The separation is carried out by polymerisation using a vacuum-assisted coating process known as chemical vapour deposition (CVD). The "dimer" (solid [2,2]-p-cyclophane), which is present in a powder-like basic form, is first sublimated in the evaporator.
The thermal decomposition of the relatively inert "dimer gas" takes place with the aid of a pyrolysis tube at approx. 650 °C and results in the formation of highly reactive monomers. The process pressure depends on the dimer and system type used and is approx. 0.02 - 0.1 mbar. Through diffusion, the reactive monomers reach the following vacuum chamber, in which the coating material is placed on a rotating frame.
The reactive monomers preferably polymerize to thin layers of poly(para-xylylene) or parylene on cold surfaces. Since not all monomers polymerise in the chamber, subsequent coating of the vacuum pump must be prevented. Therefore it is necessary to integrate a cryo trap into the system. The cryo trap is simply filled with liquid nitrogen during the process time so that the residual monomers polymerise in the cryo trap, ensuring the functionality of the pump.
Applications
Easy coating in a wide range of applications
Parylene is the short designation of the polymer group of poly(para-xylylenes). The polymers consist of different substituted para-xylylenes. The original basis for coating are dimers. This is a molecular compound consisting of two identical sub-units, the so-called monomers.
The unique properties of parylene:
- constant absolute thickness of coating, independent of the substrate geometry
- pinhole-free from under 1 micron
- excellent penetration in crevices and holes
- unparalleled barrier properties (especially for parylene C)
- insolubility
- food safety and biocompatibility
- no environmental impact
- extremely high temperature resistance (Parylene F-AF4)
