The AOI detector can be used in multiple locations on the production line, and it can detect special defects at various locations.
However, the AOI detector should be placed in a position where the most defects can be identified and corrected as early as possible.
JOYSMT describes in detail the role of the AOI detector in three inspection positions.
1. AOI inspection after solder paste printing When 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: (1) insufficient solder on the pad; (2) too much solder on the pad; (3) Poor adhesion of solder to the pad; (4) Solder bridge between pads.
On ICT, the probability of defects in these cases is proportional to the severity of the situation. Slightly less tin rarely causes defects, while in severe cases, if it is completely tin-free, it is easy to cause defects in ICT. Insufficient solder may be an important cause of missing components or open solder joints. Still, deciding where to place the AOI detector requires recognizing that component loss may be caused by other causes, and these reasons must be placed in the inspection plan. This location check supports process tracking and characterization directly. The quantitative process control data at this stage includes print offset and solder volume information, which will produce qualitative information on the printed solder.
2. AOI detection before reflow soldering The inspection is done after the component is placed on the solder paste in the board and before the PCB is fed into the reflow oven. This is where the inspection machine is typically placed. Because most of the defects from solder paste printing and machine placement can be found here. Quantitative process control information generated at this location provides information on the calibration of high speed and closely spaced component placement equipment. This information can be used to modify component placement or indicate that the placement machine requires calibration.
3. AOI inspection after reflow soldering Checking at the last step of the SMT process, which is currently the most popular method for AOI detectors. Because this position can find all assembly errors. Post-reflow inspection provides a high degree of safety as it identifies errors caused by solder paste printing, component placement and reflow processes.