Parylene Coating

Chemical Structures

The Dimer and Polymer Structures of Parylene Variants

Parylene N, C, AF4 are commonly used Parylene powders for nano conformal coating on the market and their structures of dimers and film-forming polymers are shown in the table below:

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Parylene VariantsDimersPolymers
Parylene N
Parylene C
Parylene AF4

Coating Properties

Properties of Parylene Coating

The differences in the chemical structure of parylene N, C, AF4 dimer and their film-forming polymers lead to significant differences in some coating properties. The PTEF (Teflon) segment in the chemical structure of the Parylene AF4 film-forming polymer improves the chemical solvent resistance, acid and alkali corrosion resistance, thermal performance, UV resistance and other properties of the Parylene AF4 nano coating. The properties of Parylene N, C and AF4 nano coatings are classified and compared below.  The data will vary with the actual application, and the data in the table are for reference only.

Electrical Properties

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PropertiesParylene AF4Parylene NParylene C
Dielectric Constant (@ 60Hz/1KHz/1MHz)2.21/2.20/2.172.65/2.65/2.653.15/3.10/2.95
Dissipation Factor (@ 60Hz/1KHz/1MHz)<0.0002/0.002/0.0010.0002/0.0002/0.00060.020/0.019/0.013
Dielectric Strength (V/mil)5,4007,0005,600
Volume Resistivity (Ohm-cm)2.0x10¹⁷1.4x10¹⁷8.8x10¹⁷
Surface Resistivity (Ohms)5.0x10¹⁵1.0x10¹⁵1.0x10¹⁵

Thermal Properties

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PropertiesParylene AF4Parylene NParylene C
Linear Coefficient of Thermal Expansion (CTE) @ 25°C (ppm)366935
Continuous Operating Temp. (°C)3506080
Short-term Operating Temp. (°C)45080100
Thermal Conductivity @ 25°C (W/(m.K))0.0960.1260.084
Specific Heat @ 20°C (J/(g.K))1.040.8370.712
Thermal ShockPASSPASSPASS
Flame ResistanceSelf extinguishingSelf extinguishingSelf extinguishing
UV Exposure Time in air (hrs)Stable up to 2000UnstableUnstable

Gas Permeability @ 25 °C

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PropertiesParylene AF4Parylene NParylene C
N₂ gas permeability (cc.mm)/(m².day.atm)4.83.00.4
O₂ gas permeability (cc.mm)/(m².day.atm)23.515.42.8
CO₂ gas permeability (cc.mm)/(m².day.atm)95.484.33.0
H₂ gas permeability (cc.mm)/(m².day.atm)NA212.643.3

Barrier Properties

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PropertiesParylene AF4Parylene NParylene C
Water Vapor Transmission Rate (g.mm/m²day)0.220.590.08
Water Absorption (% after 24 hrs)<0.01<0.1<0.1

Chemical Resistance

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PropertiesParylene AF4Parylene NParylene C
Coated PCB Salt Fog Test for 144 hrsPASS--
70% Nitric acid, % Swelling @RT00.20.2
70% Nitric acid, % Swelling @75 °C1.2Brittle1.8
95-98% H₂SO₄, % Swelling @RT00.20.4
95-98% H₂SO₄, % Swelling @75 °C2.85.35.1

Mechanical Properties

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PropertiesParylene AF4Parylene NParylene C
Tensile Module (psi)380,000350,000460,000
Tensile Strength (psi)7,5007,00010,000
Yield Strength (psi)5,0006,1008,000
Rockwell HardnessR122R85R80
Yield Elongation (%)2.02.52.9
Elongation to Break (%)Up to 200Up to 250Up to 200
Coefficient of Friction Static/Dynamic0.15/0.130.25/0.250.29/0.29

Other Properties

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PropertiesParylene AF4Parylene NParylene C
Reflection Index (ND23)1.561.661.64
Penetration Ability (aspect ratio)50xdiameter40xdiameter5xdiameter
Water Contact Angle101.83°74.84°78.61°
USP Class VI PolymerYesYesYes
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