Conformal coating keeps circuit boards protected
From submarines to the Mt Stromlo observatory, traffic lights to the scoreboard at the MCG, circuitry keeps day-to-day life ticking over smoothly. However, circuit boards are delicate, affected by moisture, salt, chemicals, ranging temperatures, dust, and other contaminants. If left unprotected and uncoated, circuitry can short and 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 provide 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 Australia.
How conformal coatings enhance PCBs
Put quite simply, conformal coating protects the circuit board. 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 conformal coating types – acrylic to PTFE
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 of the use, environment, and expected lifespan of the substrate. There are a range of polymers used for conformal coatings – polyurethane, acrylic, fluoropolymers, silicone, parylene – and each has its advantages or disadvantages. 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. The strippers used to remove it also attack the circuit board itself, so it is nigh on impossible to remove cleanly and without problems. 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 specialised 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 and the best solvent and extreme temperature resistance of the conformal coatings. It also has a high dielectric strength, can form very thin films which completely cover the substrate, and has no curing time.
Disadvantages: Parlylene is applied through chemical vapour deposition in a vacuum chamber, so application requires specialised equipment which is reflected in the 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 to extreme chemical conditions. 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. Polyurethanes are often used for aerospace applications or applications where fuel vapour exposure is an issue.
Disadvantages: It is very difficult to repair and remove, and has a short pot life.
Silicone conformal coating is a flexible option which is also good against high temperatures, moisture, corrosion, chemicals, and thermal shock – they are one of the most popular conformal coating types. 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 methods
The main application processes 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, and the quality requirements of the final coating. The requirements of the electronics themselves also need to be taken into account, such as solvent sensitivity.
- Brushing applies the conformal coating with a brush to specific areas. It is labour intensive and mostly used for repair work or reworking areas.
- 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.
- Aerosol/spray application atomises 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 specialized 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 Australia
Australia has a number of conformal coating specialists and applicators. Below we have collected a list of just a few and the 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. Our quotation service is 100% free, and our experts are here to help. We collaborate with our coating partners to find the right coating solution for your project.
|Conformal Coating Companies||Location||Conformal Coating Types|
|Alfatron||Unit 9 / 36 New Street, Ringwood VIC 3134||Automated selective coating.|
|AT&M||Unit 9, 55 Howe Street, Osborne Park, WA 6017||PCB specialist with conformal coating services|
|ONBoard Solutions||2 Salisbury Street, Botany NSW 2019||Supplier of Humiseal conformal coating products – acrylic, polyurethane, silicone, and UV curable coatings.|
|Petech Pty. Ltd.||Unit 4/15 Bon-Mace Close, Berkeley Vale NSW 2261||Acrylic, urethane, and silicone conformal coating products.|
|Pritchard Electronics||43-45 Orlando Road, Lambton NSW 2299||Applicators of a range of conformal coatings.|