The properties of parylene

Parylene are derivatives of benzene. The basic form of Parylene N consists of a benzene molecule. At the benzene ring, at two corners, each hydrogen atom is replaced by a CH2 group. The prefix "para" (abbreviated "p") indicates that these two CH2 groups are attached to the opposite corners of the benzene hexagon.

Parylene N is therefore a pure hydrocarbon.

But one or more hydrogen atoms can be replaced by halogen atoms at the Parylene molecule. Halogens are the chemical elements fluorine, chlorine, bromine and iodine. Thus, a variety of parylene derivatives can be formed theoretically. Only the types parylene N, parylene C, parylene D and parylene F-VT4 are of practical importance. In addition, there is the Parylene F-AF4.

It is possible to deposit all these parylene types in our systems, with the exception of parylene HT. This unique type should be only deposited by P260 which is equipped with a butterfly valve. This unique type should be only deposited by P260 which is equipped with a butterfly valve. The different parylene types posses quite similar characteristics. But if special requirements are needed, e.g. regarding high-temperature stability, electrical properties or barrier properties, so the Parylene type should be chosen with the most suitable profile of properties.

Monomer units of Parylene types used industrially
Monomer units of Parylene types used industrially

Characteristic properties of Parylene:

Parylene N

Basic model, made up only of the atoms of hydrogen and carbon. But not the most common type. Extraordinary good penetration in crevices and holes. Optimum dielectric properties and dielectric strength and therefore preferred for the coating of electronic components and assemblies. Lowest friction coefficient, popular for application of catheters.

Parylene C

The most utilized product with excellent barrier properties. High moisture protection and supported by the good hydrophobic properties. High elasticity, therefore suitable coating for plastics and rubbers. Low coefficient of friction. High deposition rate (up to 10 microns / h).

Parylene D

Used for a long time, due to its elevated temperature stability. But it is also very hydrophobic. Used for protecting electronic components in the aerospace industry.

Parylene F-VT4:

Since, it withstands thermally even higher loads than Parylene D, it displaces this increasingly in applications with higher temperature load. It is much cheaper than Parylene HT.

Parylene F-AF4:

By far the highest temperature stability of all Parylene types. In addition, this type is very insensitive to aggressive radiation exposure, especially to UV. The most expensive version, therefore only used when these special properties are necessarily required.

 

 

Perfect conformal coating

In contrast to liquid applied coatings, the monomers from the gas phase reach those substrate areas that remain beyond the reach of liquid based coatings.

 

 

Good for health and the environment

The raw material is always the pure dimer. Normally no modifications are carried out during parylene coating process by additives, stabilizers or alloys. Therefore table values are valid for parylene types of all manufacturers. Nevertheless, there are quality differences. Excellent parylene coatings can be are achieved through extreme purity of the dimer.

Parylene coatings are chemically very inert, and do not contain foreign materials, so they are classified as non-toxic and are not dangerous to health. Parylene fullfill all requirements regarding food authenticity and biocompatibility. There is no risk to drinking water and environmental pollution. Parylene also comply with the European RoHS directive 2002/95 / EC (Restriction of Hazardous Substances Directive)

Properties of Parylene

    Parylene N Parylene C Parylene D Parylene F-VT4 Parylene F-AF4
Property Unit Poly (para-xylylene)       Poly(monochloro-para-xylylene) Poly(dichloro-para-xylylene) Poly(tetrafluoro-para-xylylene) F-VT4: Substitution of 4 H atoms by 4 F atoms at the benzoe ring Poly(tetrafluoro-para-xylylene) F-AF4: Substitution of 4 H atoms by 4 F atoms at the additional groups
Density g/cm³ 1,11 1,29 1,42 ~1,6 ~1,51
Refractive index (In plane) 1,66 1,64 1,67 1,57 1,56
Tensile Modulus [GPa] 2,4 3,2 2,8 3,0 2,6
Yield Strength [MPa] 42 55 60 52 35
Tensile Strength [MPa] 45 70 75 55 52
Hardness, Rockwell [HR] 85 80 80 - 122
Yield Elongation [%] 2,5 2,9 3,0 2,5 2,0
Elongation to break [%] 30 200 10 10-50 10
Static coefficient of friction   0,25 0,29 0,35 0,39 0,15
Dynamic coefficient of friction   0,25 0,29 0,31 0,35 0,13
Durable Heat Resistance [°C] 80 100 120 140 350
Temporary peak temperature [°C] 95 115 135 250 450
Melting point [°C] 420 290 380 - ≤ 500
Dielectric constant (1 MHz)   2,66 2,95 2,80 2,35 2,17
Dissipation Factor (1 MHz)   0,001 0,013 0,002 0,008 0.002
Dielctric strength [MV/cm] 300 185-220 215 - 225
Volume resistivity [23 °C, 50 %RH, Ω∙cm ] 1,4E+17 8,8E+16 2,0E+16 1,1E+17 2,0E+17
Surface resistivity [23 °C, 50 %RH, Ω]   1,0E+13 1,0E+14 5,0E+16 4,7E+17 5,0E+15
Linear coeff of expansion [µm/m∙°C]        69 35 38 - 36
Heat cpacity [25 °C, J/(g∙K)] 1,3 1,0 0,8 - 1,0
Thermal conductivity [W/m-K] 0,13 0,08 - - 0,10

[1] W.Beach, C. Lee, and D. Bassett, Encyclopedia of Polymer Science and Engineering (Wiley, New York, 1985), 17, 990
[2] J.B. Fortin, Poly-para-xylylene Thin Films: A Study of the Deposition Chemistry, Kinetics, Film Properties, and Film Stability, Ph.D. Thesis, rensselaer Polytechnic
[3] F.E. Cariou, D.J. Vally, and W.E. Loeb, IEEE Transactions on Biomedical Engineering 33(2), 202 (1992).
[4] Structural and dielectric properties of parylene-VT4 thin films Article (PDF Available) in Materials Chemistry and Physics 143(3):908–914 · February 2014 with 71
[5] Data from www.matweb.com Material Property Data