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Flexible printed circuit boards are more classification methods.According to FPC layer can be divided into: single-sided,double-sided,multilayer and Rigid-Flex PCB. Flexible printed circuit boards(FPCs) market share continues to rise as electronic products tend to miniaturization and lightness. But Flexible printed circuit boards(FPCs) frequently occur breaking, short circuit,line width incorrect defects in processing, feeding, placement and other production processes.This article mainly analyzes the flexible printed circuit boards defect detection method.

Flexible circuit boards(FPCs) have many advantages: good reliability,strong heat dissipation,easy installation and low comprehensive cost, it’s convenient for the high integration and high performance of electronic products.Different production process make it have many unique features.

• ) High density assembly,reducing the connection between different parts.
• ) Light weight,thin thickness can effectively reduce the weight of product,easy to carry.
• ) Can be folded and any bending.

The status of defect detection technology for Flexible printed circuit boards(FPCs)

The existing Flexible printed circuit boards(FPCs) defect detection algorithm is mostly derived from the Printed circuit boards(PCBs),but it limits by its own unique feature,Flexible printed circuit board(FPC) defect precision is higher,the test sample dimension is larger,the test sample is easy to deform,making printed circuit boards（PCB) defect detection algorithm can not directly apply in n flexible printed circuit board defect detection,need develop appropriate detection algorithm according the actual characteristics of flexible circuit boards(FPCs).

In order to solve the problem that traditional template matching algorithm is slow and accuracy is low, the flexible printed circuit board(FPCs) line defect be divided into two types: global defect and local defect,use eight-connected domain area method and the histogram matching method to capture the global defects of the image,on basis of this,use projector matching and correlation coefficient method to recognize the local defects.This method is faster and more accurate than the traditional detection algorithm,but relevant defect classification is not enough.

Analysis of defect detection method for flexible printed circuit board(FPCs)

Aiming the problem of template matching in the global scope,flexible printed circuit board(FPCs) defect detection is implemented considering the local range template matching method.Considering the contour-based template matching method,the template should have significant contour characteristics.Although the conventional lines on the flexible printed circuit boards are regular,but these is no significant shape feature,moreover,the conventional lines are distributed in the whole image, and the template matching time is too slow,it’s unfavorable for line detection.

Shaped lines are irregular shape on the flexible printed circuit board(FPCs),generally including LED lights,S-shaped round.Due to the shape of the peripheral,the layout is generally related to the style of Flexible printed circuit boards. For this type of lines,consider the template matching method to implement test: First through template matching method of steer the various contour lines on the whole Flexible printed circuit boards position,access to contour lines,and then based on morphological theory for defect detection.

The detection process of the special shape line is below:

1. Load the registration template related data information,including the registration template area,registration template contour information.
2. Using the area information carried by registration template,locate the template search space,and search the template instance in the search image based on the normalized mutual correlation coefficient metric principle.
3. Cut the contour area. The size of the profiled area is obtained by finding the smallest circumscribed rectangle of the shape template instance,since the shape template is a rectangular region,so the area obtained by the minimum circumscribed rectangle is the matching alien region. Any template matching can not make the two images perfectly aligned in space, there is a permissible range of matching. Flexible printed circuit boards(FPCs) local area of the deformation can be ignored,in the limited space on the shape of the template matching due to narrowing spatial range,shape template matching accuracy,the overall matching error of about 1/5 line width(3 pixels) range,is in allowable range.
4. Considering the accuracy error of shape matching,before the standard template image and the profiled area image are directly measured, the small-size structural elements are used to etch the alien-shaped area to remove the boundary difference effect.when the image is defective,the corrosion operation at this size can not completely corrode the defective line, so it does not affect the final judgment result.
5. The template image and the contour area of the regional difference set operation, access to the difference between the two areas.When there is no defect,the difference is 0.When there is a defect,the area difference set returns a binary image that is not zero.
6. The difference image is connected to the domain label,split the different defect block.
7. The area of each connected domain is calculated,and the center of the geometric dimension of the largest defective block is used as the center of the profiled area to output the defect inforation.

The FPC defect detection method is studied from the global and local scope,and the experimental results are drawn:

• ) Due to FPC imaging deformation,based on the global scope of the template matching line dislocation,can not correctly locate the image on the defect information.   

• ) Based on the local scope of the template matching,first cut out the FPC board relative to the conventional line with significant shape characteristics of the line area,as a template source. In the search image corresponding to the template area near the instance detection,compression search space,and then based on morphological theory to detect line defect information.

In short, the circuit board as the most basic part of the electronic circuit, a great impact on the quality of the entire electronic products. Therefore, how to achieve accurate detection of circuit board defects is an important part of product quality assurance, and most domestic enterprises generally rely on artificial visual inspection FPC defect detection, high cost, low efficiency, and because there is no relatively standardized quality standards, the staff Subjective awareness or visual fatigue and other reasons prone to missed and false detection; some enterprises to introduce foreign excellent testing equipment, by the equipment prices, technical support, after-sales service and other limitations, it is difficult to adapt to modern technology, low-cost, high-volume production needs. Therefore, the development of a fast and efficient FPC defect automatic detection system to meet the domestic market demand is imminent.

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