As the carrier of various components and the hub of circuit signal transmission, PCB has become an important and crucial part of electronic information products, and its quality and reliability level determine the quality and reliability of the entire equipment. However, due to cost and technical reasons, PCBs have encountered a large number of failure issues in production and application processes.


For this type of failure problem, we need to use some commonly used failure analysis techniques to ensure the quality and reliability level of PCB during manufacturing. This article summarizes nine techniques used for PCB failure analysis, including appearance inspection, X-ray fluoroscopy inspection, metallographic section analysis, scanning acoustic microscope, micro infrared analysis, scanning electron microscopy analysis, X-ray energy spectrum analysis Photoelectron spectroscopy analysis and thermal analysis.


1. Appearance inspection


Appearance inspection is the visual inspection or use of some simple instruments, such as a stereomicroscope, metallographic microscope, or even a magnifying glass, to inspect the appearance of a PCB, find the failure location and related physical evidence, and the main function is to locate the failure and preliminarily determine the failure mode of the PCB. Appearance inspection mainly checks for PCB contamination, corrosion, location of bursting plates, circuit wiring, regularity of failure, whether it is batch or individual, whether it is always concentrated in a certain area, and so on. In addition, many PCB failures are only discovered after assembly into PCBA. It is also necessary to carefully examine the characteristics of the failure area whether it is caused by the influence of the assembly process and the materials used in the process.


2. X-ray fluoroscopy examination


For certain areas that cannot be visually inspected, as well as the internal defects of PCB through-holes and other internal defects, X-ray fluoroscopy systems can only be used for inspection. The X-ray fluoroscopy system utilizes different principles of moisture absorption or transmittance of X-rays based on different material thicknesses or densities. This technology is more commonly used to check the internal defects of PCBA solder joints, through-hole internal defects, and the positioning of defective solder joints in high-density packaged BGA or CSP devices. The current industrial X-ray fluoroscopy equipment can achieve a resolution of less than one micrometer and is transitioning from two-dimensional to three-dimensional imaging devices. There are even five dimensional (5D) devices used for packaging inspection. However, this 5D X-ray fluoroscopy system is very valuable and rarely has practical applications in the industry.


3. Metallographic section analysis


Metallographic section analysis is the process of obtaining the cross-sectional structure of a PCB through a series of methods and steps such as sampling, embedding, slicing, polishing, corrosion, and observation. Through slice analysis, rich information on the microstructure reflecting the quality of PCBs (through holes, coatings, etc.) can be obtained, providing a good basis for the next step of quality improvement. But this method is destructive, and once sliced, the sample will inevitably be destroyed; At the same time, this method requires high sample preparation requirements and a longer sample preparation time, requiring well-trained technical personnel to complete. The detailed slicing operation process can be carried out according to the IPC standards IPC-TM-650 2.1.1 and IPC-MS-810.


4. Scanning acoustic microscope


Currently, C-mode ultrasound is mainly used for electronic packaging or assembly analysis