AOI testing equipment, also known as AOI optical automatic testing equipment, has become an important testing tool and process quality control tool to ensure product quality in the electronic manufacturing industry. Therefore, how to select and use AOI optical automatic testing equipment suitable for their own requirements from a large number of AOI brands has become a problem of great concern to the majority of electronic manufacturing workers.

Principle of AOI detection equipment

During automatic detection, the AOI detection equipment automatically scans PCBA products through the high-definition CCD camera, collects images, compares the tested detection points with the qualified parameters in the database, checks the defects on the target products through image processing, and displays / marks the defects through the display or automatic signs for repair by maintenance personnel and SMT engineering personnel to improve the process.

The general flow of AOI detection equipment is the same, mostly through the graphic recognition method. The standard digital image stored in the AOI system is compared with the actual detected image to obtain the detection result.

For example, when a solder joint is detected, a standard digital image is established according to a perfect solder joint and compared with the measured image. Whether the detection result passes or fails depends on the standard image, resolution and the detection program used. Various algorithms will be used in graphic recognition, such as the proportion of black to white, color, composition, average, sum, difference, plane, corner, etc.

The light of AOI irradiates two types of equipment: white light and color light. White light uses 256 levels of gray, and color uses red light, green light and blue light. The light irradiates the surface of solder / components, and then the light is reflected into the lens to produce a three-dimensional display of two-dimensional images to reflect the height and color difference of solder / components. People see and recognize objects by the amount of light reflected back. Most of the reflected amount is bright, while the less reflected amount is dark. The principle of AOI is the same as that of human judgment.

AOI has single lens and multi lens in terms of lens number, which is only an option for the implementation of the technical scheme. It is difficult to say that the method must be good, because a single lens can also get a good detection image through different angles of multiple light sources. Especially for the rough surface of lead-free welding, which will produce solder joints with different shapes, easy to form bubbles, and easy to have one end of the part cocked, the new AOI equipment has also been updated with adaptive hardware and algorithm.