Parylene Conformal Coatings for Oil & Gas Sensors
Posted by Sean Horn
Friday, November 22, 2019 8:00
@ 8:00 AM
Parylene is a transparent polymer offering uniform and pinhole-free conformal coatings. Different varieties of parylene (Parylene N, C, D, AF4, and F) formed by a modification in their molecular structure. Each modification results in a set of material properties that are applicable in different service conditions. The basic type of parylene derivatives is the Parylene N (poly-para-xylylene) monomer.
Parylene offers several advantages for use in the electronics industry and sensors technology. It can penetrate thoroughly to the crevices and voids while coating sharp edges and surfaces, thus provides an excellent sealing for the underlying structures. In sensor technologies, parylene conformal coatings are employed for their insulating, dielectric and/or protective properties. A detailed list of their properties are available in Table and described in the Parylene 101 Guide.
Table: Parylene Types and Properties *Materials data: MatWeb
|Property||Unit||Parylene N||Parylene C||Parylene F-AF4|
|Dielectric constant (@ 1 MHz)||2.66||2.95||2.17|
|Melting point||°C||420||290||≤ 500|
|Durable Heat Resistance||°C||80||100||350|
(@Temperature 25.0 °C)
|Advantage||ü Constant dielectric coefficient at all frequencies
ü High dielectric strength
ü Less wear (low friction coef.)
|ü Low gas permeability
ü High Chemical Resistance
|ü Sub-micron coverage 
ü High thermal resistance
The Parylene Deposition Process:
The chemical vapor deposition (CVD) process of parylene takes place in three steps (sublimation, pyrolysis, deposition). The final coating is formed on the target surface (Elastomer, glass, metal, paper, plastic and, others). To improve the adhesion on the target surface extra care is taken to clean the surface. Subsequently, the samples surfaces are treated using an adhesion promoter such as a silane (A-174). Adhesion promoter forms a monolayer of molecules in a way to provide a high strength bond interface between the surface and the parylene. Samples can be batch processed in a Parylene Vacuum Chamber. The temperature, pressure are set for the ideal coating conditions. The coating process takes place once the parylene powder precursor (Paracyclophanes, dimer) is sublimized and pyrolised forming the monomers. Pyrolysis of the precursor is defined as the thermal decomposition of materials at elevated temperatures in an inert atmosphere and this reaction is irreversible. Afterwards, monomers are deposited as a thin layer in a way to allow for a top layer to grow on them. In the meanwhile, the monomers penetrate to the smallest voids resulting in a uniform, void-free conformal coating. The thickness of the parylene can be controlled and it is decided upon the application area.
Oil & Gas Sensors
Sensors can detect and help in monitoring the dynamic behavior (temperature, pressure, electric current) of a target under different atmospheric conditions (ie. Gaseous, liquid media, temperature, pressure.). The data collected using these sensors contribute to the continuous operation in the oil and gas industry. The data provides important statistics from which shutdowns, risks and emergencies or optimal conditions can be predicted. To allow for a profitable business operation sites must be well maintained and monitored to keep the cash flowing during the high times of the demand. Oil well pressure sensors regulate the liquid levels in the tanks to prevent explosions and, gas sensors help in the detection of a variety of gases such as O2, H2O, CO2, H2S, Methane and others. Unites States O&G exploration and production direct corrosion costs were reported as ≈$1.4 billion annually with $589 million attributed to the surface piping and facility costs, $463 million to downhole tubing expenses, and $320 million to capital expenditures related to corrosion , .
Because, corrosion and harsh environments are a huge concern that entails a high cost in the production and subsequent operations due to the ware of instrumentation the intensely used pipelines and instrumentation requires monitoring by oil and gas sensors. Deep waters offshore, remote arctic locations and reservoirs with unconsolidated sands are the primary sites of exploration. The most challenging sites for use of instrumentation are characterized by the high pressures and high temperatures (HPHT) and the design guidelines for equipment that are used in areas with pressures greater than 15 ksi (103.43 MPa) and temperatures greater than 350 °F (177 °C) (i.e. deep waters 800 – 1800 m) are determined by the American Petroleum Institute , . Looking at this big picture sensors are the essential parts of successful operations in the oil and gas exploration and production industry. These sensors and materials used in their production need to satisfy the durability and thermal stability guidelines among with being able to withstand exposure to a variety of corrosive environments.
Parylene derivatives offer high durability, wear resistance, low friction, low gas and humidity permeability, and relatively high thermal resistance which makes them a favorable candidate for sensor applications either as a protective sealing or as an insulator to be used in the production of sensors. Also, parylene protective coatings can withstand cryogenic and relatively high temperatures (-400 °F (-200 °C) to +400 °F (+200 °C)) while maintaining their electrical and mechanical properties which is a rare property in materials systems. The repeatability, control of the processes and the control of materials behavior under varying conditions in sensor development is important for the integrated electronic circuit’s response. Their high dielectric strength makes them favorable for use as insulators and the dielectric properties can be tuned by modifying their thickness.
Once applied parylene acts as a chemically resistant barrier against gases (O2, N2, CO2, H2 and others), humidity (low permeability), corrosion (high chemical resistance) and provides wear resistance (low coefficient of friction) for a long term (>10 years) under harsh conditions. Parylene C and N are the most commonly used coatings and they can satisfy the needs for temperatures up to ≈100 °C’s under oxidative conditions. Whereas, fluorinated parylenes AF-4 and F can satisfy special conditions with their additional thermal stability at ≈200°C and ≈350 °C, respectively. Using parylene derivatives sensor development and protection of parts that will come into contact with the harsh environments can be satisfied. Parylene is expected to contribute to the development of sensors for challenging HPHT, deep-water, and arctic conditions.
To learn more about parylene, download our parylene 101 whitepaper.
 W. R. Dolbier and W. F. Beach, “Parylene-AF4: a polymer with exceptional dielectric and thermal properties,” J. Fluor. Chem., vol. 122, no. 1, pp. 97–104, Jul. 2003.
 N. Koch, G.H.; Brongers, M.P.; Thompson, N.G.; Virmani, Y.P.; Payer, J.H., “Corrosion Costs and Preventive Strategies In the United States,” p. 12.
 M. Iannuzzi, A. Barnoush, and R. Johnsen, “Materials and corrosion trends in offshore and subsea oil and gas production,” Npj Mater. Degrad., vol. 1, no. 1, pp. 1–11, Jul. 2017.
 P. Bunch, S. Shademan, and A. Bajvani, “Material Characterization Procedure for High Pressure High Temperature Applications Using API 17TR8 Criteria,” presented at the Offshore Technology Conference, 2017.