Automated Optical Inspection (AOI)
Automated optical inspection (AOI) is an automated visual inspection of printed circuit board (PCB) where a camera autonomously scans for things like missing components and quality defects (see below).
It is commonly used in the manufacturing process because anything can happen during assembly. Sometimes the root cause of an issue is something internal such as a solder paste smudge or something about the PCB layout causes parts to stand up like a tombstone.
Henway uses their AOI machine in a variety of ways including bare board inspection, solder paste inspection (SPI), pre-reflow and post-reflow, through hole inspection, etc.
The AOI machine produces a report that consists of a picture of the circuit board with the problem areas highlighted and a short description of the problem. This sheet can be printed out and taken to the rework station or reworked at the inspection table on the output of the AOI conveyor.
Common PCB AOI inspection items:
Area defects
Billboarding
Component offset
Component polarity
Component presence or 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
Tombstoning
Wrong Part
Solder Bridging
Presence of Foreign Material on the board
Conformal coating coverage
Proper serialization/barcoding
… and much more
Bare PCB inspection
AOI for a bare PCB board inspection may detect these features:
Internal cutout quality
Spacing violation
Excess copper
Missing pad
Short circuits
Gold Finger damage
Cuts
Hole breakage – a drilled hole (via) is outside of its landing pad
Usually we catch issues when making repeat PCB fabrication orders and vendors sometimes panelize boards differently, use the wrong version for PCB production, forget to mill an internal slot, forget to plate an internal slot, etc. Our PCB fabrication vendors are great and mistakes are rare but never zero. This inspection is much more reliable and repeatable than manual visual inspection and catches mistakes before they turn into problems.
Picture of an AOI test report from Henway’s AOI machine.