The role of automatic optical inspection (AOI) technology in PCBA processing
In PCBA processing, automatic optical inspection is usually set at the last step of the SMT production line, and it is necessary to detect the defects of the product after the completion of the SMT processing process. Improve assembly efficiency and avoid material waste through timely detection and reduction of defects.
AOI is a kind of inspection equipment, also known as AOI optical automatic inspection equipment, has become an important inspection tool and process quality control tool for the electronic manufacturing industry to ensure product quality. The working principle of AOI detection equipment is that in the automatic detection process, the AOI detection equipment automatically scans PCBA products through the high-definition CCD camera, collects images, compares the test point with the qualified parameters in the database, checks the solder joint defects on the target PCBA after image processing, and displays or automatically marks the defects. Improve process parameters for maintenance personnel and SMT technicians.
The AOI system includes multiple light sources, high-speed digital cameras, high-speed linear motors, precision mechanical transmission structures and image processing software. During the test, AOI equipment automatically scans and captures images of PCB, PCB parts or special parts (including the status of printed solder paste, SMD components, solder joint shape and defects, etc.) by camera, compares the qualified parameters through processing and database software, and comprehensively determines whether the components and characteristics are qualified, and then tests the conclusion. Such as missing components, bridging or solder joint quality problems.
AOI works in the same way as the vision systems used in SPI and printing presses in SMT, typically using design rule checking (DRC) and pattern recognition. The DRC method checks the circuit pattern according to some given rules (all wires should end at the solder joint, all leads should be at least 0.127 mm wide, all leads should be at least 0.102 mm apart, etc.). This method can guarantee the correctness of the circuit to be tested algorithmically, and has the characteristics of simple production, simple algorithm logic, fast processing speed, small amount of program editing, and small data space, so it is adopted by many people. But the ability of this method to determine the boundary is poor.
The method of image recognition is to compare the stored digital image with the actual image. Tests are carried out according to the complete printed circuit board or according to the test documents established by the model, or according to the test procedures prepared in the computer shaft aided design. Its accuracy depends on the licensing rate and inspection procedures used, generally the same as the electronic test system, but the amount of data collected is large, and the real-time processing of data is higher. The pattern recognition method uses actual design data to replace established design principles in DRC and has obvious advantages.
AOl has components testing, PCB board testing, welding components testing and other functions. The general procedure of AOI inspection system for parts inspection is to automatically count the printed circuit board of the installed parts and start the inspection; Check the lead side of the printed circuit board to ensure that the lead end is aligned and bent correctly; Check whether there are missing parts, wrong parts, damaged parts, check the type, direction and position of the installed IC and discrete devices, check the quality of the mark printing on the IC device. If AOI finds a defective part, the system sends a signal to the operator, or triggers a handler that automatically removes the defective part. The system analyzes defects, provides the type and frequency of defects to the host machine, and makes the necessary adjustments to the manufacturing process. The efficiency and reliability of AOI inspection depends on the integrity of the software used. AO also has the advantages of being easy to use, easy to adjust, and no need to write algorithms for visual systems.
Our own SMT processingplant can provide SMT processing services for minimum package 0201 components. The SMT plant is equipped with 3 Fuji high-speed SMT lines, 2 DIP plug-in production lines, equipped with AOI optical detector, automatic solder paste printing machine, semi-automatic solder paste printing machine, lead-free wave soldering, lead wave soldering, upper and lower 8 temperature zone reflow welding, PCBA functional test frame, aging, board loading machine, cleaning tools, etc., at the same time, a professional research and development laboratory is set up. Five professional engineers cooperate with customers to perform general functional testing, test point testing, as well as channel, noise, waveform, drop and temperature testing. The company specializes in providing overall PCBA electronic manufacturing services, including upstream electronic component procurement to PCB production and processing, SMT patches, DIP plug-ins, PCBA testing, finished product assembly and other one-stop services.
The company gives full play to its competitive advantages in scale procurement and quality control, and has signed long-term cooperation agreements with many electronic component manufacturers at home and abroad and around the world to ensure the quality and stable supply of raw materials, and transfer the benefits to customers.