4.4 Fire Safety in Thermal Processes

Thermal processing equipment (Reflow ovensOvens, Wave Soldering, Curing Ovens) essentially operates as a controlled fire inside a manufacturing enclosure. The boundary between a functional soldering profile and Wavea solderingcatastrophic machinesfacility containfire heatersis (updefined tostrictly 300°C),by flammablethermal regulation and fuel management. Treat flux residues,residue not as "dirt," but as accumulated fuel waiting for an ignition source.

Fuel Management (Flux Residue)

Vaporized flux condenses on cooler surfaces within the oven tunnel and forcedexhaust air—the perfect fire triangle.

Reflow Oven Protocols

• Flux Management: Flux volatiles condense in the cooler zones of the oven/exhaust.ducting. This buildupcondensate is highly flammable.
  • If Process is Reflow Soldering -> Then implement a preventive maintenance (PM) schedule to scrape/clean tunnel entrance and exit zones.
    • Mandate:Threshold: WeeklyResidue inspectiondepth must never exceed 2 mm.
  • If Process is Wave Soldering -> Then remove dross and cleaningspent offlux exhaustdaily.
    • Risk: ventsTitanium fingers and condensationsolder trapspots operate at > 250˚C. Accumulated paper/flux debris near the pot is requiredan toimmediate preventignition "Flash-off" fires.hazard.
  • Extinguishers:If StandardExhaust dryVelocity powderdrops extinguishers< can5 destroym/s the-> delicateThen opticsinspect andductwork electronicsfor of an SMT machine.blockage.
    • Requirement:Physics: Low flow allows volatile organic compounds (VOCs) to pool, creating an explosive atmosphere inside the oven.

  Pro-Tip: Use thermal imaging cameras during maintenance cycles to identify "hot spots" in the electrical cabinet or heating elements that indicate failing insulation or loose connections before they arc.

  Thermal Runaway Protection

  Software controls can hang or fail. Relying solely on the PLC to control temperature is negligence.

  • If Primary Control Loop fails (Solid State Relay shorts ON) -> Then a dedicated Hardware Over-Temperature Switch must cut main power.
    • Constraint: This switch must be independent of the PLC logic and physically break the contactor coil circuit.
  • If Conveyor stops (Jam/Motor failure) -> Then Heaters must auto-shutoff.
    • Reason: Stationary PCBs under active heaters will char and ignite within seconds.

  Suppression Systems

  Water sprinklers destroy electronics and can cause steam explosions in molten solder.

  • Inside the Machine: Use CO2 or Clean Agent (e.g.,extinguishers. FM-200)These extinguisherssuppress mustfire beby locateddisplacing atoxygen everywithout thermalleaving processingconductive line.residue that destroys the machine's electronics.
• Surrounding Area: Standard building sprinklers are the final defense for the structure, not the machine.

Final Checklist

Risk AreaParameter	PreventiveMetric Action/ Rule	EmergencyCritical ResponseState
OvenOver-Temp ExhaustProtection	Weekly cleaning of flux residueType	CO2Hardware ExtinguisherSwitch (No Powder)Non-Software)
WaveFlux SolderResidue	DrossMax removal (fire risk)Depth	Emergency≤ Stop2 (Cut Power)mm
SprayExhaust CoatingInterlock	Explosion-proof ventilationLogic	Fan Off = Heaters Off
Conveyor Interlock	Auto-suppressionLogic	Stop system= Heaters Off
Extinguisher Type	At Machine	CO2 / Clean Agent
Duct Inspection	Frequency	Quarterly