PCB as a carrier of various components and circuit signal transmission hub has become the most important and critical part of electronic information products. The quality of its quality and reliability determines the quality and reliability of the entire equipment.
With the miniaturization of electronic information products and the environmental protection requirements of lead-free and halogen-free, PCBs have also developed toward high density, high Tg, and environmental protection. However, due to cost and technical reasons, PCBs have suffered a large number of failures during production and application, and this has led to many quality disputes. In order to clarify the cause of the failure in order to find a solution to the problem and to clarify the responsibility, a failure analysis must be performed on the failed case.
Failure Analysis Basic Procedure
To obtain the exact cause or mechanism of a PCB failure or defect, the basic principles and analysis flow must be followed, otherwise valuable invalidation information may be missed, causing the analysis to continue or possibly obtaining erroneous conclusions. The general basic process is, first of all, based on the failure phenomenon, through the information collection, functional testing, electrical performance testing and simple visual inspection, determine the failure location and failure mode, that is, the failure location or fault location.
For a simple PCB or PCBA, the failure location can be easily determined. However, for a more complex BGA or MCM packaged device or substrate, the defect is not easily observed by the microscope. It is difficult to determine for a moment, and this time needs to be determined by other means.
Then we need to analyze the failure mechanism, that is, use various physical and chemical means to analyze the mechanism that leads to PCB failure or defects, such as welding, contamination, mechanical damage, moisture stress, medium corrosion, fatigue damage, CAF or ion migration, Stress overload and so on.
Then, the failure analysis is based on failure mechanism and process analysis to find the cause of the failure mechanism. If necessary, test verification is carried out. Generally, the test should be performed as far as possible, and the exact cause of induction failure can be found through the test verification.
This provides a basis for targeted improvement of the next step. Finally, according to the experimental data obtained from the analysis process, facts and conclusions, the failure analysis report was prepared. The report requires clear facts, strict logical reasoning, and strong rationality.
During the analysis process, pay attention to the basic principles that the analysis method should be used from simple to complex, from outside to inside, never to destroy samples, and then use destruction. Only in this way can we avoid losing key information and avoid introducing new artificial failure mechanisms.
Just like a traffic accident, if a party to the accident destroys or flees the scene, it is difficult for a clever policeman to make an accurate determination of liability. At this time, the traffic regulations generally require that the person fleeing the scene or destroying the scene bear full responsibility.
The same is true for the failure analysis of PCB or PCBA. If soldering iron is used to repair the failed solder joints or if large shears are used to sharply cut the PCB, reanalysis will be impossible. The failure site has been destroyed. Especially in the case of a small number of failure samples, the true failure cause cannot be obtained once the failure site environment is destroyed or damaged.
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