Troubleshooting / Conformal coating machine

Conformal Coating Machine Troubleshooting

The most common conformal coating machine problems on the plant floor, with the likely causes and the fix for each. Part of the OEE Lab troubleshooting directory.

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Problems on this page:

Coating in keep-out areasBubbles in the coatingGaps or thin coverageNozzle cloggingCoating not curingDewetting or fisheyesViscosity driftingThickness out of specificationCoating creeping under componentsInspection under UV unreliable

Coating in keep-out areas

Hits OEE: Quality

Symptoms: Coating reaches connectors, test points or other areas that must stay clean.

Program offsets wrong for the board revision
Check the program against the current board revision and the keep-out drawing.
Spray pattern wider than set
Check the nozzle and the pattern width with a test card.
Nozzle dripping at the end of a path
Check the valve and the cut-off timing.
Masking missing or lifting
Check the masking before coating.

Prevention: Keep-out areas inspected on the first board of each run.

Bubbles in the coating

Hits OEE: Quality

Symptoms: Bubbles are seen under UV inspection.

Coating too thick in one pass
Apply thinner layers.
Viscosity too high
Check the viscosity and temperature.
Cure starting too fast
Check the flash-off time before curing.
Air in the fluid line
Purge the line.

Prevention: Bubble check under UV on samples.

Gaps or thin coverage

Hits OEE: Quality

Symptoms: Parts of the board that need coating are bare or too thin.

Tall components shadowing areas
Use tilted spray paths.
Flow rate low
Check the flow.
Path missing in the program
Add the missing path to the program.
Nozzle partly blocked
Clean the nozzle.

Prevention: Coverage checked under UV on samples.

Nozzle clogging

Hits OEE: Availability

Symptoms: The nozzle spits, sprays unevenly, or blocks.

Coating drying in the nozzle during pauses
Use the nozzle purge or cap during pauses.
Material past its pot life
Use material within its life.
Filter missing
Fit a fluid filter.
Cleaning not done
Clean the nozzle at the end of the shift.

Prevention: Nozzle cleaning on the shift checklist.

Coating not curing

Hits OEE: Quality

Symptoms: The coating stays tacky after the cure step.

UV lamp intensity low
Measure the lamp output and replace aged lamps.
Oven temperature or time wrong
Check the cure profile.
Humidity too low for moisture cure materials
Check the room conditions.
Mix ratio wrong for two-part materials
Check the dispensing ratio.

Prevention: Cure check on samples each shift.

Dewetting or fisheyes

Hits OEE: Quality

Symptoms: The coating pulls away from areas of the board.

Flux residue on the board
Check the cleaning after soldering.
Release agents or silicone contamination
Find and remove the source.
Handling with bare hands
Use gloves.
Board not dry after cleaning
Dry boards fully.

Prevention: Cleanliness tests on boards before coating.

Viscosity drifting

Hits OEE: Quality

Symptoms: Coating thickness changes during the shift.

Solvent evaporating from the reservoir
Keep the reservoir closed.
Room temperature changing
Control the room temperature.
Material from different lots mixed
Do not mix lots.
No viscosity checks
Check viscosity at set times.

Prevention: Viscosity logged at start-up and mid-shift.

Thickness out of specification

Hits OEE: Quality

Symptoms: Measured thickness is outside the limits.

Flow or speed settings changed
Check the program parameters.
Number of passes wrong
Set the number of passes in the program.
Measurement method inconsistent
Use a defined method on test coupons.
Viscosity changed
Check the viscosity.

Prevention: Thickness measured on coupons each run.

Coating creeping under components

Hits OEE: Quality

Symptoms: Coating wicks under connectors or into sockets and relays.

Material too thin for the area
Use a thicker material or a dam around sensitive parts, because thin coating flows into gaps by capillary action.
Too much coating near the part
Reduce the flow or move the spray path away from the component.
Components not sealed against coating
Use sealed components or mask them before coating.
Board tilted during curing
Keep boards level until the coating has set.

Prevention: Connector function checked on the first boards of a new product.

Inspection under UV unreliable

Hits OEE: Quality

Symptoms: Coverage checks give different answers between inspectors or shifts.

UV inspection lamp weak or the wrong type
Use the lamp the material supplier recommends and replace aged lamps.
Room light too bright during inspection
Inspect in a darkened booth so the tracer shows clearly.
No reference boards
Keep approved good and bad reference boards at the station.
Material without a UV tracer
Use a material with a tracer where inspection relies on it.

Prevention: Inspection method written with reference images.

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

Related equipment guides: selective soldering machine · reflow oven · vision inspection · wave solder machine · depaneling router · ultrasonic cleaner · crimping machine

Stop the same fault coming back

Recurring conformal coating 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.

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Related tools: full troubleshooting directory · OEE calculator · downtime cost · MTBF / MTTR · glossary

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