Conformal coating is a protective coating or polymer film 25-75µm thick (50µm typical) which protect electronic circuits from harsh environments like high humidity, a range of airborne contaminants, moisture, vibration and varying temperatures. By being electrically insulating, it maintains long-term surface insulation resistance (SIR) levels and thus ensures the operational integrity of the assembly.
Humiseal is a pioneer in this field and leaders for over 60 years in array of industries like Aerospace, automotive, Telecoms, Industrial Controls etc.
What Conformal Coating made of?
Conformal coatings are generally made of a polymeric resin and thinned by one or more solvents so that the material can be dispensed easily and it flows properly, when necessary.
Conformal coating are made of different materials like acrylics, urethane, silicone, and epoxy. Every material has its own strength and weaknesses, depending on the required protection and the environment in which the electronic device is located , the best type of resin is chosen. The most common is acrylic which gives high protection from moisture.
Types of Conformal Coatings
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Acrylics conformal coating
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Acrylics is most commonly used conformal coating as it is economical, easy to apply and offer good overall protection. Acrylic coating is known for its high dielectric strength, high moisture/humidity resistance and good abrasion resistance. Acrylics can be easily removed by solvents thus it is most often use with rework and field repair work. Acrylics provides high protection against humidity but not very good with solvents.
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Urethanes conformal coating:
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Urethanes are resistant to chemicals, abrasion and moisture. Due to solvent resistance, they are very difficult to remove. For removing them completely, it has to be soaked for longer time in specialized solvents and has to be whisked with a brush. Urethane conformal coatings are mainly used where salt vapours, noxious gases, fuel vapours, exhaust vapours and chemical exposure are the common concern.
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Silicones conformal coating:
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Silicone conformal coating is good resistant to moisture, salt spray and chemicals. It also provide excellent protection in a wide temperature range. It is rubbery in nature thus it is resilient to vibrational stresses and also usable with reasonable humidity protection like outdoor signage, LED boards etc. Removing a silicone coating is quite tough and it has to be soaked in a specialized solvent for long period of time and agitation from a brush.
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UV curable conformal coating
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UV Curable conformal coatings are resistant to chemicals, moisture ,vibrations and mechanical shocks in electronics devices and PCBs. It is single part coating which cures very fast, has short cycle time and provide faster production speed. It is low in viscosity and thus can be sprayed using selective spray equipment. It is suitable in wide range of applications due to resistance to wide range of solvents and temperature like Aerospace, automotive, staking of PCB components.
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Synthetic rubber conformal coating
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Synthetic Rubber offer superior moisture protection and are extremely flexible. It works very well at high operating temperatures. It has least moisture permeability and increased thermal stability. As the material flexes and recovers under various thermal shocks, it provides great protection to PCB, electronic assemblies and the components under harsh industrial conditions.
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Aerosol conformal coating
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Aerosol are fast drying, clear, solvent based conformal coatings which are typically used to protect PCB and their components.The product has to be applied directly to the substrate which is cleaned thoroughly before coating.The coating thickness should be 25-75 microns and the quality has to be checked using a back light.