Why We Use Acrylic Conformal Coating on Motor Control Electronics
Motor controllers rarely live in clean, dry, temperature-stable environments. They sit inside pumps, next to motors, in plant rooms, on vehicles and in machinery that sees condensation, dust and vibration every day. In environments such as these exposure to Foreign Objects and Debris (FOD), condensation Conformal coating is one of the simplest ways to protect a PCB from that, and for most of the motor control electronics we design and build, acrylic is our first choice.
Here's why, and when we'd choose something else.
What acrylic coating actually does
Acrylic conformal coatings are solvent-based polymers applied as a thin, clear film over the finished assembly. They follow the shape of the board closely, covering tracks, solder joints and component leads. They cure mainly by solvent evaporation rather than chemical crosslinking, which is what makes them quick to process and easy to remove later.
Protection where it matters
Moisture. Condensation and high humidity cause corrosion, dendritic growth and leakage currents. On a motor controller running at bus voltages well above logic level, a leakage path between power conductors or across a high-impedance sense node can mean erratic control or outright failure. Acrylic gives a good moisture barrier and helps hold insulation resistance where it's needed.
Dust and contamination. Conductive dust and airborne contaminants are a real risk in industrial settings. Gate-drive circuits and switching nodes are particularly sensitive to contamination-driven leakage and noise coupling. Coating seals exposed copper and joints so contamination can't settle directly on them.
This is especially relevant for our pump motor controllers and integrated motor controllers, where the electronics often share an enclosure with fluids, heat and a motor.
Electrical and thermal behaviour
Acrylic has good dielectric strength and adds an extra layer of insulation margin, which helps against surface tracking and arcing in humid conditions. To be clear, it's not a substitute for proper creepage and clearance, and we don't design as if it were. Clearances are designed in from the start as part of our custom motor controller design process; coating is a second line of defence.
Because the film is thin, it has minimal effect on parasitic capacitance, which matters on fast-switching power stages. It also doesn't meaningfully impede heat transfer from MOSFETs, gate drivers or shunt resistors when applied correctly. It isn't a thermal interface material, but it won't undo your thermal design either. It stays flexible through thermal cycling, so it resists cracking and delamination.
Why it suits how we manufacture
As a high-mix, low-volume manufacturer, we need processes that work just as well for a pilot run of 20 as a production batch of 2,000. Acrylic fits that well: it can be sprayed, dipped or selectively applied, and it dries fast without ovens or humidity chambers. That keeps lead times down and production flowing through our contract electronics manufacturing service.
It's inspectable. Acrylic is clear, so solder joints, markings and test points stay visible after coating. That makes post-coat inspection straightforward and supports the traceability and inspection records we keep under our ISO 9001 quality management system, carried out by our IPC-trained staff.
It's reworkable. This is the big one. Acrylic can be removed locally with the right solvent or mechanically, without damaging the board. If a unit comes back for failure analysis, needs a component change for obsolescence, or a design revision has to be applied to stock, we can do it. Epoxies and many polyurethanes make that difficult or impossible, which means scrapping boards that could have been saved.
It's cost-effective. Lower material cost than silicones or specialist urethanes, simple curing and fewer scrapped boards all add up, and those savings go to our customers.
Acrylic coatings are relatively easy to automate and can be applied across the entire board or in specific higher risk areas
When we wouldn't use acrylic
Acrylic covers the majority of the applications we see, but it isn't the answer to everything. Its resistance to aggressive solvents, fuels and prolonged chemical exposure is lower than some alternatives, and it isn't designed for sustained very high temperatures. When an application has a dominant environmental requirement, we'll recommend a different coating and explain the trade-offs, so you can make an informed decision rather than defaulting to whatever's easiest to process.
Polyurethane offers better resistance to chemicals, fuels and solvents, making it a good fit where oils or cleaning agents are present. The trade-off is that it's more difficult to remove for repair.
Epoxy gives a hard, highly chemical-resistant finish, but it's rigid and effectively permanent. We'd only recommend it where serviceability genuinely isn't a consideration.
Parylene for the most demanding applications
For applications that need the highest level of protection, we offer a parylene-coated option. Unlike liquid coatings, parylene is applied by vapour deposition, forming an extremely thin, uniform and pinhole-free film that penetrates under components and into tight gaps that sprays and dips can't reach. It provides an exceptional barrier against moisture, chemicals and corrosive gases, with excellent dielectric properties and negligible impact on weight or dimensions.
That makes parylene well suited to motor controllers exposed to harsh chemicals, continuous immersion risk, high-reliability or safety-critical duty, or where space is so tight that a thicker coating isn't practical. The considerations are cost, the need for careful masking of connectors and test points, and very limited reworkability once applied, so we'll help you decide whether the extra protection justifies those trade-offs for your product.
Working with specialist partners
Where a coating process falls outside what we do in-house, we work with trusted specialist subcontractors to deliver it. Parylene is a good example: it requires dedicated vacuum deposition equipment, so we manage it through an experienced coating partner. The design, masking requirements, logistics and inspection all stay under our control, and the coated assemblies come back into our process for final testing and release under our ISO 9001 quality management system.
For you, that means one point of contact and one accountable supplier, whatever protection your product needs. Coating choice is considered from the earliest stages of our custom motor controller design process and carried through into contract manufacturing, so the protection strategy is designed in rather than bolted on.
Talk to us
Coating choice is part of designing a motor controller properly, not an afterthought. Because we design and manufacture everything in-house in West Yorkshire, we choose the protection strategy alongside the electronics and the enclosure, not separately.
If you're developing a product that needs a robust motor controller, see how our custom motor controller design service works, or read more about Zikodrive and our motor control technology.