Automated Optical Inspection

Automated Optical Inspection (AOI) is an automated visual inspection of PCB(or LCD,transistor manufacture) where a camera autonomously scans the device under test for both catastrophic failure (eg. missing component) and quality defects (eg. fillet size/shape or component skew). It is commonly used in the manufacturing process due to the fact it is a non-contact test method. It is implemented at many stages through the manufacturing process including bare board inspection, Solder Paste inspection (SPI), pre- and post-reflow as well as other stages.

SMT inspection

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AOI's for a PCB board with components may inspect the following features:

• Area Defects
• Billboarding
• Component Offset
• Component Polarity
• Component Presence/Absence
• Component Skew
• Excessive Solder Joints
• Flipped component
• Height Defects
• Insufficient Paste around Leads
• Insufficient Solder Joints
• Lifted Leads
• No Population tests
• Paste Registration
• Severely Damaged Components
• Solder Bridges
• Tombstoning
• Volume Defects
• Wrong Part

AOI can be used in the following locations in the SMT lines: post paste, pre-reflow, post-reflow, or wave areas.

Bare PCB inspection

AOI for a bare PCB board insection may detect these features:

• Line width violations.
• Spacing violation.
• Access copper.
• Missing pad. I.e. a feature that should be on the board is missing.
• Shorts circuits.
• Cuts.
• Hole breakage. I.e. a drilled hole (via) is outside of its landing pad.

The triggering of a defects report may be either rule based (e.g. no lines on the board should be smaller than 50μ) or CAD based in which the board is locally compared with the intended design.

This inspection is much more reliable and repeatable than manual visual inspection.

In many cases, smaller circuit board designs are driving up the demand for AOI vs In-Circuit-Test.