150℃产生迁移趋势。从热力学角度Hg无法被固定;Pb会与Al_2O_3形成高熔点的化合物得到有效抑制;Cr与碱金属、碱土金属形成高熔点的化合物被赋存在固相或液相中,MnO对Cr也存在间接抑制作用。3种重金属对Cl元素尤为敏感,高氯煤的燃烧除了其本身存在污染外势必会与重金属形成低沸点化合物产生强烈气相迁移并造成进一步的生态破坏。     

石蜡热膨胀性能试验装置的研究

在微机电系统中,为了兼顾作用力强和形变量大两者的统一,采用以石蜡作为热膨胀材料的热驱动方式.介绍了水浴加热石蜡热膨胀性能试验装置,试验结果表明:石蜡在其熔点温度附近,试验中所用石蜡当温度从37℃升高到51℃时,其体膨胀系数可以达到甚至超过10%,而且,作用力大;不同成分(C原子)比例的石蜡,其熔点温度变化范围为30～70℃,这使驱动器在不允许有较大温度变化的环境中(如人体内)使用成为可能.     

使用电烙铁的焊接方法

电烙铁是电子电路制作、调试、维修中不可缺少的焊接工具。一般使用25W内热式,采用“握笔式”握法(如图1)进行焊接。 1.焊接、焊剂的选用: 电子制作常用锡铅合金焊料,一般制成空心焊锡丝,芯内贮有松香。这种焊料熔点低、凝固迅速、强度较好。焊剂则用松香或松香酒精     

无铅焊点蠕变电阻测试系统的研制

以Sn-3.5Ag焊料制作的截面积1 mm2的单个焊点试样为测试对象,基于电阻应变与裂纹生长等效模型,利用在线四探针法电阻测量技术,研制了焊点蠕变电阻测试系统.系统由测试仪、测试装置和上位机软件creep组成,实现微电阻、拉力、温度测量和测试数据的实时存储、实时应变曲线的绘制.测试结果表明:系统具有较高的稳定性,电阻测量最大相对误差为0.27%.在20-29MPa应力范围下,Sn-3.5Ag焊点试样的电阻应变-时间测试曲线清晰地展示了剪切蠕变行为的第Ⅱ,Ⅲ阶段,为观测无铅焊点剪切蠕变特性提供了一种高效、简捷的可选手段.     

黑体式蓝宝石光纤高温计的研究

蓝宝石(单晶氧化铝)具有高达2050℃的熔点,而且在接近其熔点时仍能在可见光和近红外光区保持透明和不辐射.1984年,R.R.Dils研制的黑体式蓝宝石光纤高温计适用     

等温时效过程中锡银铜焊料合金的断裂模式演变

对锡银焊料和锡银铜焊料与铜衬底经钎焊方法焊接后,在焊点界面和焊料内部形成的金属化合物进行研究。通过扫描电镜观察,在150时效后,焊料接头的断裂模式演变。结果表明：随着铜从无到有的增加,无铅互连的断裂模式从柔韧变化到易碎。由于其特性微观结构不同,铜含量的影响应力走势,但两者趋势不尽相同。     

焊接原理及其可靠性

焊接原理焊接工艺是通过“润湿”及“扩散”两个过程来完成,焊点的可靠性也由这两个过程的完整性来判断。 1.润湿过程熔融的焊料涂覆在铜箔表面后,形成均匀、光滑、不断裂的焊料箔层。焊料借助被焊金属表面毛细管力,沿着金属表面细微的凹凸及间隙四周漫流的过程,称为“润湿”过程。若熔融的焊料涂覆在铜箔表面后,焊料回缩分离,形成不     

纳米碳管中及自由状态下镍团簇形态与熔化的分子动力学研究

采用Rosato-Guillope-Legrand多体势分子动力学方法，模拟了（40，0）纳米碳管中及自由状态下Ni534原子团簇的形态与熔化特性，并对其差异进行了讨论。研究表明，温度T=300K时，碳管中及自由状态下的Ni534都具有晶体特征，但碳管中Ni534团簇的形态为与碳管同轴的单壁Ni管，而自由Ni534团簇为近似球形；碳管中Ni534团簇的熔点在900K以上，而自由Ni534团簇的熔点为696K左右。     

An efficient solder joint defects method for 3D point clouds with double-flow region attention network

In electronics mass-production, image-based methods are often used to detect the solder joint defects for achieving high-quality assurance with low labor costs. Recently, deep learning in 3D point clouds has shown an effective form of characterization for 3D objects. However, existing work rarely involves defect detection for PCBs based on 3D point clouds. In this paper, we propose a novel neural network named double-flow region attention network (DoubRAN) to detect defects of solder joints with 3D point clouds. On the one hand, a binocular lidar system is designed to efficiently capture 3D point clouds of solder joints. On the other hand, a fine-grained method named region attention network (RAN) is designed to detect defects, which attends on the region of interest directly by backpropagation without bounding box annotation. To evaluate the performance of our proposed network, we conduct extensive experiments on a unique dataset built by ourselves. The experimental results show that the region of interest extracted by RAN is consistent with the basis for human evaluation of solder joint quality. Besides, the defect detection results of DoubRAN meet factory requirements.     

High density and through wafer copper interconnections and solder bumps for MEMS wafer-level packaging

This paper proposes an innovative process combining the electroforming of high-density and through-wafer copper interconnections and solder bumps for advanced MEMS packaging. Vias with the diameter of 30 to 100 m were etched through on a 4-inch and 550 m-thick silicon substrate by ICP-DRIE process for an aspect ratio up to 18.3. MRTV1 silicon rubber layer was employed for substrates quickly releasing after copper-interconnections electroforming. Compared to the tedious wet etching or mechanical polishing process, this peel-off relasing process provides a simpler way. After another lithography process, mushroom shape eutecic solder bumps (63Sn/37Pb) were directly electroformed on the top of each copper interconnection with the height of 100 m, and reflowed at 200 °C for 5 min to form solder spheres. The feasibility of making highly dense and uniform electrical interconncetions has been successfully demonstrated on the wafer with fabricated micro temperature sensors. The estimated resistance for the copper-column of different diameters are characterized lower than 13.1 m and this process provides a bump density up to 9648 interconnects/cm².This paper was partially supported by the contract NSC 89–2323-B-007–005, through National Science Council, Taiwan. We also appreciate the help from MicroSystem Common Laboratory at Industrial Technology Research Institute for ICP-DRIE process.     

Electrical and reliability properties of isotropic conductive adhesives on immersion silver printed-circuit boards

Electrically conductive adhesive (ECAs) have been used for many years in both the anisotropic conductive adhesive (ACA) and isotropic conductive adhesive (ICA) forms for microelectronic packaging applications and as an alternative to lead (Pb) soldering technology. Especially, environmentally friendly ICAs offer many advantages over solder, such as simple and low temperature process conditions and better thermo-mechanical performance. However, a number of reliability questions linger, and continue to be studied. In particular, the ICA-to-pad contact resistance can increase with time due to the galvanic corrosion of dissimilar contact and ICA-filler metals (Lu et al., IEEE Trans Electron Packag Manuf 22:228–232, 1999). ICAs are usually silver (Ag) epoxy composites, and the corrosion potential should be completely eliminated by the use of Ag contact pads. To completely eliminate lead (Pb) from electronics, the printed wiring board (PWB) must also change from hot-air-leveled solder (SnPb) to alternative metallic finishes, such as immersion-silver (Ag), immersion-tin (Sn), electroless nickel (Ni)/immersion-gold (Au) and organic solderability preservative (OSP) (Pas, in European institute of printed circuits summer conference, 2005). Especially, immersion-Ag is one of the leading Pb-free final finish choices for many OEMs in the telecommunications, computer, automotive and consumer electronics industries, because of its excellent properties and reasonable cost. This paper presents the electrical properties of Ag epoxy composite ICAs materials on Cu-finished and immersion-Ag finished PWBs, as solder replacements for SMT or flip chip technologies. All PWBs were subjected to 85°C/85% relative humidity (RH) aging testing, with junction resistance monitored for comparison of the immersion-Ag board to the Cu-finished board as a control. We expected that the corrosion potential, which is one of main causes to degrade conductivity between ICAs and PWB, should be eliminated by the use of Ag contact pads with the Ag epoxy composite ICAs materials. Not only is the junction resistance of immersion-Ag finished boards lower than that of Cu finished boards, but its junction resistance changes are smaller than those of Cu-finished boards, as expected.     

An inspection and classification method for chip solder joints using color grads and Boolean rules

In order to improve the comprehensive performance of solder joints inspection in three aspects, i.e. high recognition rate, detailed classification of defect types and fast inspection speed, a new detection and classification algorithm of the chip solder joints based on color grads and Boolean rules is developed in this paper. Firstly, the region features, evaluation features and color grads’ features are defined and extracted based on the special solder joint image, which is acquired by a particular image acquisition system composed of a 3-CCD color digital camera and a 3-color (red, green, and blue) hemispherical LED array illumination. Secondly, the models of solder joint types are built based on extracted features and statistical characteristics of solder joint types. Thirdly, the detection and classification method is designed and presented using Boolean rules, then eight common solder joint types, including the acceptable solder joint, pseudo, no solder, lacked solder, excess solder, shifted, tombstone, and miss component, can be classified and detected by the proposed algorithm. Fourthly, the proposed algorithm is optimized to improve the inspection speed based on a parallel computing method. Finally, to evaluate the performance of the proposed method, 79 pieces of PCBs with defects were inspected by the commercial AOI system developed by the authors which integrates the proposed algorithm. Experiment and result analysis illustrates that the proposed method is better than other methods in three aspects, it can detect and classify properly all the eight common types of solder joints, its detailed classification, and high correct rate, which is up to 97.7%, are more useful to the quality control in the manufacturing process, and its inspection speed is faster, thus helping us to improve the efficiency of the manufacturing process.     

Evaluation of thermo-mechanical damage and fatigue life of solar cell solder interconnections

The soldering process of interconnecting crystalline silicon solar cells to form photovoltaic (PV) module is a key manufacturing process. However, during the soldering process, stress is induced in the solar cell solder joints and remains in the joint as residual stress after soldering. Furthermore, during the module service life time, thermo-mechanical degradation of the solder joints occurs due to thermal cycling of the joints which induce stress, creep strain and strain energy. The resultant effect of damage on the solder joint is premature failure, hence shortened fatigue life. This study seeks to determine accumulated thermo-mechanical damage and fatigue life of solder interconnection in solar cell assembly under thermo-mechanical cycling conditions. In this investigation, finite element modelling (FEM) and simulations are carried out in order to determine nonlinear degradation of SnAgCu solder joints. The degradation of the solder material is simulated using Garofalo-Arrhenius creep model. A three dimensional (3D) geometric model is subjected to six accelerated thermal cycles (ATCs) utilising IEC 61215 standard for photovoltaic panels. The results demonstrate that induced stress, strain and strain energy impacts the solder joints during operations. Furthermore, the larger the accumulated creep strain and creep strain energy in the joints, the shorter the fatigue life. This indicates that creep strain and creep strain energy in the solder joints significantly impacts the thermo-mechanical reliability of the assembly joints. Regions of solder joint with critical stress, strain and strain energy values including their distribution are determined. Analysis of results demonstrates that creep energy density is a better parameter than creep strain in predicting interconnection fatigue life. The use of six ATCs yields significant data which enable better understanding of the response of the solder joints to the induced loads. Moreover, information obtained from this study can be used for improved design and better-quality fabrication of solder interconnections in solar cell assembly for enhanced thermo-mechanical reliability.     

10 t/d Sn-Pb真空脱铅炉的最优控制算法研究

以10t/d焊锡真空蒸馏脱铅炉为研究对象，在已获多变量动态辨识模型基础上，进行了最优控制算法的研究。仿真结果表明，所提出的设定值可变的前馈－比例最优控制算法，对此型真空炉具有良好的控制效果，并为进一步实现优化控制奠定了理论基础。     

Design and development of automatic visual inspection system for PCB manufacturing

Inspection of solder joints has been a critical process in the electronic manufacturing industry to reduce manufacturing cost, improve yield, and ensure product quality and reliability. This paper proposes two inspection modules for an automatic solder joint classification system. The “front-end” inspection system includes illumination normalisation, localisation and segmentation. The “back-end” inspection involves the classification of solder joints using the Log-Gabor filter and classifier fusion. Five different levels of solder quality with respect to the amount of solder paste have been defined. The Log-Gabor filter has been demonstrated to achieve high recognition rates and is resistant to misalignment. This proposed system does not need any special illumination system, and the images are acquired by an ordinary digital camera. This system could contribute to the development of automated non-contact, non-destructive and low cost solder joint quality inspection systems.     

焊点质量检测新方法

提出一种基于小波神经网络的焊点质量检测算法。首先对焊点图像进行预处理,然后提出采用形态因子和曲率作为焊点图像特征,最后建立焊点质量检测的小波神经网络模型。实验结果表明,提出的焊点质量检测算法具有较快的处理速度以及较高的准确率。     

光读出红外成像芯片真空封装研究

为解决光读出红外成像焦平面阵列器件的真空封装,提出了一种新颖的真空封装方法。该封装结构由可见光窗口、硅垫片和红外窗口三部分构成。硅垫片和可见光窗口（玻璃）通过阳极键合形成封装腔体,用于放置芯片;红外窗口不仅选择性增透8～14μm波段的红外辐射,且作为封装盖板;封装腔体和红外窗口在真空室内通过焊料键合完成真空封装。该封装结构通过了气密检测,并测试得到了200℃电烙铁热像图。