A conformal coating is a specialty polymeric film forming material that protects circuit boards, components and other electronic components from adverse environmental conditions arising from corrosive atmospheres, humidity, heat, fungs and contamination such as dust and dirt.
5 common types of conformal coatings are available. How do you choose the right one for your application?
Acrylic Adhesives can be easily dissolved in many organic solvents and thus make it very easy to have repair work done to the board, and in general provides only selective chemical resistance. Acrylic Adhesive dries rapidly, has good fungus resistance, does not shrink during cure and has good humidity resistance. They suffer from low abrasion resistance, easily leading to scraping, chipping and flaking.
Epoxy, 2 Part
Epoxies are usually 2-part compounds that start curing upon mixing. Epoxy exhibits good abrasive and chemical resistance, as well as reasonable humidity resistance.This coating is difficult to remove and rework. A buffer is recommended around delicate components, since film shrinkage occurs during polymerization. The shrinkage can be minimized by curing at a low temperature.
Polyurethane provides good humidity and chemical resistance. Due to its high chemical resistance, removal of the coating requires the use of stripping agents which may leave ionic residues. These may need to be thoroughly cleaned to prevent corrosion on the underlying board. Polyurethane can be soldered through for rework, but usually results in a brownish residue which affects the appearance of the product.
Silicone is usually a single compound that begins curing upon exposure to moisture in the air, along with temperature. Silicone can provide a good wetting and adhesion of the cured silicone to all surfaces of the electronic device or module. It can be widely used in high temperature (>120C), moisture sensitive, chemical resistant, corrosive, antifungal environments.
Urethane has great strength in protection, hardness and high level of solvent resistance. It provides superb resistance to abrasion and a low level of permeability of moisture. In addition, it has good low temperature adaptability, however it does not perform well in high temperature environments and for the most part cannot be repaired or reworked.