In outdoor environments, electronic control boards are susceptible to moisture, rain, and temperature variations, which can lead to corrosion. Even if the enclosure uses rubber seals at both ends, practical tests show that temperature changes can still allow water vapor to enter.
Causes:
- Temperature differences cause internal pressure fluctuations (positive/negative), drawing in external moisture.
- Residual moisture inside the enclosure condenses when cooled.
- Traditional sealing can block liquid water but cannot prevent water vapor infiltration.
To provide long-term protection for electronic components, it is recommended to combine the following approaches:
- Material: PTFE microporous membrane
- Functions:
- Balances internal and external pressure, preventing moisture intake due to temperature changes
- Blocks liquid water from entering
- Specifications:
- Pore size: 0.2–0.5 μm
- Air permeability: ≥ 2000 g/m²/day
- Installation:
- Hydrophobic side facing outward, protective layer facing inward
- Can be fixed using epoxy or silicone adhesive
- For industrial mass production, heat-welded membranes with larger holes can ensure higher ventilation efficiency
- Notes:
- Apply heat evenly if using heat-welded method to avoid damaging micropores
- Membrane edges should extend beyond the hole to form a complete sealed area
- Options: Acrylic, Polyurethane, Silicone
- Functions:
- Prevents direct moisture contact with components
- Enhances reliability when used together with desiccants
- Notes:
- Apply evenly without affecting component heat dissipation or connections
- Options: Silica gel, molecular sieves
- Function: Absorb residual moisture inside the enclosure and reduce condensation risk
- Installation:
- Place on top or bottom of enclosure interior
- Check and replace regularly
- Material:
- PC / ABS with UV stabilizer, wide temperature tolerance
- Design considerations:
- Minimize internal air volume
- Rubber seals rated IP67/IP68, suitable temperature range for outdoor use
- Double sealing: inner rubber gasket + outer silicone seal
- Cable holes use waterproof grommets + membranes
- Vacuum or nitrogen filling to reduce initial moisture
- Heating elements to prevent condensation (for extreme temperature variations)
- Full PCB potting (PU / Epoxy / Silicone) – maintenance-free but highly reliable
| Method | Characteristics | Advantages | Disadvantages |
|---|---|---|---|
| Adhesive Fix | Membrane slightly larger, fixed with epoxy/silicone | Easy maintenance, replaceable | Ventilation limited by hole size |
| Heat Weld | Membrane larger than hole, heat-welded to enclosure | High ventilation efficiency, suitable for mass production | Difficult to maintain, must control temperature to avoid micropore damage |
| Small Hole + Adhesive | DIY or maintenance-focused | Simple, low cost | Pressure equalization is slow; small holes may still create negative pressure |
- Relying solely on rubber seals is insufficient to prevent moisture ingress in outdoor enclosures.
- Waterproof breathable membranes are the core solution, balancing pressure and blocking liquid water.
- Combining PCB conformal coating and desiccants provides long-term protection for electronic components.
- Industrial production should use heat-welded large-hole membranes; DIY or maintenance applications can use adhesive-fixed membranes.
- Advanced applications can adopt potting or nitrogen filling to meet extreme outdoor conditions.
- Determine enclosure size and internal air volume
- Select appropriate membrane pore size, dimensions, and mounting method
- Apply PCB conformal coating
- Place desiccant inside the enclosure
- Install the enclosure, attach the membrane and fix it
- Test under temperature cycling, rain exposure, and humidity conditions
- Adjust hole size or membrane count according to test results