Why are Parylene coatings so unique?

  • Parylene is an organic polymer which consists (in its basic form as parylene N) only of the atoms of hydrogen (H) and carbon (C). Parylene is hydrophobic and resistant to almost all chemicals. This applies to other polymers such as PTFE, too, but the special properties result from the exceptional manufacturing technology.
  • Parylene have an economic importance only as thin coatings. The polymer is formed by polymerization of the gaseous monomer on the cold substrate surfaces. All liquid coatings contain gas inclusions and the coating tends to contract locally, also with a low surface tension. This results in forming of gaps, edge loss of the coating and inhomogenous film thicknesses. By the polymerization of parylene directly from the gas phase, the molecules are fitting to one another. There exsists no pores, but a constant film thickness at molecular scale.
  • Parylene polymerizes on cold surfaces. There is no thermal load at the substrates. Almost any material can be coated by Parylene.
  • Parylene coatings have excellent barrier properties against almost all substances. Parylene form a very high and especially reliable protection against chemicals, environmental influences and aging.

What is Parylene?

In 1947, the chemist Michael Szwarc examined  reactions of xylene at high temperatures up to 1000 ° C. He discovered a transparent precipitation on cold surfaces of its apparatus. This thin solid film has been analyzed as poly (p-xylylene). As more effective synthesis process, in 1955, the company Union Carbide introduced the still usual method by pyrolysis of the dimer paracyclophane. Thus had opened the way for commercial applications. Union Carbide had also named the polymer poly(p-xylylene) as parylene, which was easier to handle.

The method works only in the vacuum chamber at a pressure up to about 0.1 mbar.

 

Precursor: DimerAfter pyrolysis: MonomerEnd product: Polymer

exact chemical term

paracyclophane

or

Di-p-xylylene

 

Chinondimethane

or

p-xylylene

 

 Poly(p-xylylene)

handlicherer Begriff:

Parylene-Dimer

 

Parylene-Monomers

 

Parylene N

Manufacturing process for parylene coatings
Manufacturing process for parylene coatings

It actually shows the schematic representation of the production method of the base type Parylene N. There are more parylene types with different properties, which are presented in "Material Properties".

How to produce parylene layers?

A method as shown above, exists for no other material. Therefore it is necessary to have very unique constructed equipment especially for parylene coatings.

What is the performance of Parylene?

Parylene coatings are superior to all other coating methods in the following properties:

  • Continuity of the coating thickness
  • Coverage of edges and spikes
  • Penetration into extremely thin columns
  • Tightness with minimum layer thickness
  • Barrier properties against permeation of gases and liquids
  • Protection against moisture
  • Protection against electrical breakthrough
  • Protection against oxidation
  • Aging resistance and protection against material aging
  • biocompatibility

In addition to the basic type and halogen-free Parylene N, the types Parylene C, Parylene D, Parylene F-VT4 and Parylene F-AF4 are used commercially. All Parylene types have the properties mentioned before.

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 properties.

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.

When do you need Parylene?

  • When electronic components have to fulfill highest safety and durability requirements (Aerospace).
  • When components are exposed to extreme environmental conditions.
  • When very worthy pieces should be kept "forever" (antiques, jewelry).
  • When seals should "never" become brittle.
  • When diffusion should be prevented by walls (pipes, containers).
  • When implanted components should not react with fluids from the human body (Medicine).
  • When sensors should be protected against aggressive media.
  • When metals have to be protected against oxidation.
  • When good lubricity (and low abrasion) is important (catheters, cannulae)
  • high performance and certifications according to US MIL and US NBC (Nuclear Biological and Chemical Contaminations) secure a wide range of applications in military / aerospace applications. Parylene are also UL listed (Underwriters Laboratories) for safety-related applications.
  • FDA Approvement for food contact and USP (United States Pharmacopeia) Class VI certification allow unrestricted contact with foodstuffs, pharmaceuticals and living body tissue, as well as in medicine and pharmacy.