Latest / Hardware Startups with Fexingo: Devices, Robotics, and Manufacturing Tech Companies / How Hardware Startups Use Conformal Coating for Circuit Protection
Transcript
- Lucas: So you design a circuit board, it works perfectly on the bench. Then you ship a hundred units to customers in Florida or Singapore, and three months later a dozen come back dead. You open them up and see corrosion crusted across the pins, maybe a little blackened resistor. That's the moment you learn about conformal coating. Luna: I've heard the term, but I think most hardware founders don't really think about it until they get that callback. What is it exactly? Lucas: It's a thin polymer film — typically 25 to 75 microns thick — applied over the assembled circuit board. It seals the components and solder joints from moisture, dust, chemicals, and vibration. Think of it as a raincoat for your electronics. It's not potting, which is a thick epoxy that fully encapsulates. Conformal coating just follows the contours of the board. Luna: Okay, so it's a layer that breathes a little, but keeps liquid out. What are the main types? Lucas: Three workhorse chemistries. Acrylic — easy to apply, easy to remove for rework, decent moisture resistance. Urethane — tougher, more chemical resistant, but harder to rework. And silicone — handles extreme temperatures, flexible, great for high-vibration environments, but it's soft and can be messy to apply. There's also parylene, which is vapor-deposited and gives the best protection, but it's expensive and requires vacuum chamber equipment. Luna: Which one do you see most often in hardware startups? Lucas: Acrylic by far. It's forgiving. You can brush it on, spray it on, or dip the board. And if you need to replace a component, you can dissolve the coating with a solvent and reapply. For a startup iterating quickly, that's huge. Urethane and silicone lock you in more. Lucas: I was talking to a founder last month who makes outdoor sensors — soil moisture probes for agriculture. They were using no coating at all, just relying on the IP65 enclosure. But condensation formed inside the enclosure during temperature swings. They lost about 12 percent of field units in the first year. Switched to a simple acrylic conformal coating, failure rate dropped below 1 percent. Cost increase per board was maybe 50 cents. Luna: Fifty cents per board versus a 12 percent field failure rate — that math is almost too easy. So why don't more hardware startups do it from day one? Lucas: Two reasons. First, they don't know it exists until they have a problem. Second, they're worried about rework. If you coat a board and then find a bug in firmware or a bad solder joint, you have to strip the coating, fix it, and recoat. That adds time and risk. But honestly, if you design for test and keep a few uncoated units for debugging, it's manageable. Luna: And there's a thermal consideration too, right? Coating can trap heat. Lucas: Yeah, that's the real gotcha. Conformal coating is an insulator. If you have power components that rely on airflow, coating them can raise their junction temperature by 10 to 20 degrees Celsius. You have to be smart about it — either mask off high-heat components like MOSFETs and voltage regulators, or use a silicone coating that handles higher temps. Some startups do selective coating with a robot, spraying only the areas that need protection. Lucas: Look, if today's episode was worth a coffee to you, that's the link — buy me a coffee dot com slash fexingo. The smallest gesture keeps this show ad-free and focused on what actually matters for builders. Luna: Totally agree. We don't do sponsors, we don't do ads — just listener support. And it genuinely makes a difference. Lucas: Exactly. So back to coating — let's talk about application methods, because how you apply it matters almost as much as what you apply. Lucas: At prototype stage, most startups use aerosol spray cans. You can get a can of acrylic conformal coating for about 15 dollars. You mask off connectors, switches, and any components that shouldn't be coated — like the edge connector on a memory card slot — then spray from about 8 inches away. It's fast, but inconsistent. You can get runs, thin spots, or overspray. Luna: And you have to let it cure. How long does that take? Lucas: Acrylic dries to the touch in about 10 minutes, fully cures in 24 hours. Urethane and silicone take longer. Some startups skip the cure time by using uv curable coatings — you apply it, hit it with UV light, and it's cured in seconds. But those are more expensive and require UV equipment. Luna: When do you move from spray cans to something more automated? Lucas: Once you're doing more than a few hundred boards a month, spray cans become labor-intensive and inconsistent. That's when you look at selective coating robots. They use a programmable dispense valve to spray coating precisely where you want it. You can define keep-out zones in software, so no masking is needed. A system like that starts around 30 to 50 thousand dollars, but contract manufacturers can do it for you per board. Luna: So you could outsource it until you hit scale. That makes sense. What about inspection? How do you verify the coating is good? Lucas: You can do a visual check under UV light — most coatings have a fluorescent tracer that glows under UV, so you can see coverage. For thickness, you use a magnetic gauge or an eddy current probe. Some advanced systems use laser profilometry. But honestly, for most startups, a UV light and a trained pair of eyes catches 90 percent of defects. Lucas: One more thing — if your device is going into an extreme environment, like underwater or high-pressure washdown, conformal coating alone might not be enough. You might need to combine it with potting or a full hermetic seal. But for 90 percent of consumer and industrial electronics, a 50-micron layer of acrylic is all you need. Luna: What's a good rule of thumb for a hardware founder deciding whether to coat? Lucas: If your device operates in an environment where the relative humidity exceeds 80 percent for more than a few hours a day, or if it sees thermal cycling that could cause condensation, you should coat it. Also, if your product will be handled by humans — think wearables, medical devices, handheld tools — the oils and sweat from skin can corrode boards over time. Coating is cheap insurance. Luna: And don't forget the cost of field failures. One recall can wipe out your margin for an entire production run. Lucas: Exactly. I've seen startups burn through their entire seed round just handling RMAs from corrosion failures. A 50-cent coating would have saved them. So my advice: include conformal coating in your BOM from the start, even if you don't apply it until later. It's one of those things that's easy to add early and painful to retrofit. Luna: Good point. And if you're prototyping, just use the spray can. It's low commitment. Lucas: Right. And when you move to production, find a CM that does selective coating. You'll get consistent quality without the masking headache. Luna: Alright, that's a solid practical takeaway. Thanks Lucas. Lucas: Cheers Luna. Next episode we'll talk about something every hardware startup eventually needs: how to set up a basic reliability test lab.