Polyurethane coatings are amongst one of the most popular choices for conformal coating applications, they are available as single component, two component, UV curable, and water borne systems. Download the Urethane Resin 101 Guide today to learn more about this popular coating!
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Comparing Coating Solutions
Conformal Coating Types
There are 5 types of conformal coating. Acrylic Resin (AR), Epoxy Resin (ER), Polyurethane (UR) and Silicone (SR) are the liquids. Para-xylylene, or more commonly known as Parylene, is the fifth type. Each has advantages and disadvantages. All provide adequate to excellent moisture/humidity resistance and all are RoHS compliant. The following comparison is to be used as informational only. Please contact us for assistance on deciding what will suit your needs best.
Acrylic is a single compound that is a good fungus barrier, easy, dries to the touch and cures quickly, can be soldered through without emitting odor, does not shrink, had decent temperature range (-55 to +130 C) and has a long pot life. The biggest drawback with acrylic is its high chemical sensitivity but that makes rework ability easier.
Epoxy’s are a good chemical and abrasion resistor. However, they are nearly impossible to repair. Any stripper used to remove the coating would also attack the epoxy potted components and the epoxy-glass printed circuit boards.
Polyurethanes are the best at moisture barriers as it holds up very well for extended periods. UR’s are good chemical resistors and are easy to apply. They are available in multiple systems, one part, two part, UV curable and water base. UR’s have longer cure times and are difficult to repair.
Silicones hold up well in extreme temperatures of up to 200C. They do not contain solvents and have very little odor. Silicones have good UV resistance and adhere well to PCB’s. Silicones have limited solvent resistance, are harder to apply, rework ability is challenging and is expensive.
Parylene has the highest cost, no rework ability and the most critical application process of all the conformal coatings. However, it is across the board one of the best conformal coating options. Parylene truly conforms without pin-holes or bubbles. It is flexible and excellent abrasion resistor a good chemical, temperature and dielectric barrier. The most consistent and thinnest coverage is possible with Parylene and is the only coating approved by the FDA to be applied to medical devices.
Here is how Urethane conformal coating compares with other types:
|Ease of Rework||Easy||Moderate||Near impossible||Easy||Difficult|