AOI Test

Automated Optical Inspection (AOI) Test

Automated optical inspection (AOI) test is an automated visual inspection of the printed circuit board (PCB) and assembly manufacture where a camera autonomously scans the device under test for both catastrophic failure and quality defects.

Automated optical inspection (AOI) is an automated visual inspection of printed circuit board (PCB) (or LCD, transistor) manufacture where a camera autonomously scans the device under test for both catastrophic failure (e.g. missing component) and quality defects (e.g. fillet size or shape or component skew).

It is commonly used in the manufacturing process because 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-reflow, and post-reflow as well as other states.

Historically, the primary place for AOI systems has been after solder reflow or “post-production.”

Mainly because,post-reflow AOI systems can inspect for most types of defects (component placement, solder shorts, missing solder, etc.) at one place in the line with one single system.

In this way, the faulty boards are reworked and the other boards are sent to the next process stage.

When it comes to PCB fabrication, automated optical inspection (AOI) is an important process used in PCB fabrication and PCB assembly, as well as a test for printed circuit boards.

It plays an effective and accurate role in detecting the electronic assemblies and your PCBs to make sure the product has a high quality leaving the production line and your PCB without any manufacturing faults.

SMT inspection

AOIs for a PCB board with components may inspect the following features:

  • Area defects
  • Billboarding
  • Component offset
  • Component polarity
  • The 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
  • Volume Defects
  • Wrong Part
  • Solder Bridging

Presence of Incoming Material on the board

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 inspection may detect these features:

  • Line width violations
  • Spacing violation
  • Excess copper
  • Missing pad – a feature that should be on the board is missing
  • Short circuits
  • Gold Finger damage
  • Cuts
  • Hole breakage – a drilled hole (via) is outside of its landing pad
  • Wrong mounting components identified

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 testing



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