Parylene coatings conform to MIL-I-46058 Type XY, IPC-CC-830B and USP Class VI, and ISO 10993 approved for use as a medical biocompatible and implantable material.
Parylene is applied at room temperature with specialized vacuum deposition equipment that permits control of the coating rate and thickness.
The deposition process takes place at the molecular level as the chemical, in a dimer form, is first converted into a gas under vacuum and heat; then it is pyrolized to cleave the dimer; and finally the monomer is deposited as a clear polymer film on all exposed surfaces in the deposition chamber.
The single coating builds up one molecule at a time, encapsulating any and all exposed surfaces. The material is applied at rates of 1 to 2 µm per hour. Coating thicknesses from 0.1 to 76 µm can be applied in a single operation.
Parylene will conform to any surface that is stable in a vacuum environment, regardless of the complexity of the geometry.
Parylene is applied in a gaseous state, so there is no risk for bridging, spotting or pooling as can occur with a liquid conformal coating.
For chemical and moisture protection printed circuit boards and medical devices these are typically coated 6 to 25 µm depending on the specific purpose required.
Type N or Natural, has the highest dielectric strength of these two commercial versions, and a dielectric constant value independent of frequency. It is able to penetrate crevices more effectively than type C because of the higher level of molecular activity that occurs during deposition. Parylene N is commonly used where lubricity is most needed and for high frequency electrical applications because of its low dissipation and dielectric constant values.
Parylene C differs chemically from N, having a chlorine atom on the benzene ring that results in a useful combination of electrical and physical properties including particularly low moisture and gas permeability. Parylene C deposits on substrates at a faster rate than Parylene N, and has a lower throw capability and an associated reduction in crevice penetration activity. Parylene C is commonly used for environmental protection.
For applications operating continuously in air temperatures greater than 125°C other variants are available. However, the deposition rates for these higher temperature capability variants are significantly slower than those for Parylene N or C and the cost of application will increase proportionally. For the majority of commercial applications, Parylene N or C will be the logical choice. However, in some cases an alternative variant may be more appropriate. We can advise on the best route on specific projects once the end use requirements are assessed.
Parylene will be exhibiting at the MedTech Ireland Show in Galway on the 25th – 26th September 2019. Come along and meet the team!