Regardless of the variant, Parylene in general garners a great deal of praise for the many advantages it offers as a protective conformal coating for applications as varied as medical, aerospace, defense, LEDs, and automotive. Chief among the coating’s benefits, however, is that it can withstand common sterilization techniques, such as electron beam (e-beam), gamma, ethylene oxide (EtO), and autoclave.
Like many chemicals, para-xylylene actually comes in several common variants:
- N. The most basic type of the compound is highly elastic and, as such, is very good at penetrating small areas on components.
- C. The C variant of the chemical replaces one aromatic hydrogen component with a chlorine atom. It is less elastic and is extremely popular in medical applications, in part due to its high degree of moisture resistance.
While Parylene has a very high melting point -- from 290 to 420 degrees Celsius, depending on the variant -- it suffers thermal stress at much lower temperatures, especially when it is heated in the presence of oxygen. While it can last 10 years at 220 degrees Celsius in a vacuum, its temperature handling capabilities go down to 100 degrees when exposed to oxygen. The C variant reaches it’sT5 point at just 125 degrees Celsius. This is lower than the temperature used in many autoclaves for sterilization. Furthermore, Parylene C has shown annealing when sterilized by high-temperature steam and had increased crystallinity.
Parylene is somewhat of an anomaly when it comes to radiation sterilization. Although radiation sterilization methods such as e-beam and gamma are extremely common, they can compromise the integrity of certain materials, particularly polymeric thin films. “Thin part sections, thin films, and fibers present in a component or product can allow for excessive oxygen exposure during the irradiation process, thus causing degradation of the polymer material,” according to sterilization specialist Sterigenics.
Despite its status as a thin polymer film, however, Parylene is prized for its ability to withstand radiation sterilization methods, unlike many of its fellow films. Parylene C, which, as mentioned, is frequently employed in medical applications, generally maintains its chemical structure under radiation sterilization via e-beam or gamma methods. Although it may yellow slightly after radiation, the coating is so thin that such a slight discoloration is likely to not be visually detectable.
Contact Diamond-MT for help choosing the variant and for a free quote for your next project.