As the carrier of various components and the hub of circuit signal transmission, PCB 已成为电子信息产品中最重要、最关键的部分，其质量和可靠性水平决定了整个设备的质量和可靠性。 然而，由于成本和技术原因，PCB生产和应用中存在很多故障问题。

对于这种失效问题，我们需要使用一些常用的失效分析技术来保证PCB在制造过程中的质量和可靠性水平。 本文总结了十种失效分析技术以供参考。

PCB故障机理及原因分析

1. 目视检查

外观检查是用肉眼检查或使用一些简单的仪器，如立体显微镜、金相显微镜甚至放大镜，检查PCB的外观，找出不合格零件和相关物证。 主要作用是定位故障，初步判断PCB的故障模式。 外观检查主要检查PCB污染、腐蚀、电路板爆炸的位置、电路布线和故障的规律性，是批量还是个别，是否总是集中在某个区域等。 In addition, the failure of many PCBS was discovered after the assembly of PCBA. Whether the failure was caused by the influence of the assembly process and materials used in the process also requires careful examination of the characteristics of the failure area.

2. X 射线透视

对于一些外观无法检测的部分，以及PCB内部通孔等内部缺陷，我们必须使用X射线透视系统进行检查。 X射线透视系统是利用不同材料厚度或不同材料密度的X射线吸湿性或透射率不同的原理来成像的。 该技术更多用于检查PCBA焊点缺陷位置、通孔缺陷以及高密度封装的BGA或CSP器件缺陷。 At present, the resolution of industrial X-ray fluoroscopy equipment can reach less than one micron, and is changing from two dimensional to three dimensional imaging equipment. There are even five dimensional (5D) equipment used for packaging inspection, but this 5D X-ray fluoroscopy system is very expensive, and rarely has practical application in the industry.

3. 截面分析

Slice analysis is the process of obtaining PCB cross section structure through sampling, Mosaic, slice, polishing, corrosion, observation and a series of methods and steps. Abundant information about the microstructure of PCB (through hole, coating, etc.) can be obtained by slice analysis, which provides a good basis for the next quality improvement. However, this method is destructive, once the slice is carried out, the sample will inevitably be destroyed; 同时，对样品的方法要求高，样品制备时间也长，需要经过培训的技术人员才能完成。 For detailed slicing procedures, please refer to IPC standards IPC-TM-650 2.1.1 and IPC-MS-810.

4. 扫描声学显微镜

At present, c-mode ultrasonic scanning acoustic microscope is mainly used for electronic packaging or assembly analysis. It makes use of the amplitude, phase and polarity changes generated by the reflection of high-frequency ultrasound on the discontinuous interface of materials to image, and its scanning mode is to scan the information in the X-Y plane along the Z-axis. Therefore, scanning acoustic microscopy can be used to detect various defects, including cracks, delamination, inclusions, and voids, in components, materials, and PCB and PCBA. Internal defects of solder joints can also be directly detected if the frequency width of scanning acoustics is sufficient. Of a typical scanning acoustic image in color red alert said defects exist, because a large amount of plastic packaging components used in SMT process, by a lead into the process of lead-free technology, a large number of moisture reflow sensitive problem, namely the moisture absorption of powder coating devices will be at a higher temperature reflow lead-free process occurs within or substrate layer cracking phenomenon, Under the high temperature of lead-free process, common PCB will often burst board phenomenon. 至此，扫描声学显微镜在多层高密度PCB无损检测中显示出其特殊的优势。 The general obvious bursting plate can be detected by visual inspection.

5. 微红外分析

显微红外分析是将红外光谱结合显微镜分析的方法，它利用不同物质（主要是有机物）的红外光谱吸收原理，分析物质的化合物成分，再加上显微镜可以使可见光和红外光有了光路，只要在视野下，就可以寻找分析微量有机污染物。 在没有显微镜的情况下，红外光谱通常只能分析大样品。 In many cases, trace pollution in electronic process can lead to poor weldability of PCB pad or lead pin. It can be imagined that it is difficult to solve the process problem without the matching infrared spectrum of microscope. The main use of microscopic infrared analysis is to analyze the organic pollutants on the welding surface or solder spot surface, and analyze the causes of corrosion or poor solderability.

6. 扫描电镜分析

扫描电子显微镜 (SEM) 是用于故障分析的最有用的大型电子显微成像系统之一。 其工作原理是将阴极发射的电子束经阳极加速后聚焦，形成直径为数十至数千埃（A）的电子束。 在扫描线圈偏转的作用下， 电子束按一定的时间和空间顺序逐点扫描样品表面。 高能电子束轰击样品表面，产生多种信息，经采集放大后，在显示屏上得到各种相应的图形。 The excited secondary electrons are generated within the range of 5 ~ 10nm on the surface of the sample. Therefore, the secondary electrons can better reflect the surface topography of the sample, so they are most commonly used for morphology observation. 激发后的背散射电子在样品表面产生100～1000nm范围内，随着物质原子序数的不同，发射出不同的特性。 因此，背散射电子图像具有形态特征和原子序数辨别能力，因此，背散射电子图像可以反映化学元素的分布。 现在的扫描电子显微镜已经非常强大了，任何细微的结构或表面特征都可以放大到数十万倍进行观察和分析。

In PCB or solder joint failure analysis, SEM is mainly used for failure mechanism analysis, specifically, is used to observe the surface morphology structure of the pad, solder joint metallographic structure, measurement of intermetallic compounds, solderable coating analysis and tin must be analyzed and measured. Different from the optical microscope, the scanning electron microscope produces electronic images, so it has only black and white colors. Moreover, the sample of the scanning electron microscope is required to conduct electricity, and the non-conductor and part of the semiconductor need to be sprayed with gold or carbon, otherwise the charge will gather on the surface of the sample and affect the sample observation. 此外，扫描电镜图像的景深远大于光学显微镜，是分析金相组织、显微断口和锡须的重要方法。

7. X-ray energy spectrum analysis

上述扫描电子显微镜通常配备有X射线能谱仪。 When the high-energy electron beam hit the surface, the surface material of the inner electrons in the atoms are bombarded escape, outer electrons to low energy level transition will inspire characteristic X ray, atomic energy level difference of different elements from different characteristic X ray is different, therefore, can send sample of the characteristics of X-ray as chemical composition analysis. 同时，相应的仪器根据X射线信号检测的特征波长或特征能量分别称为光谱色散光谱仪（简称WDS）和能量色散光谱仪（简称EDS）。 光谱仪的分辨率比能谱仪高，能谱仪的分析速度比能谱仪快。 由于能谱仪速度快、成本低，一般的扫描电镜都配备能谱仪。

电子束扫描方式不同，能谱仪可以对表面的点、线、面进行分析，得到不同元素分布的信息。Point analysis yields all elements of a point; 线分析 每次对指定的线进行一个元素分析，通过多次扫描得到所有元素的线分布。 表面分析 对给定表面中所有元素的分析。 测量的元素含量是表面测量范围的平均值。

In the analysis of PCB, energy dispersive spectrometer is mainly used for the composition analysis of pad surface, and the elemental analysis of contaminants on the surface of pad and lead pin with poor solderability. 能谱仪定量分析精度有限，含量低于0.1%一般不易检测。 能谱和扫描电镜结合可以同时获得表面形貌和成分的信息，这也是它们被广泛使用的原因。

8. 光电子能谱 (XPS) 分析

样品经X射线照射，原子内壳层电子表面会脱离原子核与固体表面形成的束缚，测量其动能Ex，可得到原子内壳层电子的结合能Eb、Eb 因不同元素和不同电子壳层而异，它是原子识别参数的“指纹”，谱线的形成就是光电子能谱（XPS）。 XPS可用于样品表面浅表层（几纳米）元素的定性和定量分析。 此外，可以从结合能的化学位移获得有关元素化学价态的信息。 它可以给出表面层的价态与周围元素之间的键合信息。 The incident beam is X-ray photon beam, so insulation sample analysis can be carried out, without damaging the analyzed sample rapid multi-element analysis; Multilayers can also be analyzed longitudinally by argon ion stripping (see the case below) with far greater sensitivity than energy spectrum (EDS). XPS主要用于PCB涂层质量分析、污染分析和氧化程度分析，以确定可焊性差的深层原因。

9. Differential Scanning Calorim-etry

一种在程序温度控制下测量物质和参比物质之间功率输入差异作为温度（或时间）函数的方法。 DSC is equipped with two groups of compensation heating wire under the sample and reference container, when the sample in the heating process due to the thermal effect and reference temperature difference δ T, through the differential heat amplifier circuit and differential heat compensation amplifier, so that the current flowing into the compensation heating wire changes.

The temperature difference δ T disappears, and the relationship between the difference of the thermal power of the two electrically compensated samples and the reference material with temperature (or time) is recorded. According to this relationship, the physicochemical and thermodynamic properties of the material can be studied and analyzed. DSC is widely used in PCB analysis, but is mainly used to measure the curing degree of various polymer materials used in PCB and glass state transformation temperature, these two parameters determine the reliability of PCB in the subsequent process.

10. Thermomechanical analyzer (TMA)

Thermal Mechanical Analysis is used to measure the deformation properties of solids, liquids and gels under Thermal or Mechanical forces under programmed temperature control. Commonly used load methods include compression, pin insertion, stretching, bending, etc. Test probe consists of fixed on the cantilever beam and helical spring support, through the motor of the applied load, when the specimen deformation occurs, differential transformer to detect the change, and together with the data processing, such as temperature, stress and strain after the material can be obtained under the negligible load deformation relations with temperature (or time). According to the relationship between deformation and temperature (or time), the physicochemical and thermodynamic properties of materials can be studied and analyzed. TMA is widely used in PCB analysis and is mainly used in measuring the two most critical parameters of PCB: linear expansion coefficient and glass transition temperature. 膨胀系数过大的PCB在焊接组装后，往往会导致金属化孔的断裂失效。