What is AOI (Automated Optical Inspection)? How it works, detectable defects, AOI vs. X-ray vs. ICT comparison, and its importance for quality.
What is AOI?
AOI stands for Automated Optical Inspection – a camera-based quality control system that scans assembled PCBs and compares them against a reference dataset to detect defects. AOI is standard in professional PCBA manufacturing.
How AOI Systems Work
Modern AOI systems use high-resolution cameras (up to 15MP), multiple lighting angles, 3D inspection, and AI-powered image processing algorithms. Inspection takes seconds per assembly with consistently high reliability.
Detectable Defects
AOI detects: missing or misplaced components, wrong polarity, solder bridges, cold joints, insufficient or excess solder, tombstoning, contamination, and damaged traces.
AOI vs. X-ray vs. ICT
AOI (optical) is cost-effective for visible defects. X-ray is needed for hidden joints under BGA/QFN packages. ICT (electrical testing) detects shorts and opens. For most assemblies, AOI is sufficient. At professional EMS providers, AOI is standard for every assembly.
Importance for Quality
AOI is a key element in the zero-defect strategy of modern EMS providers:
- 100% inspection: Every single assembly is inspected – not just random samples
- Traceability: Defects are documented and used for process optimization
- Early detection: Systematic defects are identified before larger batches are affected
- Cost reduction: Defects are detected immediately after placement – rework is cheap, field failures are expensive
At professional EMS providers, 3D-AOI inspection is standard for every assembly – regardless of batch size. This ensures the highest quality from the first prototype board through high-volume production.
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