How to Remove Conformal Coating from PCB？
Are you working on a PCB repair but can’t make any progress due to the conformal coating? Conformal coatings help protect PCBs from moisture, dust, and other contaminants. But when it is time for repairs, these coatings also act as an obstacle and need to be removed.
Removing conformal coating from a printed circuit board (PCB) can be tricky if you don’t understand the process involved. There are various methods that can be used but they all require special equipment and chemicals that may not be readily accessible outside of professional electronics shops.
If you need to remove conformal coating from your PCBs, there are some steps you can take to ensure its successful removal without damaging the board or shorting out components. In this article, we will explain how to safely remove the protective layer of conformal coating in no time at all.
Table of Contents
Why Is Conformal Coating Removed?
You may need to remove the protective coating on a PCB for a variety of reasons, such as:
- Repairs
- Upgrades
- Modifications
- Testing
- Contamination
- New coating
The removal of the conformal coating is occasionally necessary for repairs and reworking of the PCB. Removing the conformal coating provides access to the areas where you need to work.
You may also need to remove the conformal coating before completing upgrades or modifications. Adding or removing components or modifying the circuit may require the removal of the coating.
Recoating the PCB may be necessary due to contamination. Spills and buildup from environmental factors, such as smoke, may be difficult to remove without stripping the conformal coating from the PCB.
Along with the reasons discussed, you may decide to give a PCB a new coating due to a variety of other factors. However, adding a new coating often requires the removal of the existing one. The new coating may not be compatible with the old one.
Types of Conformal Coating
Conformal coatings are thin layers of film applied to printed circuit boards (PCBs) to protect against dust, interference, and damage. PCB Manufacturers offer a variety of materials for coating PCBs. The main categories of conformal coating include:
Urethanz
Urethane conformal coatings typically provide increased durability compared to other options. They also have good resistance to humidity but are often difficult to remove and require a longer cure time.
Acrylate urethane and polyurethane are sub-categories of urethane-based coatings that offer a shorter cure time. These coatings cure quickly under UV light, making them popular among hobbyists.
Acrylic
Acrylic coatings can dry at room temperature without UV light. They are also easy to remove but less suitable for use in high temperatures or harsh environments.
Acrylic conformal coatings are made with a combination of polymers and solvents. When the solvents dry, the acrylic coating dries, creating a protective layer on the PCB.
Silicone
Silicone coatings are flexible and adhere easily to most components. A silicone coating also has good resistance to humidity, corrosion, and chemicals. However, it is one of the most difficult coatings to remove.
Epoxy
Epoxy-based conformal coatings are also difficult to remove but provide great chemical resistance and work well in harsh environments.
How to Identify Which Conformal Coating Is on the PCB
You need to identify the type of conformal coating on the PCB before attempting to remove it. Some of the removal methods may not work with certain types of coatings. There are several ways to identify the type of conformal coating:
Visual inspection
You can visually inspect the PCB for the characteristics associated with specific types of coatings. Epoxy, acrylic, and urethane coatings are often glossy. Silicone has a semi-gloss surface with a rubbery texture.
The transparency of the coating may also help determine the type of coating and the best removal method. Thinner, more transparent coatings are often easily removed with chemical solvents. These types of coatings are often made with acrylic or urethane materials.
Opaque coatings are often thicker and more likely to be made from silicone or epoxy. Chemical solvents are less likely to work well on these types of coatings.
Using a Label
Inspect the PCB for any labels or markings that may indicate the type of conformal coating on the board. Some manufacturers include the name of the coating material.
Using Material Testing
Material testing can help identify the type of coating when the PCB does not include a label. Use a chemical solvent designed to dissolve specific materials.
If you suspect that the PCB has an acrylic-based coating, try using butyrolactone. This solvent is commonly used as a conformal coating remover. Other types of coatings typically require a harsher solvent for removal.
Instead of using a chemical solvent, you can also test the hardness of the material. Abrasive removal techniques, such as scraping and grinding, tend to work best with hard coatings. Soft coatings are often easily removed with brushing techniques.
How to Remove Specific Types of Conformal Coating
Choosing the best removal method depends on the type of conformal coating you want to remove:
- Acrylic – chemical solvent and thermal method
- Urethane – chemical solvent, thermal method, or grinding
- Epoxy – peeling, thermal method, or grinding
- Silicone – chemical solvent, peeling, or grinding
No matter the method, you should first remove the PCB from its housing and disconnect any peripheral components.
Chemical Solvent Method
Chemical solvents are used to dissolve the coating without harming the components or circuit. This method tends to work best with acrylic, silicone, and urethane coatings, as epoxy is difficult to dissolve.
Toluene and xylene are commonly used as chemical solvents for removing conformal coatings. Both types of solvents are strong enough to eat away most types of coatings other than epoxy coatings.
You can also purchase conformal coating remover products. These products are specially formulated to remove most types of coatings.
Using a chemical solvent requires placing the PCB in a container and allowing it to soak. Depending on the solvent, the PCB may need to soak for 10 to 15 minutes.
Chemical solvents can also be used to treat isolated areas. If you do not want to remove the conformal coating entirely, you may apply the solvent to a smaller area isolated from the rest of the board using a solder mask.
After using the solvent, the board is soaked or rinsed using a PCB cleaner. These steps should be completed in an area with good ventilation, as the use of chemicals to dissolve conformal coatings could produce harmful fumes. Some solvents are also flammable.
Along with good ventilation, using a chemical solvent requires personal protection equipment (PPE). Wear safety glasses or goggles and solvent-resistant gloves. A small wire brush may also be necessary for scrubbing areas of the board.
Peeling Method
The peeling method is best suited for dealing with thick silicone-based conformal coatings. However, peeling the conformal layer from the board could also damage components or the board itself.
Try to peel a portion of the silicone coating using tweezers or a dull knife. If the coating does not lift easily, it may need to soak in a chemical solvent to loosen the bond. Soak the PCB in a solvent for 10 to 15 minutes before rinsing it with a cleanser.
Use tweezers or a dull knife and carefully peel back the silicone coating. Heating a dull knife or the tip of a pair of tweezers may help with the removal of the coating.
Thermal Method
The thermal method works on all types of conformal coatings other than silicone-based coatings. As with the peeling method, the thermal method may damage sensitive components. It involves the use of heat to carefully melt the coating.
Adequate ventilation is also necessary due to the harmful fumes produced when melting the conformal coating. Work in small sections at a time and avoid applying heat for too long, as consistent exposure to heat increases the risk of damage to other components and leads.
Scraping, peeling, and solvents may also be necessary when using the thermal method to remove coatings. After melting the coating, residue and portions of the coating may remain, requiring one of the other methods for complete removal.
The thermal method is not the most efficient option for removing the coating from an entire board but may work well when targeting a specific area. You can focus on an isolated area to remove or add components.
Grinding and Scraping Method
Grinding and scraping can remove almost any type of coating, making it a suitable option for some of the thicker coating materials, such as epoxy and silicone.
Grinding and scraping also create risk, as you may generate electrostatic energy, which could damage components.
Scrape away the coating using the end of a scraping tool, such as a utility knife. You can also try grinding away the coating using a grinding accessory attached to a power drill. Both methods require caution to avoid accidentally scraping or grinding nearby components.
Summary
Conformal coatings protect printed circuit boards (PCBs) but can get in the way of rework and repairs. Before working on a PCB, you may need to remove the conformal coating for access to the components and circuits.
The best conformal coating removal method depends on the type of material used. Common options include acrylic, urethane, epoxy, and silicone-based coatings. Removal methods include chemical solvents, peeling, thermal removal, and grinding or scraping.
Thin coatings, such as acrylic, are often easily dissolved with a chemical solvent. Thicker coatings, such as silicone and epoxy, are easier to remove with grinding, scraping, or peeling. In some cases, a chemical solvent may be needed to help loosen silicone coatings.
Safety equipment is also necessary to protect from the fumes generated during the removal of conformal coatings. Always wear protective gloves and glasses and work in a well-ventilated space.
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