Acrylic vs. Polyurethane Conformal Coating

Acrylic resin (Type AR) and polyurethane (Type UR) are widely used conformal coatings. While they share the same methods of applications and end use, consider their individual properties before deciding which conformal coating is the best for an application.

Application Methods

Acrylic liquid conformal coatings, which include MG Chemicals 419C, HumiSeal® 1B31 and HumiSeal 1B73, can be applied in four ways: spray, dip, brush or robotics. The application method may vary depending on the number of products and the complexity of masking requirements. Acrylics are usually applied between .002” and .005” in accordance with IPC-610.

Urethanes like MG Chemicals 4223, HumiSeal 1A33 and HumiSeal 1A20 are applied in the same manner as acrylics. A difference between the two conformal coatings involves cure time. While acrylics typically cure in as little as 30 minutes, most urethanes need more time; some require as much as 30 days. It is advisable to consider total cure times when coating a high-volume application with a tight turnaround.

Common Uses

Acrylics are commonly used to coat printed circuit boards (PCBs) for moisture protection. While also widely used for PCBs, urethanes are primarily used to protect against solvent exposure. Urethanes can also be used for moisture protection and in applications where a more durable, rigid coating is needed.

Disadvantages

In applications with exposure to solvents, acrylics are not always the best solution. Acrylics can be removed with weak solvents such as isopropyl alcohol or xylene so they will not offer the protection needed for mission-critical devices. For products requiring high-temperature applications, acrylics may also present challenges. In the case of HumiSeal 1B31, for example, the max continuous operating temperature is 125ºC. Compare this to silicone conformal coating, whose operating temperature can exceed 200ºC.

Polyurethanes, on the other hand, are difficult to rework. Because urethanes have a high tolerance against solvents, removal of the coating to rework components or even the coating process itself can be lengthy and involve harsh strippers. Often during the removal process, the PCB can become damaged.

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Specialty Coating Systems offers customers regionally-located coating facilities to handle their engineering and production requirements. To discuss the benefits and properties of Parylene conformal coatings and your protection needs with an applications specialist, contact us online or call +1.317.244.1200.