AOI Guidelines In PCB Manufacturing

AOI inspection is an inspection that inspects and tests circuit boards for any possible defects. AOI test pcb uses automated machines to test PCBs. This PCB inspection technique checks for errors such as component placement defects.

The PCB board’s surface is scanned during the AOI examination. The HD color cameras on the AOI machine scan the surface at high magnification, clearly displaying on a larger monitor the intricacies of each PCB piece and each component within it. The camera uses a light source, such as fluorescent or LED lights, PCBs, UV or infrared light, to take pictures of the PCB surface.
After that, the image is compared to the pre-programmed information and supplied into the AOI processing system’s memory. The process is instantly stopped if the difference or Normalized Cross Correlation (NCC) is determined to be greater than the tolerance level. The difference between captured and pre-programmed (template) photos decreases with increasing NCC. Several algorithms running on the AOI machine dependent on pixel counts and NCC values determine the ultimate decision to deem the board to be defective and thus stop the process.

The AOI machine operator can manually halt the process as needed by visually inspecting the images the AOI machine has captured on the screen. By separating the object image from the backdrop, the “blobs or pixels” of the pixels-based image are integrated or grouped, and errors are then found.
To check for component placement, location, and condition (i.e., flaws unrelated to soldering), the AOI can be performed prior to reflow. The post-reflow AOI finds flaws that may have resulted from the reflow oven’s thermal dynamics in soldering joints, components, and the PCB board itself.
Smallest components like 01005, 0201, and 0402 packages as well as IC packages like QFP, QFN, CSP, and BGA and PoP can be scanned by the AOI machine, but only for surface inspection, not for underneath the package examination. It should be noted that AOI cannot inspect components that are located under the body or packaging of an IC.
AXI is required for this. As X-Rays can see through the body, the component identification underneath the IC package can be done using greyscale pictures.