What Temperature Will My Parts See During the Parylene Coating Process?

The Parylene coating process involves four steps: drawing vacuum, sublimation, pyrolysis and polymerization. Parts to be coated must be vacuum stable in order to be successfully coated. Sublimation then takes place between 120°C – 175°C wherein the dimerized Parylene precursor is sublimated. Then moving into the pyrolysis section, it undergoes cracking to form the highly reactive monomer molecules. While Pyrolysis takes place at elevated temperatures (above 500°C) in an inert atmosphere, the thermal mass transferred to the chamber is minimal due to low thermal mass of the reactive monomer molecules. Finally, these monomers deposit onto all surfaces within the chamber, forming the long chain polymer known as Parylene.

What temperature is the deposition chamber?

Substrates to be coated are fixtured in the deposition chamber that is typically kept at ambient temperature. Because the process is completed under vacuum, the thermal mass transferred to the chamber is quite low, with chamber temperatures typically remaining within a few degrees of room temperature. Extremely long deposition processes (high Parylene thickness requirements) will result in slightly higher part temperatures. Franz Selbmann et al showed that a slight increase of temperature during the process was possible due to the hot monomer gas [1].

References
[1]    F. Selbmann, M. Baum, M. Wiemer, and T. Gessner, “Deposition of Parylene C and characterization of its hermeticity for the encapsulation of MEMS and medical devices,” in 2016 IEEE 11th Annual International Conference on Nano/Micro Engineered and Molecular Systems (NEMS), Sendai, Japan, Apr. 2016, pp. 427–432, doi: 10.1109/NEMS.2016.7758283.