What Does AOI Testing Technology Do

In the PCB copying process, especially when copying some high-precision circuit boards, testing is an indispensable step. Only the test can assess whether these PCB copying boards are qualified. The most commonly used testing equipment in circuit board copying is flying probe testing machine and test frame testing. In fact, there is another electronic tester AOI. AOI is a new type of testing technology that has only emerged in recent years, but its development is relatively rapid. At present, many manufacturers have launched AOI testing equipment. When automatic detection, the machine automatically scans the PCB through the camera and collects the images. The tested solder joints are compared with the qualified parameters in the database. After image processing, the defects on the PCB copy board are checked, and the defects are displayed on the display or automatic marked for technicians to fix.

1. Implementation goals: There are two main types of goals for implementing AOI:

(1) End quality. Monitor the final state of the product as it leaves the production line. When production issues are very clear, product mix is high, and quantity and speed are key factors, this goal is preferred. AOI is usually placed at the very end of the production line. In this position, the device can generate a wide range of process control information.

(2) Process tracking. Use inspection equipment to monitor the production process. Typically includes detailed defect classification and component placement offset information. When product reliability is important, low-mix and high-volume manufacturing, and component supply is stable, manufacturers prioritize this goal. This often requires placing inspection equipment in several locations on the production line to monitor specific production conditions in real time and provide the necessary basis for the adjustment of production processes.

Although AOI can be used in multiple locations on the production line, each location can detect special defects, but AOI inspection equipment should be placed in a location that can identify and correct the most defects as soon as possible.

2. There are three main inspection locations:

(1) After solder paste printing. If the solder paste printing process meets the requirements, the number of defects found by ICT can be greatly reduced. Typical printing defects include the following: A. Insufficient solder on the pad. B. Too much solder on the pad. C. The solder is poorly aligned with the pad. D. Solder bridge between pads.

In ICT, the probability of defects relative to these situations is directly proportional to the severity of the situation. Minor little tin rarely causes defects. While severe cases, such as no tin at all, almost always cause defects in ICT. Insufficient solder may be a cause of missing components or open solder joints. Nonetheless, deciding where to place the AOI requires recognizing that component loss may have occurred for other reasons, which must be included in the inspection plan. The inspection of this location most directly supports process tracking and characterization. The quantitative process control data at this stage includes printing offset and solder volume information, and qualitative information about printed solder will also be generated.

(2) Before reflow soldering. The inspection is done after the components are placed in the solder paste on the board and before the PCB circuit board is sent to the reflow furnace. This is a typical location for inspection machines because most defects from solder paste printing and machine placement can be found here. The quantitative process control information generated at this location provides information for the calibration of high-speed chip mounters and closely spaced component placement equipment. This information can be used to modify component placement or indicate that the placement machine needs calibration. The inspection at this location meets the goal of process tracking.

(3) After reflow soldering. Check at the last step of the SMT process, which is currently the most popular choice for AOI, because all assembly errors can be found at this location. Post-reflow inspection provides a high degree of safety because it identifies errors caused by solder paste printing, component placement, and reflow processes.