Conformal coating protects circuitry from environmental contaminants
Electronics are everywhere in today’s world. From submarines to spacecraft, traffic lights to iPhones, circuitry keeps day-to-day life ticking over smoothly. If left unprotected, moisture, salt, chemicals, ranging temperatures, dust, and other contaminants could cause the circuitry to fail. Keeping circuitry ticking over smoothly is the job of conformal coating. Conformal coating is a thin film coating which protects printed circuit boards (PCBs), components, and electrical devices from harsh or damaging environments and conditions. They do this by providing a dielectric barrier between the circuitry and the atmosphere.
In this article we look at conformal coating, how it works, and the different conformal coating types and their applications. We also list conformal coating applicators and companies in Canada.
Why you need conformal coatings
Conformal coatings protect the circuit board. There are a range of polymers used for conformal coatings – polyurethane, acrylic, fluoropolymers, silicone, parylene – and which one you choose depends on the exact conditions they will need to endure. The transparent polymeric coating is a barrier between the harmful elements of an environment, such as moisture or temperature extremes, while also being breathable enough to let trapped moisture escape. Typical application sectors include automotive, aerospace, military, marine, and even domestic and consumer items like washing machines and phones.
In short, conformal coatings:
- Protect products from heat, moisture, chemicals, and particulates and thus from corrosion and possible short circuits
- Prevent damage from handling, installation, mechanical stresses
- Prolong the lifespan of the PCB, component, or device by eliminating environment-caused degradation
- Only minimally add to the weight of the component due to an application thickness of 25-200µm dependent on the conformal coating types
- ‘Conform’ to the irregularities of the circuit board
- Enable circuitry to get increasingly smaller due to their dielectric properties and insulation
The different types of conformal coating – acrylic to silicone
Conformal coating types vary in their properties and strengths, and which one you choose for your application needs to be carefully matched to the requirements and conditions of the use, environment, and expected lifespan of the substrate. Below we look at the different conformal coating types, their strengths, and their weaknesses, and sum it all up in a handy table.
These are typically one part coatings which dry rapidly and display good temperature range tolerances, good insulation, good durability, and good humidity resistance. They do not shrink as they cure and can be applied to heat-sensitive substrates as they do not give off heat as they cure. Acrylic conformal coating is the easiest applied, easiest repaired, and easiest removed of the conformal coatings, as well as being the most affordable option. Because of this, they are also the most popular of the options.
Disadvantages: Acrylics are not suited for chemical environments and do not have great mechanical strength.
Epoxy conformal coating has good humidity resistance and excellent mechanical strength, chemical resistance, abrasion resistance, moisture resistance, and, like epoxy coatings as a group, generally performs very well in harsh environments.
Disadvantages: Epoxy conformal coating is extremely difficult to remove. This is because the strippers used to remove it would also attack the circuit board itself, so it is nigh on impossible to achieve cleanly. Epoxies also have a short pot life and specific mixing requirements as they are usually two part, and are more prone to surface defects.
- FLUOROPOLYMER (PTFE)
PTFE conformal coating (also known as Teflon) is low-friction as well as being corrosion, heat, and chemical resistant. PTFE also displays dielectric stability.
Disadvantages: PTFE is soft and easily damaged. It requires specialized equipment for application through vapour deposition and is very difficult to repair.
Parylene conformal coating is a thermoplastic coating with a low coefficient of friction, high dielectric strength, can form very thin films with complete coverage, and has no curing time. It has the best solvent and extreme temperature resistance of the conformal coatings.
Disadvantages: Parlylene is applied through chemical vapour deposition in a vacuum chamber, so application requires specialised equipment which is reflected in a higher cost. It is also very difficult to remove, easy to damage, and does not bond as well as the other coatings.
Polyurethane or urethane conformal coatings are best suited for extreme chemical conditions. Polyurethanes are often used for aerospace applications or applications where fuel vapour exposure is an issue. It has excellent chemical resistance, humidity resistance, abrasion resistance, and excellent dielectric properties as well as being suitable across a range of temperatures. It is low in cost and has flexibility in application method.
Disadvantages: It is very difficult to repair and remove, and has a short pot life.
Silicone conformal coating is one of the most popular conformal coating types because they are flexible option which is also good against high temperatures, moisture, corrosion, chemicals, and thermal shock. They are highly adhesive and are used for substrates that will be subject to high temperatures or include components like power resistors.
Disadvantages: Susceptible to abrasion, very difficult to remove, high cost, and, if atomized, it can migrate.
|Conformal Coating Types||Temperature Range||Solvent Resistance||Abrasion Resistance||Electrical Resistance||Ease of Repair|
|FLUOROPOLYMER (PTFE)||Excellent||Excellent||Excellent||Excellent||Very difficult|
Conformal coating application processes
The main application methods for conformal coatings can be divided broadly into manual and automated application. Which you choose will depend on variables such as how much preparation (such as masking or taping) is required, how fast the coating process is, how fast the curing process is, the requirements of the electronics themselves (such as solvent sensitivity), the equipment requirements of the coating, and the quality requirements of the final coating.
- Dip coating is the fastest application method, though it requires a lot of preparation in masking and sealing. In dip coating, the entire circuit board is dipped into a vat of coating material and then allowed to dry. It can be done manually or through an automated process but can only be done with coatings of a lower viscosity such as acrylic.
- Brushing applies the conformal coating with a brush to specific areas. It is labour intensive and mostly used for repair work or reworking areas.
- Aerosol/spray application atomizes the coating and sprays it at the circuit board with air or gas. Can be done manually or by equipment through the selective coating process. All non-deposition coatings can be applied this way.
- Automated selective coating is an aerosol process where certain areas of a circuit board are selected and a programmed machine performs the coating, such as Asymtek. It cuts down on preparation such as masking and guarantees an even, uniform, and repeatable coating. Selective coating can be used with all non-deposition coating types.
- Vapour deposition is the more expensive of the coating processes, as it has more specialised machinery requirements. It vaporises the coating into a mist which then deposits on the circuit board. This is a highly specialized application method used for parylene and PTFE.
Once the coating is applied, the three curing methods are air dry, oven dry, or UV cure.
Where to find conformal coating specialists in Canada
Canada has many companies that provide conformal coating services. These include MIS Electronics Inc and CMC Microsystems. Below is a a list of prominent companies and the conformal coatings services they provide.
If you would like any more information about conformal coatings, get in touch! Simply use the “Request a Quote” button beneath this article and tell us a little about your project to get started. We collaborate with our coating partners to find the right coating for your project. Our quotation service is 100% free, and our experts are here to help.
|Conformal Coating Company||Location||Conformal Coating Types|
|CE3 Electronics Inc||1055 Aviation Ave, Dieppe, NB E1A 9S5||PCB manufacturers that also offers conformal coating services|
|Circuits Central||169 Idema Road, Markham, ON L3R 1A9||UV-cured and air-cured conformal coating applied through automated selective coating|
|CMC Microsystems||945 Princess Street, Suite 103, Kingston, ON K7L 0E9||Parylene coating|
|MIS Electronics Inc.||174 West Beaver Creek Rd, Richmond Hill, ON L4B 1B4||Acrylic, epoxy, urethane, parylene, and silicone coating|
|Selective Conformal Coatings Inc||141 Trade Valley Drive Unit 5, Vaughan, ON L4H 3N6||Conformal coatings applied by selective coating|