Coating Chemistries
There are many chemistries of conformal coatings out on the market today. While the "Material Considerations" section below is very important to finding the correct conformal coating, it is also important to find a coating chemistry meeting the application needs. Below are five common strengths for each conformal coating chemistry.
- Acrylic
- Ease of rework
- Simple drying process
- Good moisture resistance
- High Fluorescence level
- Ease of viscosity adjustment
- Epoxy
- Useful to about 150C
- Harder durometer, abrasion resistance
- CTE closer to epoxy PCB substrate
- Higher Tg (Glass transition)
- Good dielectric properties
- Polyurethane
- Good dielectric properties
- Good moisture resistance
- Solvent resistance
- Less reversion potential
- Abrasion resistance
- Silicones
- Stable over wide temperature range (in general, -40C to 200C)
- Flexible, provides dampening and impact protection
- Good moisture resistance
- High dielectric strength
- Low surface energy for better wetting
- Fluorinated or non Fluorinated - Poly-Para-Xylylene (Parylene)
- Excellent uniformity regardless of part geometry
- Chemical inertness
- Minimal added mass and low outgassing
- Low environmental impact process
- Low dielectric constant
- Amorphous Fluoropolymer
- Low dielectric constant
- High glass transition temperature
- Low surface energy
- Low water absorption
- Solvent resistance
The basics of conformal coating processing can be understood from a presentation available giving a summary of the areas covered above.
Read more about this topic: Conformal Coating
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