Conformal Coating Comparison Guide

The following guide is only general in nature and serves as a broad comparison of strengths and weaknesses.

ACRYLIC

5 Strengths of Coating Type

5 Weaknesses of Cure Type

  • 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

EPOXY

5 Strengths of Coating Type

5 Weaknesses of Cure Type

  • 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

POLYURETHANE

5 Strengths of Coating Type

5 Weaknesses of Cure Type

  • 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

SILICONES

5 Strengths of Coating Type

5 Weaknesses of Cure Type

  • 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

POLY-PARA-XYLELENE C, D, N

5 Strengths of Coating Type

5 Weaknesses of Cure Type

  • 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

FLUORINATED POLY-PARA-XYLELENE

5 Strengths of Coating Type

5 Weaknesses of Cure Type

  • 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.

AMORPHOUS FLUOROPOLYMER

5 Strengths of Coating Type

5 Weaknesses of Cure Type

  • 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