Parylene is the generic name for a family of polymers called the poly(para-xylylene) derivatives. Mainly five grades are used at industrial scale :
Deposited at low pressure and low temperature, Parylene forms a transparent and conformal pinhole-free coating with a wide range of thickness (from 50 nm to 50µm).
The combination of these qualities makes it an extremely interesting player in the most demanding technological fields, including medical, electronics, space and aeronautics and micro and nanotechnologies.
Parylene coatings are deposited in vacuum using a batch process involving the condensation and polymerization of gaseous monomers, similar to Chemical Vapor Deposition (CVD). Polymerization occurs at room temperature with a conversion rate of nearly 100% and without any solvents, initiators, or catalysts. This results in a high-molecular-weight linear and semi-crystalline polymer. High quality coatings and a reproducible process, require strict pressure and temperature control of all the vacuum reactor subassemblies.
The vacuum deposition process, known as the Gorham process, uses dimer powders or precursor. These dimers are sublimated at 80-150°C and then go through a pyrolysis oven at 600-700°C where thermal cracking occurs, this produces highly reactive monomer vapors. After entering the low temperature deposition chamber, the gaseous monomers will condensate and spontaneously polymerize on any surface, leading to a transparent and conformal Parylene (polymer) coating. Gases in excess, are pumped out, and remove by a cold trap (e.g. liquid nitrogen).
In tumbling process (T), the components to be treated are placed in a slowly rotating barrel. The type of equipment allows the pieces to be completely covered with Parylene and is generally used for small, simple pieces that are not mechanically fragile. Very large volumes can be produced this way at low costs.
In the standard process (S), the components to be treated are hung or set on a rotating carousel. It can be used for any type and almost any parts dimensions that fit into the treatment chamber. Best encapsulation performances coatings can be obtained this way.