FPC common problems and detection methods

FPC (Flexible Printed Circuit), that is, flexible circuit board, flexible PCB. Compared with rigid PCB, it has many advantages, such as: high wiring density, high assembly density, small size, light weight, thin thickness, good bending, can increase the wiring layer, increase design flexibility, and can set circuit and electromagnetic shielding. The layer can be installed with a metal core layer to meet the functions and requirements of special thermal insulation, and is easy to install and highly reliable.


However, FPC also has many problems in the production process. For example, the end number caused by the cutting tolerance problem is insufficient, the cutting machine and the material problem are indented, because of the width problem caused by the slitting of the material, the crease and the warp are caused by the problem of the packaging material and the tube axis. Board, oxidation problems caused by improper storage environment, and so on. Once it appears, it is possible that the entire FPC cannot be used. Therefore, *** thinks that it must be tested.


The existing FPC defect detection methods are mostly derived from PCB detection algorithms, but due to their unique limitations, FPC defect accuracy requirements are higher, the detection template size is larger, the sample image is easily deformed, and the circuit wiring inside the FPC is highly accurate. It is easy to cause line adhesion, crossover and short circuit, and the surface is easy to reflect. The ordinary lens can hardly extract the internal and external lines of the circuit board at the same time, which increases the difficulty of detection. Therefore, the defect detection method of the PCB cannot be directly used for the FPC.


At present, many companies conduct FPC defect detection by means of manual visual inspection. This method is costly and inefficient, and there is no relatively standard quality inspection standard, which is prone to missed detection and false detection. There are also FPC special testing equipment, but due to equipment price, technical support, after-sales service and other limitations, it is difficult to adapt to the low-cost, high-volume production needs of modern technology.


In view of the defects of FPC, China Institute of Metrology divides it into two categories: global defect and local defect. The eight-connected domain area method is combined with histogram matching to capture the global defect of the image. Based on this, the projection matching and correlation coefficient method are used to identify the image. Local defects in . This method is faster and more accurate than the traditional detection algorithm, but the classification of related defect categories is not detailed enough.