4.2 Preventive Maintenance (PM) Planning

Facility downtime is production downtime. In high-precision electronics manufacturing, facility systems are not passive infrastructure but active process variables. A failure in compressed air filtration halts pick-and-place nozzles; a lapse in ESD ground maintenance compromises component integrity invisible to visual inspection. This chapter mandates the preventive maintenance (PM) schedules and technical actions required to guarantee system reliability and process stability.

Electrical Distribution & UPS

Unplanned power interruptions and "dirty" power cause logic resets in SMT equipment and corrupt reflow profiles. Maintenance focuses on thermal integrity and backup reliability.

• Thermographic Inspection: Conduct infrared (IR) scanning of all distribution panels, switchgear, and bus ducts annually.
  • Mandate: Investigate and re-torque any connection showing a >5 C rise over ambient or >2 C variance between phases.
• UPS Systems:
  • Battery Impedance: Measure internal impedance of individual battery blocks quarterly. Replace entire strings if impedance deviates >30% from baseline.
  • Transfer Test: Verify static bypass switch operation and offline transfer speeds annually to ensure <10ms transition.
• Grounding: Inspect main earthing pits and bonding cables annually. Clean oxidation from busbars and retighten mechanical lugs to maintain low-impedance paths.

Compressed Air Systems

Pneumatic systems in SMT lines (solenoids, vacuum generators) require air that is mechanically clean and dry. Maintenance prevents oil carryover and moisture saturation.

• Filtration:
  • Pre/Post Filters: Monitor differential pressure gauges weekly. Replace elements immediately if differential pressure exceeds 0.7 bar (10 psi) or every 6 months, whichever comes first.
  • Auto-Drains: Test zero-loss drains on receiver tanks and dryers weekly to ensure condensate ejection is functional.
• Refrigerated Dryers:
  • Condenser Coils: Clean condenser fins monthly using compressed air to prevent high-pressure trips.
  • Refrigerant: Check sight glass for moisture indication and refrigerant levels monthly.
• Compressor: Sample oil quarterly for total acid number (TAN) and particulate count. Change oil and air/oil separators based on hours run (typically 4,000 – 8,000 hours).

HVAC Hardware Maintenance

While setpoints are covered in Environmental Control, the hardware must be maintained to hold those targets without oscillation.

• Air Handlers (AHU):
  • Belts: Check drive belt tension monthly. Replace belts showing cracking or glazing. Improper tension causes fan speed fluctuation and airflow instability.
  • Coils: Chemically clean evaporator and condenser coils semi-annually to maintain heat transfer efficiency.
• Sensors: Calibrate wall-mounted temperature and humidity sensors annually against a NIST-traceable reference standard.
  • Drift Limit: Recalibrate or replace sensors drifting >2% RH or >0.5 C.
• Steam Humidifiers: Inspect steam cylinders monthly. Replace cylinder when scale buildup covers >50% of electrodes or amperage draw drops below specification.

ESD Infrastructure Upkeep

Static control systems degrade with wear and dirt accumulation.

• ESD Flooring:
  • Deep Clean: Scrub floors quarterly with ESD-specific neutral cleaner. Do not use standard wax or sealers, which create insulative layers.
  • Surface Repair: Patch gouges or cracks immediately with conductive epoxy to maintain the equipotential plane.
• Ionizers:
  • Emitter Pins: Clean emitter points on overhead and benchtop ionizers monthly. Oxidized or blunted pins reduce ion output and offset balance.
  • Fan Filters: Clean foam intake filters on ionizing blowers monthly to prevent dust recirculation onto PCBA surfaces.

Final Checklist

System	Maintenance Action	Frequency	Critical Failure Limit
Power	IR Scan Panels	Annually	>5 C rise over ambient
Power	UPS Battery Impedance	Quarterly	>30% deviation
Air	Replace Particulate Filters	6 Months	>0.7 bar diff. pressure
Air	Test Auto-Drains	Weekly	Blocked/Stuck Open
HVAC	Calibrate Temp/RH Sensors	Annually	>2% RH drift
HVAC	Tension Fan Belts	Monthly	Slippage/Glazing
ESD	Clean Ionizer Pins	Monthly	Visible Oxidation
ESD	Deep Clean Floor	Quarterly	No Wax/Sealer