Conformal coatings are very important for PCBs that operate in a harsh environment. Conformal coatings are used on electronics that are near the ocean, outdoors, in aviation, in dusty cities and dirty factories. For example, the PCBs that control gas station pumps and traffic lights are almost always coated to help them endure their harsh environment. Coatings keep water, dust, salt and dirt from touching delicate components and degrading the performance of the boards.
Removing conformal coatings is challenging since they are designed to be very durable and hard to remove. If rework is required, alcohol is not the best choice to remove conformal coatings. While alcohol is inexpensive and widely available, it lacks the solvent “muscle” to dissolve coatings and often requires long soaking times to dissolve the coatings. This is an expensive waste of time and money.
There are four types of conformal coatings: silicone, acrylic, urethane and epoxy. In chemistry, there is a saying that “like dissolves like”. The best way to dissolve any contamination is to use a cleaning fluid with a chemical composition similar to the contamination. So to remove a conformal coating get a cleaning fluid that is chemically similar to the coating itself.
Let’s take a look at some good choices for more common applications:
Dow Silicones Corp and other companies produce very popular conformal coatings based on silicones. They offer great protection while being light, durable and easy to rework. Almost without exception, silicone coatings may be removed by either the VOC-Free Flux Remover — UltraClean™ or the No-Clean Flux Remover – VeriClean™. This product is based on siloxane technologies, so it is chemically very similar to most silicone conformal coatings. In one test with a large Texas computer manufacturer, No-Clean Flux Remover – VeriClean™ removed in two minutes a coating which had been taking 45 minutes to remove with more traditional solvents.
Acrylic coatings, like Humiseal 1B31, can be difficult to remove. Your best choice is the Heavy-Duty Flux Remover – SuprClean™. It is a formidable cleaner with a high Kb value. If it dries a little too quickly for this application, soak the parts in a bath of the solvents. Put a lid on the container so the fluid does not evaporate too quickly.
Urethanes are challenging to remove. Generally, a powerful, slow-drying solvent will work best, if anything works at all. Try the Uncured ExPoxy™ Remover as one option. Usually, these coatings can be removed with a good, long soaking bath in the solvent. Put a cover on the bath to control solvent evaporation.
Epoxy coatings are very difficult to remove because when cured, the molecules “cross-link” to form an unbreakable bond. There is no benchtop-safe chemical which can remove a cured epoxy coating, except physical abrasion which will typically damage the circuit board. If the coating has not cured (hardened) the Uncured ExPoxy™ Remover will be the best option. Usually, these coatings can be removed with a good, long soaking bath in the solvent. Put a cover on the bath to control solvent evaporation.
Paralene is a military-style coating, very thin and rock-hard. It simply cannot be removed chemically.