As an important part of modern electronic equipment, PCB is an information carrier integrating various electronic components, which is widely used in the electronic field, and its quality can directly affect the performance of products.
With the development of electronic technology and electronic manufacturing industry, due to the small size and high installation density of patch components, the integration of PCB board is required to be further improved.
01 Conventional inspection of production lines
In the early days of industrial production, quality inspection of products was mainly done manually, and it was the last part of production.
But with the development of manufacturing scale and automation, large-scale product stacking, quality inspectors are difficult to keep up with the speed of detection, equipped with multiple quality inspectors, and can not be configured with the number of mobile work orders. Coupled with the monotony and repetition of quality inspection tasks, resulting in uneven levels of testing, it is difficult to ensure customer satisfaction.
Appearance inspection is a very important part of the quality inspection process, the accuracy, efficiency, speed and other aspects of the inspection have high requirements, PCB internal process is complex, in addition to the core board structure lamination, drilling, wiring, but also need to consider buried components, surface finishing, cleaning and etching. Due to the high degree of dependence on the accuracy of production equipment and material performance, generally in the design and production process, it is easy to have the following types of problems.
- PCB process edge design is unreasonable, resulting in the equipment not be placed.
- CB positioning hole problem, leading to the equipment can not be accurately and firmly positioned.
- Screw hole metallization, resulting in blocking holes after over wave soldering.
- PCB pad problem, soldering with false solder, shift, standing monument, or solder point less tin.
- Mark point design problems, resulting in machine identification difficulties.
- Bit number or polarity mark missing, bit number reversed, character too big or too small, etc.
- The distance between test points and components is not placed in a standardized way, and the serviceability is poor.
The traditional manual detection method is easy to miss detection, slow detection speed, long detection time and high cost, which has gradually failed to meet the production needs. In order to ensure the performance of electronic products, PCB defect detection technology has become a very key technology in the electronic industry.
02 AI machine vision inspection is the general trend.
With the increasingly ultra-thin, high-density and fine spacing of PCB, the line width and spacing of components on PCB circuit board have reached micron level, and manual inspection is far from meeting the requirements of such high-precision inspection.
Machine vision inspection technology is based on image processing algorithm, which is realized by digital image processing and pattern recognition. Compared with traditional manual inspection technology, it improves the efficiency and accuracy of defect detection.
Machine vision systems generally use CCD or CMOS industrial cameras to capture inspection images and convert them into digital signals, and then process the digital signals through computer software and hardware technology to obtain the required target image feature values, and thus achieve a variety of functions such as part identification or defect detection.
Identification and classification detection
The shape, size and inner hole of PCB are visually detected and matched with the black-and-white feature map of the product loaded by the system to identify the number of the board.
Borehole coding detection
Drilling marks are decoded according to the coding rules.
Pad appearance detection
In the PCB production process, there will be the phenomenon that the pad is covered with oil after the development line. Timely detection and discovery of problems at this station can reduce a series of subsequent processes and save costs.
Character reading detection
Check whether the character code form of PCB meets the standard, whether it is clear and free from defects, whether the lines are smooth and free from bumps, and whether there are defects such as line recombination, ghost, pockmarks, deformation, color difference, offset and misprint.
Machine vision inspection technology can realize the inspection of PCB, BGA, pins and patches, as well as the integrity inspection of solder joints, missing components and wrong directions.
For example, whether there are stains, sundries, pits and tin residue on the surface of PCB; Whether the surface characters and symbols are clear; Whether the tin on the pad is uniform, and so on.
03 Application of machine vision technology in PCB inspection
PCB inspection schemes are mainly divided into 2D and 3D.
2D can detect many kinds of defects such as short circuit, empty welding, tin hole and less tin, and the hardware types and system layout schemes are different for different defects.
The commonly used equipment in 3D, such as laser line scanning /PMP, can not only realize contour scanning, but also realize the detection of tiny QFN and LGA components. Their application scenarios and defect types are different.
1. 2D detection
Take the testing case of circuit board components as an example:
Product testing requirements
1. Check whether the capacitor is missing or not, and whether the positive and negative electrodes are reversed.
2. Check whether the connector is missing or not, and whether it is installed backwards or forwards.
According to the different printed patterns on the two ends of the capacitor, the positive and negative differences, that is, the polarity of the capacitor, are distinguished by machine vision technology.
2. 3D detection
Aiming at the 3D detection scheme in PCB field, the industry mainly adopts laser line scanning/sine stripe PMP and other schemes to realize it. Laser line scanning scheme usually uses laser profilometer combined with conveying mechanism (similar to 2D linear array inspection system) to realize PCB surface modeling and automatic inspection.