Removing conformal coating from a circuit board requires matching your method to the type of coating on the board. Acrylic and silicone coatings come off relatively easily with solvents or gentle heat, while urethane coatings resist chemicals and need more aggressive techniques. Epoxy coatings are nearly impossible to remove without damaging the board underneath. Knowing what you’re working with is the single most important step before you start.
Identify the Coating Type First
Conformal coatings fall into four main families, and each one behaves very differently during removal. The industry standard for PCB rework, IPC-7711/7721, lists coating identification as the first procedure in its removal section, rated as an advanced skill. If you skip this step, you risk choosing a method that either won’t work or damages your board.
A UV light is the quickest identification tool. Most acrylic coatings fluoresce brightly under UV, while silicone and urethane coatings may fluoresce weakly or not at all. Epoxy coatings are typically hard and glassy to the touch. If you know the original manufacturer or have access to the board’s build documentation, that’s the most reliable source. When in doubt, test your removal method on a small, non-critical area of the board first.
Solvent Removal for Acrylic and Silicone Coatings
Acrylic conformal coatings dissolve readily in common solvents like isopropyl alcohol or xylene, making them the easiest type to strip chemically. Silicone coatings also have low solvent resistance and respond well to chemical stripping. For both types, the basic process is straightforward: apply the solvent to the coated area, let it dwell for a few minutes, then wipe or brush away the softened coating.
Research on acrylic coating removal found that effective solvents can achieve full substrate exposure within about two to three minutes of dwell time. Solvent blends that are well-matched to the coating chemistry work in roughly three minutes, while poorly matched solvents can take twice as long or more. For spot removal, you can apply solvent with a brush or cotton swab to target a specific component. For full-board stripping, immersion in a solvent bath is faster.
Traditional strippers based on dichloromethane (DCM) work quickly and cheaply, but they carry significant health and environmental concerns. Newer, safer solvent formulations cost up to 30% more than DCM but eliminate the need for extensive protective equipment, hazardous waste handling, and the associated insurance costs. For hobbyists or small shops, that tradeoff usually makes the safer option more practical overall.
Removing Urethane Coatings
Urethane coatings resist moisture, humidity, and harsh chemicals by design, which makes them significantly harder to strip than acrylics or silicones. Standard solvents that dissolve acrylic coatings won’t do much to urethane. You’ll typically need a specialized chemical stripper formulated for urethane, and even then, the process is slower and less predictable.
When chemical methods are too slow, micro-abrasive blasting is the preferred alternative. Start with a general-purpose plastic blasting media, which offers a good balance of speed and control. If the plastic media isn’t cutting through fast enough, you can escalate to walnut shell media, which has more cutting power. With urethane specifically, control your dwell time carefully and avoid dragging debris across exposed solder pads, as this can cause contamination or damage.
Why Epoxy Coatings Are a Special Case
Epoxy conformal coatings are nearly impossible to remove without damaging the board. Their excellent temperature and chemical resistance, the very properties that make them desirable, work against you during rework. Solvents strong enough to dissolve epoxy coatings also tend to dissolve the epoxy adhesives holding the circuit board itself together, which can destroy components and traces.
If you must remove an epoxy coating, your options are limited to thermal methods, careful grinding and scraping, or micro-abrasive blasting. None of these are risk-free. With micro-abrasive blasting, start with plastic media and escalate to walnut shell only if needed. The hard, bonded nature of epoxy coatings can push you toward longer dwell times and higher pressures, which increases the risk of blasting through the solder mask underneath. Use documented limits and inspect frequently.
Thermal Removal Techniques
Heat softens most conformal coatings enough to scrape or peel them away. The general approach is to heat the board to around 150°C, or above the coating’s glass transition temperature (the point where the rigid coating becomes soft and rubbery), then mechanically remove it while it’s still hot.
You have two options for applying heat. Heating the entire board in an oven works for full removal but exposes every component to elevated temperatures. A heat gun or hot-air desoldering tool lets you target a specific area, which is the better choice when the board has heat-sensitive components nearby. Direct the hot air at the zone you want to strip, wait for the coating to soften visibly, then scrape or peel it away before it cools and re-hardens.
Thermal methods work across most coating types but carry the obvious risk of damaging temperature-sensitive parts. Lead-free solder joints on the board can also be affected at higher temperatures, so keep your heat focused and your exposure time short.
Micro-Abrasive Blasting
Micro-abrasive blasting uses a fine stream of particles directed through a small nozzle to erode the coating away. It’s the most versatile mechanical method and works on every coating type, including stubborn urethane and epoxy films. The key variables you control are pressure, nozzle distance, angle, and dwell time. Adjust these parameters first before switching to a harder, more aggressive media.
Three media types cover most situations:
- Polymer media (such as VanAcrylic): The gentlest option. Provides a controllable cut with low risk to solder mask. Best for selective removal on populated boards, fine-pitch areas, and work near component boundaries.
- General plastic media: A middle ground with a broad working range. Stable and predictable once you’ve dialed in your settings. Good for most general conformal coating removal.
- Walnut shell: The most aggressive common option. Greater cutting power for thicker coatings or tougher films, but it can damage fragile solder mask if you’re not careful. Always trial on a test area before committing.
For precision work around individual components, polymer media at low pressure gives you the most control. For clearing larger areas of tough urethane or epoxy coatings, plastic media or walnut shell at moderate pressure will be more efficient.
Manual Scraping and Peeling
The simplest mechanical approach is using a sharp blade, dental pick, or dedicated scraping tool to cut and peel the coating away by hand. This works best on thicker coatings that were applied by dipping or brushing, and on softer formulations like acrylics and silicones that tend to peel in sheets rather than fracturing into fragments. Combining a solvent soak with manual peeling often produces the cleanest results: the solvent loosens the bond while the tool lifts the coating free.
The risk with scraping is obvious. A slip of the blade can sever a trace, scratch through solder mask, or damage a component lead. Work under magnification when possible, and use plastic or wooden tools near sensitive areas to reduce the chance of gouging the board.
Cleaning the Board After Removal
Once the coating is gone, the board isn’t ready for rework or recoating until it’s properly cleaned. Solvent residues, abraded coating particles, and flux left over from the original assembly all act as contaminants that prevent a new coating from bonding properly.
Wipe or wash the stripped area with isopropyl alcohol at 99% purity or higher. For water-based cleaning, rinse with deionized water to avoid introducing new ionic contaminants onto the board. After cleaning, dry the board thoroughly. Applying a new coating over a damp surface traps moisture underneath, which causes bubbles and delamination over time. Even fingerprint oils left during handling can interfere with adhesion, so wear gloves during the final cleaning and recoating steps.
For high-reliability boards in aerospace, medical, or military applications, visual inspection alone isn’t sufficient. Ionic residues invisible to the naked eye can cause dendritic growth between traces, eventually creating short circuits. Cleanliness testing methods like ion chromatography can detect these hidden contaminants before they become field failures.