What is AOI detection? Functions of automatic product appearance inspection equipment

Date：2022-10-17 17:08:23Views：1116

Automated Optical Inspection (AOI) is a high-speed and high-precision optical image detection system. Using machine vision as the detection standard technology, it can improve the shortcomings of the traditional manual use of optical instruments for detection. The application level includes the research and development of high-tech industries, manufacturing quality management, as well as national defense, people's livelihood, medical care, environmental protection, power and other fields.

Taking SMT detection as an example, during automatic detection, the machine automatically scans the PCB through the camera, collects images, compares the tested solder joints with the qualified parameters in the database, checks the defects on the PCB through image processing, and displays/marks the defects through the display or automatic marks for repair by maintenance personnel.

Functions of AOI visual inspection equipment:

(1) The light source of AOI is composed of red, green and blue LED lights. The three primary color principle of color is used to combine different colors. Combining the specular reflection, diffuse reflection and oblique reflection in the optical principle, the patch elements on the PCB and the welding status are displayed in the form of images.

(2) The weight imaging data difference analysis system is to grid an image, analyze the location coordinates of each pixel color distribution, the (color) transition relationship between imaging grids and other imaging details, list several functional formulas, and then extract data from several similar pictures of the same area size, analyze and calculate, restore the calculation results according to the weight relationship set by the software and the color and coordinates of the original image pixels, A virtual digital image with weight value is formed. This image is called "weight image". Its main digital information includes the graphic outline of the image, the distribution of colors, the weight relationship allowed to change, etc., for later analysis and processing.

(3) Similarity principle. The contour of the object is formed by the light dark relationship of the image, and the similarity between the contour and the standard contour is compared. This method is effective in detecting the missing and missing of components.

(4) Color extraction. Any color can be mixed with red, green and blue in a certain proportion. Red, green and blue form a three-dimensional color cube. Color extraction is to cut a required small color cube from the color cube, that is, corresponding to the range of colors we need to select, and then calculate the proportion of the detected image that meets the color cube in the total number of image colors to check whether it meets the required setting range. Under the condition of red, green and blue light, this method is most suitable for detecting solders such as resistors and capacitors.

(5) Image comparison. During the test, the equipment collects the image on the tested circuit board through the CCD camera system, inputs the image into the computer after digital processing, and compares it with the standard image (the comparison items include the size, angle, offset, brightness, color, and position of the component). The image whose comparison result exceeds the rated error threshold is output through the display, and displays its specific position on the PCB.

(6) Binary principle. The target image is converted into a gray image in a certain way, and then a certain brightness threshold is selected for image processing. The image below the threshold is directly converted to black, and the image above the threshold is directly converted to white. The characters, IC short circuits, etc. are directly separated from the original image.

AOI four detection positions:

(1) After solder paste printing, mainly check the solder paste printing;

(2) After the chip component is placed, check whether the chip is correct, so that errors can be found earlier and costs can be reduced;

(3) After the chip is placed, the detection system can check the missing, offset and skewed chips on the PCB and the error of chip polarity;

(4) After reflow soldering, at the end of the production line. The detection system can detect the missing, offset, skew and polarity defects of components.

Among the four AOI detection positions, the detection after solder paste printing, (chip) device placement and component placement is aimed at preventing problems. Detection at these positions can prevent the occurrence of defects; Detection after reflow soldering is aimed at finding problems. The problem prevention AOI shall be placed in front of the furnace, and the problem AOI found shall be placed behind the furnace.

With the increasingly ultra-thin, high-density and fine spacing of PCBs, the line width and spacing of components on PCB have reached the micron level, and manual detection is far from meeting the detection requirements of such high precision. AOI detection technology is more stable, accurate and repeatable, which makes the missed detection rate and false detection rate of any PCB process defects tend to zero. Our company has a team of professional engineers and industry elites, and has built three standardized laboratories with an area of more than 1800 square meters, which can undertake a variety of test projects such as electronic component test verification, IC authenticity identification, product design material selection, failure analysis, functional testing, factory incoming material inspection and tape weaving.