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How AOI works on PCBA Quality Inspection?

Table of Contents

Automated Optical Inspection, shorted as AOI, is a visual inspection technology that uses cameras to scanning PCB with photographic processing system, to automatically compare the photos against the standard reference, and identifying the difference, catagorize as defects on PCB and alert.

The 4 key modules which consist a typical AOI system:

  • High-resolution cameras: scanning PCBs and capturing the photos in high-resolution, passing on to processing system;
  • Lighting: provides sufficient lighting, supports cameras to capturing clear & accurate photos of PCBs.
  • Photographic processing system: Analyze the captured photos and compare against the reference, identify difference which might be defects.
  • Conveyor: transport PCB from operating station to the places under cameras for inspection.

AOI inspection process has 5 core steps:

  1. PCB loading: place PCB on the conveyor and transport to under cameras.
    Photographic capturing: High-resolution cameras scanning and capturing photos of the PCB.
  2. Photographic processing: process the captured photos and turn into certain form.
  3. Comparing and Identifying: comparing the captured photos against the reference, which was inspected, approved and loaded in processing system in advance, identifying the differences.
  4. Pass-on or alert failure: If everyting is correct, then pass-on and release, if any difference is identified and might be defects, alert as potentical failure.
  5. PCB unloading: transport PCB out for unloading, waiting for next step or rework.

Nowdays, AOI is widely applied and very popular to inspect the PCB assembly quality after SMT process, the visible defects are:

πŸ”Ή Components absence
πŸ”Ή Components migalignment
πŸ”Ή Components orientation
πŸ”Ή Wrong placement
πŸ”Ή Solder bridges
πŸ”Ή Insufficient or excessive solder on joints
πŸ”Ή Tombstoning

The working mechanism and process is:

πŸ“· PCB Scanning and Image Capture β†’ πŸ–₯ Image Processing β†’ πŸ” Comparing against Reference β†’ βœ… Identifying are there issues or not

Comparing the present PCBA against the reference, AOI could identify potential defects and alert, so the technicans and quality stuff could react according, such as adjust SMT parameters and settings, before transport the PCBA to next stop.

AOI works by optical, so the inspection is limited by only on the surface and cannot penerate the physical objects, it cannot inspect the solderpads beneth the components, such as BGA, which have to be inspected by X-ray, also AOI is not capable to confirm electrical function, which have to relying on functional testing.

Kyria has AOI station with each SMT line and reflow soldering oven, to inspect the components assembly status right after reflowing soldering, to make sure all PCB are well-assembled and react immediately if any issue spotted.

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