Parylene Dielectric Properties

Basic Dielectrics and Conformal Coatings

A low dielectric substance is an electrical insulator that becomes polarized by applied energy, reducing the resulting electric field, thus minimizing electric power loss. Conversely, high dielectric mediums are efficient supporters of electrostatic fields that also dissipate thermal energy at a minimal rate; thus, they have the potential to store energy. Dielectric strength, also known as voltage breakdown, and dielectric constant (a relative permittivity ratio), are often assessed during the design of printed-circuit-boards (PCBs) and similar higher-speed electrical components.

The lower the dielectric constant, the less the extent to which a material concentrates electric flux. Composed of weakly bonded molecules, lower dielectric-constant substances such as Parylene conformal coatings produce a reliable barrier between a substrate and its environment. Polarized by electrical charges, they resist electrical conduction and therefore can be effectively used to coat the high-speed electrical components common to IT, biomedical and communications electronics.

Essential Dielectric Properties of the Parylene 

Parylene conformal coatings are known for their documented dielectric properties. Highly corrosion resistant, dense and pinhole free, they provide a completely homogeneous coating surface. Dielectric properties differ according to Parylene type. Table 1 provides a comparison of key electrical properties for the main commercially available variants of Parylene.

Parylene’s Dielectric Performance Relative to Other Conformal Coatings

Parylene’s lower dielectric constants reflect its capacity to withstand intense electrical fields. One of its advantages as a surface coating is an ability to withstand break down when subjected to significant electrical differentials. Competing coatings have higher dielectric constants (epoxy, 3.3 – 4.6, polyurethane, 3.8 – 4.4, silicone, 3.1 – 4.2) and a lower ability to withstand breakdown, i.e. their dielectric strengths are lower (epoxy, 2200, polyurethane, 3500, silicone, 2000), indicative of the diminished ability to provide dielectric protection compared to the Parylenes.

A film’s ability to provide effective electrical protection depends largely on the thickness uniformity of the film. Just one area of inefficient coverage, such as a thin spot or a pin-hole, creates a weak point sufficient to render the entire coating compromised. The gas phase deposition process of the Parylenes eliminates these uniformity concerns, providing reliable properties values that designers can work with at a high level of confidence.

Advanced Applications Aided by Parylene’s Dielectric Properties

Parylene’s dielectric capacities have extended the utility of existing products and aided in the development of new ones. Among current applications are:

• Integrated circuits: Parylene polymers offer comparatively low dielectric constants (k~2.25-3.1), enhancing their utility as coatings for next generation, high frequency and higher-speed integrated circuits and related electronic components. In contrast, conventional dielectrics and metals generate interconnect delays that interfere with sub-.025 µm devices. Parylene’s low k constant enablesproduction of more efficient and reliable high-speed electronics, significantly reducing cross-talk between adjacent lines.
• Radiation applications: Parylene polymers prepared in uniform thicknesses < 0.025 µm exhibit their typical exceptional nonabsorbent and gas barrier properties, when used for radiation generated applications. When used as a conformal coating throughout the entire soft x-ray region, Parylene’s dielectric advantages are apparent in comparison to commercially available Mylar^®, polycarbonate, polypropylene, and similar competitive substances.
• Microchip biomedical labs: Parylene masks have exhibited exceptional and fully biocompatible utility in the development of micropatches of biomolecules within electrowetting-on-dielectric (EWOD) based microfluidic chips used for medical/biological assays and exploration at the cellular level. Full spatial control of the micropatches can be achieved while sustaining the chip’s essential hydrophobicity. The fact that cells can be arranged either singly or as clusters on the chip’s digital microfluidic surface demonstrates Parylene’s capacity to be adapted for additional biomedical purposes.

Conclusion

The outstanding electrical properties of the Parylenes enable designers and developers to achieve superior performance. This is the result of the material’s electrical properties but also due to the inherent uniformity that results from the deposition physics of the vapor deposition polymerization process