The parylene coating process takes place at room temperature so that there is no thermal stress on the product. The same is physically stable and an inert product within the temperature range. It also provides a friction coefficient of 0.25-0.30 and excellent protection from salt spray, moisture, corrosive elements, etc., existing in the work environment.
The polymers are deposited from the vapor phase, where all sides of the object are encapsulated to achieve a uniform coated surface. It helps to deliver a truly conformal coating.
The parylene coating process includes three stages -
- Sublimation at vacuum at 120 C. It is done by using the stable crystalline dimer di-p-xylylene that delivers vapors of the material in question.
- Pyrolysis phase that has vapors at 650 C to form a reactive monomer of p-xylylene.
- The deposition and polymerization of p-xylylene succeed this to attain Parylene.
The process also requires proper cleaning, activation, and masking the product before placing it inside the deposition chamber. Such product remains at room temperature during the entire process.
Dimer di-p-xylylene is placed in a glass tube at the opposite end of the deposition chamber in an aluminum cup called a boat. The thickness of the coating is determined by the actual volume of the dimer placed in the boat.
Once the process initiates, the end cap is placed on the tube, and the vaporizer radiant heater cycles using a pressure safety interlock to ensure a safe operational limit. Slowly, the dimer takes a vapor state, and the molecules travel down the tube using reduced pressure at the opposite end.
The dimer then moves into the pyrolysis zone, where the high temperature cleaves the dimer into radical monomers. When these molecules enter the deposition chamber, they form a long chain polymer on the surfaces of the chamber. A cold trap is utilized between the deposition chamber and vacuum pump as it prevents the parylene molecules that have not been deposited on the product from getting into the vacuum pump. It prevents oil molecules from back streaming into the chamber. However, the complete process takes place minus a catalyst or solvent.