Parylene vs Acrylic Conformal Coatings

Parylene and acrylic resins serve as conformal coatings, yet their similarities are limited. Due to their distinct properties, each possesses unique uses and capabilities.

Application

Acrylic conformal coatings, a type of liquid conformal coating, can be applied in four ways: by spray, dip, brush or robotics. The chosen method depends on several factors, such as the quantity of products, the complexity of masking requirements and the skill level of operators. Typically, these coatings are applied at thicknesses ranging from 0.002” to 0.005”.

Parylene coating is applied using a vapor deposition process. The deposition rates for Parylene typically range around 0.2 mils per hour, resulting in coating times from 1 to over 24 hours depending on the type and thickness needed. The process starts with the raw dimer in a solid state placed into a loading boat, then inserted into a vaporizer. The dimer is heated to between 100ºC-150ºC, where it vaporizes and undergoes sublimation, splitting into a monomer. This monomer gas is drawn onto the substrate one molecule at a time within the coating chamber at ambient temperatures. The final step is the cold trap, chilled to -90ºC to -120ºC, which captures any remaining Parylene materials. This application process differs significantly from traditional wet chemistry coatings like acrylics. Parylene films are typically applied between 0.0005” and 0.002” but can be as thin as 0.0001”.

Common Uses

Acrylics are widely employed in electronics for their affordability, easy application and resistance to moisture and chemicals. In the realm of printed circuit boards (PCBs), acrylics act as a protective coating guarding against moisture that could harm the fragile electronic components.

Parylene, known for its application on printed circuit boards, is widely utilized in medical products like stents, catheters and needles due to its biocompatibility and durability. Beyond healthcare and electronics, Parylene finds utility in aerospace and automotive sectors, serving as a protective coating for vital components such as sensors, connectors, and wires in high-stress environments.

Overall, while both acrylics and Parylene have their specific uses, they both play important roles in various industries due to their protective capabilities. Choosing the right material depends on the specific application and its requirements.

Drawbacks

When dealing with solvent exposure, acrylic conformal coating may not provide optimal protection. While it can be removed using mild solvents like isopropyl alcohol or xylene, it falls short when faced with stronger solvents. This lack of resilience can be especially concerning for critical devices.

Acrylic coatings may not meet the demands of high-temperature applications. Take, for instance, HumiSeal® 1B31, a widely used acrylic coating with a maximum continuous operating temperature of 125ºC. In contrast, silicone conformal coatings can withstand temperatures exceeding 200ºC.

One drawback of Parylene lies in its cost, often exceeding that of alternative conformal coatings. This higher expense can be attributed to various factors including the intricacies of the process, the quality of raw materials, and the labor-intensive preparation required prior to coating. While exceptions exist, in general, when comparing an item priced with Parylene against one using wet chemistry, the former tends to command a premium.

A significant challenge faced by many of our high-volume manufacturers is the restricted throughput of Parylene. Runs on the Parylene machine can last anywhere between eight to twenty-four hours. Due to the confined chamber space, only a set amount of product can be processed in each coating cycle. This, combined with the substantial capital investment required for new equipment, can significantly disrupt both our internal and our customers’ delivery timelines.

Conclusion

In conclusion, while acrylic and Parylene conformal coatings offer distinct advantages and limitations, they each find crucial applications in diverse industries. The choice between the two materials hinges on specific needs and environmental demands. Acrylics excel in electronics for their cost-effectiveness and moisture resistance, whereas Parylene is commonly used in healthcare, aerospace, and automotive sectors due to its biocompatibility and durability. Understanding the unique properties and drawbacks of each coating is essential for selecting the most suitable option for specific applications.