Troubleshooting / Selective soldering machine

Selective Soldering Machine Troubleshooting

The most common selective soldering 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:

Insufficient hole fillSolder bridgingSolder balls on the boardNozzle losing wettingFlux problemsDross and solder level problemsBoard warping or moving in the fixtureSolder temperature unstableIcicles or spikes on the leadsRobot path or board position errors

Insufficient hole fill

Hits OEE: Quality

Symptoms: Solder does not rise fully through the plated holes.

Preheat too low
Raise the preheat so the board reaches the profile temperature.
Contact time too short
Slow the robot path or increase dwell.
Flux not reaching the hole
Check the flux nozzle and the flux amount.
Heavy copper planes taking heat
Adjust the profile for heavy copper boards.

Prevention: Hole fill inspected on first boards of each program.

Solder bridging

Hits OEE: Quality

Symptoms: Solder joins neighbouring pins.

Drag-off angle or speed wrong
Adjust the robot path at the end of the row.
Too little flux
Check the flux deposit.
Solder temperature low
Check the pot temperature.
Nozzle too large for the pitch
Use a smaller nozzle.

Prevention: Program parameters locked after approval.

Solder balls on the board

Hits OEE: Quality

Symptoms: Small balls of solder stick to the board.

Flux spreading too wide
Reduce the flux and check the nozzle.
Moisture in the board
Bake boards that have taken up moisture.
Solder wave turbulent
Check the pump speed.
Nitrogen flow wrong
Check the nitrogen flow.

Prevention: Board cleanliness checked on samples.

Nozzle losing wetting

Hits OEE: Availability

Symptoms: Solder no longer flows evenly over the nozzle.

Nozzle oxidised
Clean and reactivate the nozzle as the maker describes.
Nitrogen supply low
Check the nitrogen flow and purity.
Nozzle worn
Replace the nozzle.
Dross on the nozzle
Clean the nozzle more often.

Prevention: Nozzle wetting checked each shift.

Flux problems

Hits OEE: Quality

Symptoms: Too much, too little or misplaced flux.

Flux nozzle blocked
Clean the flux nozzle.
Flux pressure or pulse wrong
Check the flux settings.
Flux contaminated or old
Replace the flux.
Flux path not programmed correctly
Check the program path.

Prevention: Flux deposit test at each shift.

Dross and solder level problems

Hits OEE: Availability

Symptoms: Dross builds up or the solder level drops.

Nitrogen cover low
Check the nitrogen.
Solder not topped up
Use automatic wire feed or top up on schedule.
Pot temperature too high
Check the temperature setting.
Dross not removed
Remove dross on the schedule.

Prevention: Solder level and dross removal on the shift checklist.

Board warping or moving in the fixture

Hits OEE: Quality

Symptoms: Joints vary across the board because it bends or shifts.

Fixture not supporting the board
Add supports to the fixture.
Board heated unevenly
Check the preheat.
Board clamps worn
Replace the clamps.
Thin board without stiffener
Use a carrier.

Prevention: Fixtures inspected weekly.

Solder temperature unstable

Hits OEE: Quality

Symptoms: Joint quality changes during the run.

Heater fault
Check the heaters.
Sensor fault
Calibrate the sensor.
Large solder top-ups
Feed solder in small amounts.
Controller tuning
Check the control loop.

Prevention: Solder temperature checked with a separate probe weekly.

Icicles or spikes on the leads

Hits OEE: Quality

Symptoms: Sharp points of solder are left on the component leads after soldering.

Drag-off speed or angle wrong
Adjust the robot path so the board leaves the wave cleanly.
Solder temperature too low
Check the pot temperature against the profile.
Flux used up before the joint is finished
Increase the flux or check its activity.
Nitrogen cover too low
Check the nitrogen flow and purity at the nozzle.

Prevention: Joint inspection on first boards of each program.

Robot path or board position errors

Hits OEE: Quality

Symptoms: The nozzle solders beside the joint or touches parts it should miss.

Fiducials not recognised
Clean the camera and check the fiducial settings.
Board not seated in the fixture
Check the fixture locators and clamps.
Axis calibration drifted
Run the calibration routine.
Program offsets wrong after a revision
Check the program against the current board revision.

Prevention: Program proved on a first board after every revision change.

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

Related equipment guides: wave solder machine · reflow oven · pick and place · SMT stencil printer · nitrogen generator · conformal coating machine · coil winding machine · crimping machine

Stop the same fault coming back

Recurring selective soldering 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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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