6.4 Environmental Controls (Temperature/Humidity, Cabinets, Monitoring)

The warehouse environment is a functional component of the manufacturing process. Poor storage conditions degrade material chemically and physically long before it hits the production line. This damage—moisture saturation, oxidation, adhesive curing—is invisible to the naked eye. You cannot "inspect" moisture content; you can only control the history of the part. If environmental control fails, the result is latent field failure or massive yield loss at reflow.

Physics of Failure

Understand what you are preventing. "Room temperature" is not a specification; it is a variable.

• Moisture Absorption (Popcorning): Plastic encapsulants absorb humidity from the air. During reflow (240°C+), this trapped water turns to steam, expanding instantly and cracking the package (delamination).
• Oxidation: High humidity accelerates the formation of oxides on termination leads and PCB pads. This acts as an insulator, preventing proper solder wetting.
• Polymer Degradation: Adhesives, solder paste, and pre-pregs begin to cure or separate if exposed to heat. This is irreversible.

Storage Class Matrix

Define where materials live based on their chemistry, not their size.

Monitoring & Alarms

Do not rely on paper charts marked once a day by a human. Data must be continuous and actionable.

• Automated Logging: Install digital data loggers in all zones (Ambient, Fridges, Dry Cabinets). Sampling rate: Every 15–30 minutes.
• The Alarm Rule:
  • If Temp/RH breaches limit for > 30 mins → Then Trigger alert (SMS/Email/Light).
  • If Fridge fails over the weekend → Then System must flag the duration of the excursion.
• Dry Cabinet Hygiene:
  • Alarms must trigger if the door is left ajar > 2 minutes.
  • Recovery time is critical: The cabinet must return to <5% RH within 15 minutes of door closure.

Nonconformance & Excursions

Define what happens when the environment fails.

• Scenario: A fridge containing Solder Paste loses power for 12 hours.
  • Bad Action: "It feels cool still, put it back."
  • Correct Action: Quarantine. Move to MRB. Engineering must review manufacturer specs (e.g., "Stable for 24h at 25°C"). If unknown, Scrap.
• Scenario: Dry Cabinet rises to 30% RH for a shift.
  • Action: All open reels inside are now "Exposed." You must add that time to their Floor Life clock. If tracking is impossible, Bake all contents to reset.
• Missing Data:
  • If logs are missing for a period → Then assume the worst-case scenario. You cannot prove the material is safe, so you must re-verify or bake.

Final Checklist