AOI Machine Troubleshooting: Causes & Fixes

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Problems on this page:

Too many false calls Real defects escaping Boards not transported or clamped Fiducial recognition failing Slow programme changeovers Camera or lighting fault Review station holding up the line Results not used to fix the process Measurement drifting

Too many false calls

Hits OEE: Performance

Symptoms: The AOI flags many good boards and the review station becomes the bottleneck.

Thresholds set too tight

Tune the thresholds on the components that cause most false calls.

Library not updated for a new component supplier

Update the component library when the supplier or package look changes.

Board colour or finish varying

Teach the variation into the programme.

Lighting settings not suited to the board

Adjust the lighting for the board finish.

Prevention: False call rate tracked per programme.

Real defects escaping

Hits OEE: Quality

Symptoms: Defects are found later in test or by the customer on boards the AOI passed.

Thresholds set too loose

Check the thresholds on the escaped defect type.

Component not in the inspection programme

Check the programme covers every component.

Tall parts shadowing smaller ones

Use angled cameras or extra views.

Wrong library entry used

Check the library entry for the component.

Prevention: Escapes fed back to programme owners within a day.

Boards not transported or clamped

Hits OEE: Availability

Symptoms: Boards stop at the entry, are not clamped or jam in the conveyor.

Conveyor width not set for the board

Set the width at each changeover.

Board warped

Check board flatness from the reflow oven.

Board sensors dirty

Clean the sensors.

Clamp settings wrong

Check the clamp for the board thickness.

Prevention: Conveyor width on the changeover checklist.

Fiducial recognition failing

Hits OEE: Availability

Symptoms: The machine cannot find the fiducials and stops or skips boards.

Fiducials dirty or damaged

Check fiducials on the boards.

Lighting settings changed

Restore the programme lighting.

Wrong fiducials in the programme

Check the programme against the board.

Board placed with a large offset

Check the board stop position.

Prevention: Fiducial failures recorded per programme.

Slow programme changeovers

Hits OEE: Performance

Symptoms: New boards wait for programmes to be written or tuned.

Programmes started late

Prepare programmes from the design data before the first board arrives.

Library missing components

Keep the library up to date.

Tuning done on the line

Tune offline where possible.

Only one person can programme

Train more programmers.

Prevention: Programme readiness checked before each new job.

Camera or lighting fault

Hits OEE: Availability

Symptoms: Images are dark or blurred, or the machine reports a camera fault.

Lighting unit failing

Replace failing lights, since weak lighting changes every inspection result.

Camera lens dirty

Clean the lens as the maker describes, with the machine stopped.

Camera calibration lost after a knock or service

Run the camera calibration routine and check it against the reference board.

Camera cable damaged in the cable chain

Check the camera cables for wear where they flex.

Prevention: Camera calibration run on a fixed schedule.

Review station holding up the line

Hits OEE: Performance

Symptoms: Boards queue at the review station and the line slows to the reviewer pace.

Too many false calls reaching review

Reduce false calls at the source by tuning the programme.

Review images unclear

Improve the image settings so reviewers can decide quickly.

Reviewers not trained on the defect standards

Train reviewers with examples of good and bad joints.

No buffer between the AOI and review

Add a small buffer so short review peaks do not stop the line.

Prevention: Review time per board recorded each shift.

Results not used to fix the process

Hits OEE: Quality

Symptoms: The same defects appear week after week.

Defect data not reviewed

Review the top defects weekly with the process owners.

Defects not linked to the step that caused them

Classify defects by cause.

No feedback to printing or placement

Send results to those steps.

Data stored only on the machine

Export data to the quality system.

Prevention: Top defects reviewed every week.

Measurement drifting

Hits OEE: Quality

Symptoms: Position or height readings shift slowly over weeks, and false calls or escapes creep up.

Calibration overdue

Run the calibration routine on the schedule the maker sets.

Room temperature changing

Keep the room temperature steady around the machine.

Mechanical wear in the axes

Have the axes serviced and checked.

Reference board damaged

Replace a scratched or warped reference board.

Prevention: Reference board run at the start of each day.

Guidance only. Always follow lockout/tagout and your site's safe-work procedures, and verify against OEM manuals before acting.

Related equipment guides: pick and place · reflow oven · SMT stencil printer · vision inspection · X-ray inspection

Stop the same fault coming back

Recurring AOI machine stops usually trace to a cause you cannot see by hand. The partner we recommend is Fabrico: it tracks OEE and downtime live from PLCs, IoT sensors or AI cameras; where cameras are fitted, the video of a stop sits next to its machine data so the cause can be reviewed; and a technician opens the work order from the stop in the same system. Data is hosted in the AWS EU region, and Fabrico and the company behind it hold ISO/IEC 27001, ISO/IEC 20000-1 and ISO 9001.

Book a Fabrico demo

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Methods that cut recurring stops: the six big losses · root cause analysis · preventive vs predictive maintenance · TPM · SMED & changeover