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Basic procedure for PCB failure analysis

143 Published by FASTPCBA 6月 19,2019

Basic procedure for PCB failure analysis

As the hub of various components and circuit signal transmission, PCB has become the most important and key part of electronic information products. Its quality and reliability determine the quality and reliability of the whole equipment. With the miniaturization of electronic information products and the environmental requirements of lead-free and halogen-free, PCBs are also developing in the direction of high density and high Tg and environmental protection. However, due to cost and technical reasons, PCBs have experienced a large number of failures in the production and application process, and thus caused many quality disputes. In order to clarify the cause of the failure so that finding a solution to the problem and to clarify the responsibility, a failure analysis must be performed on the failure case that occurred.

PCB failure analysis

To obtain the exact cause or mechanism of PCB failure or defective, you must follow the basic principles and analysis procedures, otherwise valuable failure information may be missed, resulting in the analysis can not continue or may get wrong conclusions. The general basic process is to first determine the failure location and failure mode, that is failure location or fault location, based on failure phenomena, through information collection, functional testing, electrical performance testing, and simple appearance inspection.

For a simple PCB or PCBA, the location of the failure is easy to determine. However, for a more complex BGA or MCM packaged device or substrate, the defect is not easily observed by the microscope, and it is difficult to determine at a short time. This time, other means are needed to help determine. The failure mechanism is then analyzed by using various physical and chemical methods to analyze the mechanism that causes PCB failure or defect generation, such as virtual welding, contamination, mechanical damage, moisture stress, dielectric corrosion, fatigue damage, CAF or ion migration, stress overload and so on.

Then the failure cause analysis, that is, based on the failure mechanism and the process analysis, finding the cause of the failure mechanism, and if necessary, carry out test verification. Generally, the test should be carried out as far as possible, and the cause of the induced failure can be found through the test verification. This provides a targeted basis for the next step of improvement. Finally, according to the test data, facts and conclusions obtained in the analysis process, the failure analysis report is compiled, and the facts of the report are clear, the logical reasoning is strict, the rules are strong, and it is forbidden to imagine.

In the process of analysis, pay attention to the basic principles of using analytical methods from simple to complex, from the outside to the inside, from the destruction of the sample to the use of damage. Only in this way can we avoid losing key information and avoid introducing new artificial failure mechanisms. Just like a traffic accident, if one of the accidents destroys or flees the scene, it is difficult for even the best police to make an accurate responsibility confirmation. At this time, the traffic regulations generally require the party who fled the scene or the party damaged the scene to bear full responsibility. The same is for the failure analysis of PCB or PCBA. If the soldering iron is used to repair the failed solder joints or the large scissors are used to strongly cut the PCB, then the analysis will not be possible, and the failed scene has been destroyed. Especially in the case of a small number of failed samples, once the environment of the failed site is destroyed or damaged, the real cause of failure cannot be obtained.

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