PCB failure detection and application of electronic component failure analysis technology

Date：2022-02-25 13:38:39Views：922

As we all know, product failure will cause serious economic losses and quality impact. However, PCB failure modes are diverse and the root causes of failure are also different. The main material of PCB is the composite of glass fiber and epoxy resin, which is divided into single panel, double-sided board and multilayer board. Therefore, how to quickly locate the root cause of PCB failure and optimize and improve the performance of products has become the focus of PCB industry.

Failure mechanism is a physical or chemical process that leads to the failure of parts, components and materials. The inducing factors of this process are internal and external. When studying the failure mechanism, we usually start with the external inducing factors and failure manifestations, and then study the more hidden internal factors. For simple PCB or PCBA, the failure position is easy to determine. However, for more complex BGA or MCM packaged devices or substrates, it is not easy to determine at this time. At this time, it needs to be determined by other means.

1. Optical microscope

Optical microscope is mainly used for the appearance inspection of PCB, looking for the failed parts and relevant physical evidence, and preliminarily judging the failure mode of PCB. The appearance inspection mainly checks the pollution and corrosion of PCB, the position of board explosion, circuit wiring and failure area, etc.

2. X-ray (X-ray)

X-ray fluoroscopy system can only be used to inspect some parts that cannot be detected through appearance inspection, as well as the through hole interior of PCB and other internal defects. This technology is more used to check the internal defects of PCBA solder joints, internal defects of through holes and the positioning of defective solder joints of high-density packaged BGA or CSP devices.

3. Slice analysis

Slice analysis is the process of obtaining the cross-sectional structure of PCB through a series of means and steps such as sampling, mosaic, slicing, polishing, corrosion and observation. Slice analysis can get rich information about the microstructure reflecting the quality of PCB (through hole, coating, etc.), which provides a good basis for the next quality improvement.

4. Scanning acoustic microscope

At present, the C-mode ultrasonic scanning acoustic microscope is mainly used for electronic packaging or assembly analysis. It uses the amplitude, phase and polarity changes generated by the reflection of high-frequency ultrasound on the discontinuous interface of materials to image. Its scanning method is to scan the information of X-Y plane along the Z axis. Scanning acoustic microscope can be used to detect various defects in components, materials and PCB and PCBA, including cracks, delamination, inclusions and cavities. If the frequency width of scanning acoustics is enough, the internal defects of solder joints can also be detected directly.

5. Micro infrared analysis

At present, the C-mode ultrasonic scanning acoustic microscope is mainly used for electronic packaging or assembly analysis. It uses the amplitude, phase and polarity changes generated by the reflection of high-frequency ultrasound on the discontinuous interface of materials to image. Its scanning method is to scan the information of X-Y plane along the Z axis.

Micro infrared analysis is an analysis method combining infrared spectrum with microscope. It uses the principle of different absorption of infrared spectrum by different materials (mainly organic substances) to analyze the compound composition of materials. Combined with microscope, visible light and infrared light can be in the same light path. As long as it is in the visible field of view, it can find trace organic pollutants to be analyzed. Micro infrared analysis is an analysis method that combines infrared spectrum with microscope. Its main purpose is to analyze the organic pollutants on the surface of the welded surface or solder joint, and analyze the causes of corrosion or poor weldability.

6. Scanning electron microscopy (SEM)

Scanning electron microscope (SEM) is the most useful large-scale electron microscopic imaging system for failure analysis. It is most commonly used for morphology observation. At present, the function of scanning electron microscope is very powerful. Any fine structure or surface feature can be magnified to hundreds of thousands of times for observation and analysis. In the failure analysis of PCB or solder joint, SEM is mainly used to observe the morphology and structure of pad surface, the metallographic structure of solder joint, measure intermetallic compounds, analyze solderable coating, and analyze and measure tin whisker.

7. Differential scanning calorimeter (DSC)

Differential scanning calorimetry (DSC) is a method to measure the relationship between the power difference input to the substance and the reference substance and temperature (or time) under programmed temperature control. DSC is mainly used to measure the curing degree and glass transition temperature of various polymer materials used on PCB in PCB analysis. These two parameters determine the reliability of PCB in the subsequent process.

8. Thermomechanical analyzer (TMA)

Thermomechanical analysis (Thermal Mechanical Analysis) is used to measure the deformation properties of solids, liquids and gels under thermal or mechanical stress under programmed temperature control. TMA is widely used. In the analysis of PCB, it is mainly used for the two key parameters of PCB: measuring its linear expansion coefficient and glass transition temperature. The PCB of the substrate with too large expansion coefficient often leads to the fracture failure of the metallized hole after welding and assembly.

9. Thermogravimetric analyzer (TGA)

Thermogravimetry (TGA) is a method to measure the change of material mass with temperature (or time) under programmed temperature control. In the aspect of PCB analysis, it is mainly used to measure the thermal stability or thermal decomposition temperature of PCB materials. If the thermal decomposition temperature of the substrate is too low, the PCB will burst or delamination failure after high temperature in the welding process.

As the carrier of various components and the hub of circuit signal transmission, PCB has become the most important and key part of electronic information products, which is widely used in all walks of life.