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Flex rigid PCB failure analysis steps

Article source:Editor:何琴 Mobile phone view
Popularity:1097Dated :08-31-2021 04:45【big well Small

As the carrier of various components and the hub of circuit signal transmission, Flex rigid PCB has become the most important and key part of electronic information products and is widely used in various industries. In recent years, due to the increasing number of PCB failure cases, partial failures are extremely harmful. Nowadays, we have higher and higher product quality requirements and stricter control over product reliability. Therefore, the quality and reliability of the PCB determines the quality and reliability of the entire equipment.

Sun&Lynn gives you an analysis, what are the steps of Flex rigid PCB failure analysis.

1. Visual inspection
Cracks on the substrate indicate the presence of stresses such as bending, and overheated or discolored lines are a sign of overcurrent. Cracked solder joints indicate solderability problems or solder contamination. Some solder joints have dark surfaces or too much or too little solder. These characteristics are signs of poor soldering technology, contamination or overheating. Any discoloration is possible. Means overheating. Solder reflows to create porosity, which means high temperature.

2. X-ray
Check for any disconnection/shorting or circuit damage, incompletely filled vias, misaligned circuits or component pads.

3. Electrical measurement
Used to confirm cracked and broken solder joints, leakage caused by contaminants, voltage can be added to measure current, but the voltage should be limited to a reasonable range. Applying some stress during the test may find some intermittent abnormalities.

4. Cross-section analysis
For solder joints and internal defects of multilayer boards, the method of preparing metallographic samples can be used to check.

5.SEM and EDX
Contaminants on the surface of the substrate can be identified by SEM. Contaminants may appear on the surface of the board or under the conformal coating. Sometimes the conformal coating must be removed first without affecting the contaminants, chlorine, fluorine, sulfur, and Bromine is an element of concern, and bromine is a flame retardant component that plays a flame retardant effect in certain materials. EDX can be used to check whether there are contaminants in the solder joints. Sulfur, oxygen, copper, aluminum and zinc are all contaminants that may cause problems in the solder joints. The solder joint cracks caused by contaminants often occur at the interface between the component pins and the solder. At the intermetallic compound.

Method to remove the conformal layer:
1. Dissolve with a solvent. Solvents such as xylene, trichloroethane, methyl acetaldehyde, ketone, and methylene chloride can remove the conformal layer, but do not damage the board or pollutants.

2. Thermal separation, using a controllable low-temperature heating method. This method is best for thick coatings. Heat is directly applied to the coating to separate it from the base material.

3. Grind off, use a spraying device similar to sandblasting to remove those coatings that are impossible to melt away with solvents.

4. Plasma etching, place the board in a vacuum chamber and use low-temperature plasma to remove the coating. This method is very effective for the removal of parylene.


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