Conformal Coating Comparison Guide

• Ease of rework
• Simple drying process
• Good moisture resistance
• High Fluorescence level
• Ease of viscosity adjustment

Solvent Evaporation

• High VOC potential
• Difficult to maintain viscosity
• Requires close monitoring of solvent concentration, hence creates a 2-part scenario
• Flammability
• High probability of reversion under temperature and humidity stress conditions

Heat Cure

• Cure is dependent on thickness
• Component mass affects time and temperature of cure process
• Susceptible to cure inhibition
• Shrinkage (3% – 10%), potential for damaging fragile (e.g., glass) components
• Should be used with caution for low temperature components

UV Cure

• One component coatings require accurate application material to avoid shadowed areas
• Two part systems require meter mix equipment
• Some coatings are more difficult to rework
• UV Intensity and Wavelength effects cure
• Some secondary cure mechanisms require heat exposure

• Useful to about 150ƒC [302ƒF]
• Harder durometer, abrasion resistance
• CTE closer to epoxy PCB substrate
• Higher T g
• Good dielectric properties

Solvent Evaporation

• Higher chloride contamination potential
• Process intensive, difficult to maintain viscosity, complex mix ratios
• Potential for high stress during temperature cycling conditions
• Difficult to rework
• High probability of reversion under temperature and humidity stress conditions

Heat Cure

• Cure is dependent on thickness
• Component mass affects time and temperature of cure process
• Selective coating quality (edge definition) could be impacted
• Shrinkage (3% – 10%), potential for damaging fragile (e.g., glass) components
• Should be used with caution for low temperature components

UV Cure

• One component coatings require accurate application material to avoid shadowed areas
• Two part systems require meter mix equipment
• Some coatings are more difficult to rework
• UV Intensity and Wavelength effects cure
• Some secondary cure mechanisms require heat exposure

Catalyzed

• Cure inhibition
• Short work life
• Contamination sensitive
• Difficult to rework
• Pungent odor

• Good dielectric properties
• Good moisture resistance
• Solvent resistance
• Less reversion potential
• Abrasion resistance

Solvent Evaporation

• Moisture affects cure rate and desired properties
• Long complete cure time (up to 30 days)
• Health and safety concerns
• Potential for high stress during temperature cycling conditions
• High probability of reversion under temperature and humidity stress conditions

Heat Cure

• Cure is dependent on thickness
• Component mass affects time and temperature of cure process
• High VOC potential
• Reacts violently with presence of water
• Should be used with caution for low temperature components

UV Cure

• One component coatings require accurate application material to avoid shadowed areas
• Two part systems require meter mix equipment
• Some coatings are more difficult to rework
• UV Intensity and Wavelength effects cure
• Some secondary cure mechanisms require heat exposure

• Stable over wide temperature range (in general, -40ƒC to 200ƒC)[104ƒF to 392ƒF]
• Flexible, provides dampening and impact protection
• Good moisture, humidity, and UV/sunlight resistance
• High dielectric strength
• Low surface energy to enable effective penetration under components

Room Temperature Vulcanization (RTV)

• Requires humidity (minimum 20% RH) to cure and only intermittent solvent resistance
• Low abrasion resistance
• Short pot life
• TCE is ~300-350 ppm/ƒC
• If proper house keeping is not followed, there is a potential for cross contamination

UV Cure

• One component coatings require accurate application material to avoid shadowed areas
• Potential for cure inhibition
• Low abrasion resistance
• UV Intensity and Wavelength affects cure
• Some secondary cure mechanisms react with moisture, this can cause spray valves to become clogged

Catalyzed (Addition)

• Low abrasion resistance
• Potential for cure inhibition
• Adhesion may be difficult
• Only intermittent solvent resistance
• If proper house keeping is not followed, there is a potential for cross contamination

• Excellent uniformity regardless of part geometry ‘ no pinholes, fillets, or bridging
• Chemical inertness/barrier properties ‘ insoluble in organic solvents, acids, or bases, with very low permeability rates
• Minimal added mass and low outgassing
• Biocompatibility allows uses in many medical applications
• Low environmental impact process

Vapor Deposition Polymerization

• Parts are processed by batches in a vacuum chamber, not an in-line process
• Masking required for no-coat areas
• Coating removal and rework generally requires specific equipment, abrasion/micro-blasting most common technique
• Limited UV resistance and operating temperature limit, around 120ƒC [248ƒF] in the presence of oxygen
• Cannot be doped

• Excellent uniformity regardless of part geometry ‘ no pinholes, fillets, or bridging
• Chemical inertness/barrier properties ‘ insoluble in organic solvents, acids, or bases, with very low permeability rates
• High temperature stability (450ƒC [842ƒF]) and increased UV stability
• Low dielectric constant, 2.28
• Low environmental impact process

Vapor Deposition Polymerization

• Parts are processed by batches in a vacuum chamber, not an in-line process
• Masking required for no-coat areas
• Coating removal and rework generally requires specific equipment, abrasion/micro-blasting most common technique
• The coating is deposited at a rate slower than the conventional poly-para-xylelenes
• Requires special deposition equipment different than that for the C, D, and N poly-para-xylelene varieties.

• Low dielectric constant
• High glass temperature
• Low surface energy
• Low water sorption
• Good solvent, oil and common acid resistance

Solution Deposition

• Requires special liquids for polymer swelling
• Limited solubility which limits film thickness
• May require glass temperature anneal
• Requires special surface treatment for greatest adhesion
• Poor resistance to some acids and alkalines

Vacuum Deposition

• Requires pressure of 10 Torr ‘ 5 Torr [0.193 PSI ' 0.097 PSI] or less
• May require glass temperature anneal
• Requires special surface treatment for greatest adhesion
• Poor resistance to some acids and alkalines
• Poor abrasion resistance