PCBA solder paste placement accuracy directly affects the soldering effect of components, especially for small-pitch components such as 0201 chips and BGA packages, so accurate inspection methods are crucial. The first commonly used method is visual inspection, which is suitable for preliminary screening of large-pitch components. Inspectors use magnifying glasses or stereoscopes to observe the position, shape and size of the solder paste on the pad. The qualified solder paste should be accurately aligned with the pad, without offset, overflow or missing. The width and thickness of the solder paste should be consistent with the design requirements—too thick may lead to bridging, while too thin may cause insufficient soldering. However, visual inspection has limitations for small-pitch components and is easily affected by human factors, so it is usually used in combination with other methods.

Another efficient and accurate method is automatic optical inspection (AOI). AOI equipment uses high-resolution cameras to capture images of the PCB surface, and compares the collected images with the pre-stored standard images through image processing technology to automatically identify the offset, overflow, missing, and uneven thickness of the solder paste. AOI has the advantages of high inspection speed, high accuracy, and strong repeatability, and can effectively detect small-pitch components and dense solder paste positions that are difficult to identify by visual inspection. It can also generate inspection reports in real time, facilitating quality tracking and analysis. For high-precision PCBA, 3D AOI can be used to detect the three-dimensional shape of the solder paste, including its height and volume, to ensure that the solder paste amount meets the soldering requirements.

In addition, offline inspection methods can be used for key PCBA products. For example, using a solder paste inspection (SPI) machine to accurately measure the volume, area, height and other parameters of the solder paste, and compare them with the set standard values to determine whether the placement accuracy is qualified. SPI can detect subtle defects such as solder paste voids and uneven distribution, which provides a reliable basis for adjusting the solder paste printing process. No matter which inspection method is used, the inspection standards should be formulated according to the PCB design specifications and component requirements, and regular calibration of inspection equipment should be carried out to ensure the accuracy and reliability of the inspection results.