As the hub of various components and circuit signal transmission, PCB has become the most important and critical part of electronic information products. Its quality and reliability determine the quality and reliability of the whole equipment. However, due to cost and technical reasons, PCBs have experienced a large number of failures during production and application. For this failure problem, we need to use some common failure analysis techniques to ensure the quality and reliability of the PCB during manufacturing. This paper summarizes the top ten failure analysis techniques for reference. 1. Visual inspection Visual inspection is to visually test or use some simple instruments, such as stereo microscope, metallographic microscope or even magnifying glass to check the appearance of the PCB, find the faulty part and related physical evidence. The main function is to locate the fault and determine the failure mode of the PCB. The visual inspection mainly checks the PCB contamination, corrosion, location of the blasting board, circuit wiring and the regularity of the failure, such as batch or individual, is always concentrated in a certain area and so on. In addition, many PCB failures are discovered after assembly into PCBA. Failures caused by the assembly process and the materials used in the process also require careful examination of the characteristics of the failure zone. 2. X-ray fluoroscopy For some parts that cannot be visually inspected, as well as the inside of the through hole of the PCB and other internal defects, it is necessary to use an X-ray system to check. X-ray system is the use of different material thickness or different material density to image the different principles of X-ray moisture absorption or transmittance. This technique is used more to inspect defects inside PCBA solder joints, via internal defects, and the location of defective solder joints in high-density packaged BGA or CSP devices. The current industrial X-ray equipment has a resolution of less than one micron and is being transformed from a two-dimensional to three-dimensional imaging device. Even five-dimensional (5D) devices have been used for package inspection, but this 5D X The fluoroscopy system is very expensive and rarely has practical applications in industry. 3. Slice analysis Slice analysis is the process of obtaining the cross-sectional structure of a PCB through a series of means and steps such as sampling, inlaying, slicing, polishing, etching, and observation. Through the slice analysis, a wealth of information reflecting the microstructure of the PCB (through holes, plating, etc.) can be obtained, which provides a good basis for the next step of quality improvement. However, this method is destructive. Once sliced, the sample is inevitably destroyed. At the same time, the method requires high sample preparation, and the sample preparation takes a long time, which requires a well-trained technician to complete. A detailed slicing process is required, which can be referred to the IPC standard IPC-TM-650 2.1.1 and IPC-MS-810. 4. Scanning acoustic microscope Currently used for electronic packaging or assembly analysis, the main mode is the C-mode ultrasonic scanning acoustic microscope, which uses the amplitude and phase and polarity changes generated by high-frequency ultrasonic reflection on the discontinuous interface of the material to image. The Z axis scans the information of the X-Y plane. Therefore, scanning acoustic microscopy can be used to detect components, materials, and various defects inside the PCB and PCBA, including cracks, delamination, inclusions, and voids. If the frequency width of the scanning acoustics is sufficient, the internal defects of the solder joints can also be directly detected. Typical scanning acoustic images represent the presence of defects in a red warning color. Due to the large number of plastic packaged components used in the SMT process, a large amount of moisture reflow sensitive problems occur during the conversion from lead to lead-free processes. That is, the hygroscopic plastic sealing device will cause internal or substrate delamination when reflowing at a higher lead-free process temperature, and the ordinary PCB will often explode at the high temperature of the lead-free process. At this point, scanning acoustic microscopy highlights its unique advantages in non-destructive testing of multilayer high-density PCBs. The general obvious explosion plate can be detected only by visual inspection. 5. Microscopic infrared analysis Micro-infrared analysis is an analytical method that combines infrared spectroscopy with a microscope. It uses different materials (mainly organic matter) to absorb different infrared spectra, analyzes the compound composition of the material, and combines the microscope to make visible light and infrared light The light path, as long as it is visible in the field of view, can be found to analyze trace amounts of organic pollutants. If there is no microscope combination, usually the infrared spectrum can only analyze samples with a larger sample volume. In many cases in electronic processes, trace contamination can lead to poor solderability of PCB pads or lead pins. It is conceivable that it is difficult to solve the process problem without the infrared spectrum of the microscope. The main purpose of microscopic infrared analysis is to analyze the organic contaminants on the surface of the soldered surface or solder joints and analyze the causes of poor corrosion or solderability. 6. Scanning electron microscopy Scanning Electron Microscopy (SEM) is one of the most useful large-scale electron microscopy imaging systems for failure analysis. Its working principle is to use the electron beam emitted by the cathode to accelerate through the anode. After focusing by the magnetic lens, a bundle of several tens of diameters is formed. The electron beam current of several thousand angstroms (A), under the deflection of the scanning coil, the electron beam is subjected to a point-by-point scanning motion on the surface of the sample in a time and space sequence. This high-energy electron beam bombards the surface of the sample and excites A variety of information, through the collection and amplification, can get a variety of corresponding graphics from the display. The excited secondary electrons are generated in the range of 5-10 nm on the surface of the sample. Therefore, the secondary electrons can better reflect the surface morphology of the sample, so it is most often used as a morphology observation; and the excited backscattered electrons are generated on the surface of the sample. In the range of 100-1000 nm, different characteristics of backscattered electrons are emitted with the atomic number of the substance, so the backscattered electron image has the ability of discriminating the morphology and atomic number, and therefore, the backscattered electron image can reflect the chemical element. Distribution of ingredients. The functions of current scanning electron microscopes are already very powerful, and any fine structure or surface features can be amplified to hundreds of thousands of times for observation and analysis. In the failure analysis of PCB or solder joints, SEM is mainly used for the analysis of failure mechanism, specifically to observe the surface structure of the pad surface, the metallographic structure of the solder joint, the measurement of intermetallic compounds, and the solderability coating. Analysis and do tin whisker analysis and measurement. Unlike optical microscopes, SEMs are electronic images, so only black and white, and SEM samples require electrical conduction. Non-conductors and some semiconductors need to be sprayed with gold or carbon, otherwise the charge will accumulate on the surface of the sample. Observation of the sample. In addition, the depth of field of the SEM image is much larger than that of the optical microscope. It is an important analytical method for irregular samples such as metallographic structure, micro-fracture and tin whiskers. 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