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).