A conformal-coated PCB has a protective layer that makes it more reliable. The layer keeps away contaminants and provides insulation to prevent electrical leakage. Find out more about the PCB and its benefits below.
What is Conformal Coating on PCB?
In electronics manufacturing, conformal coating refers to a polymeric membrane applied to finished circuit assemblies. This layer is remarkably thin, typically ranging from 25 to 250 microns.
It encapsulates the entire assembly, with the exception of critical areas that must remain bare for connectivity, such as sockets, connectors, interface pads, and test points.
These films are indispensable for boards operating in challenging conditions where exposure to dust, moisture, and corrosive chemicals is likely.
Conformal Coating Purpose and Benefits
Not all circuit boards operate in mild conditions. Some do so in challenging environments. Coating them serves these two main functions: environmental protection and electrical insulation.
Environmental Protection
Some conditions, such as outdoor and industrial applications, expose circuit boards to a range of conditions. Examples include corrosive chemicals, water or moisture, dust, salts, and more.
Coating the boards with a protective film shields them from environmental damage. It not only makes the boards reliable in such conditions but also prolongs their life.
Electrical Insulation
Apart from manufacturing defects, a PCB can experience short circuits if conductive contaminants land on its surface. Corrosion can also cause it, usually due to moisture damage or adverse chemical reactions.
Applying a conformal film helps prevent the problem. The film is a dielectric and highly insulating. Its thickness determines the protection level, with thicker layers being more effective on high-current boards.
Resource: https://www.researchgate.net
Types of Conformal Coating Materials
Conformal coating materials are typically polymers. They include silicone, acrylic, polyurethane, epoxy, and parylene. Let’s examine the properties and the best applications of each.
Silicone (SR)
Silicone is flexible and highly moisture-resistant. It also offers excellent resistance to extreme temperatures. On the downside, it doesn’t resist chemical damage as well. It’s also difficult to remove.
The material’s resistance to vibration and outdoor conditions makes it suitable for harsh applications. It has the best uses in PCBs for automotive, military, and aerospace applications.
Acrylic (AR)
Acrylic is one of the most popular materials due to its ease of application and cost-effectiveness. Acrylic resins are also easier to remove using solvents, enabling repair and rework.
The material offers good moisture resistance but has moderate protection against heat and chemicals. It is well-suited for general-purpose electronics or PCBs for mild environments.
Polyurethane (PU/UR)
This polymer has excellent flexibility for high-vibration uses. Another advantage is its ability to withstand chemicals, wide temperature ranges, and abrasives.
These qualities make the material suitable for most industrial circuit boards. You can also choose it for automotive boards and similar applications.
Epoxy (ER)
Epoxy sets into a rigid film that offers superb chemical resistance. However, the rigidity makes it prone to cracking, limiting its application scope.
Suitable uses for epoxy-coated boards include marine electronics, where chemical resistance is a crucial requirement. The polymer also suits defense PCBs and automotive systems.
Parylene (XY)
Parylene forms an extremely thin, even layer. The coating thickness can be around 0.0005 to 0.002 inches. Its advantages include offering superior coverage and protection against moisture and chemicals.
It has a complex application method (vacuum deposition) that requires specialized equipment. This requirement makes it more expensive than other choices.
The polymer suits critical circuit boards where reliability is paramount. Examples are medical, defense, and aerospace electronics.
Resource: https://www.youtube.com/watch?v=d8rHLhW5LYI
Conformal Coating Application Methods
The film has various application methods. The technique to use depends on various factors, such as polymer type and production volume. Application options include brushing, dipping, spraying, and vapor deposition.
Brushing
It involves applying the film by hand with a brush. Although slow and laborious, it’s a cost-effective method that suits small batches, including prototyping and rework.
Dip Coating
The entire circuit board is immersed in a tank of coating resin. This method ensures complete coverage and material efficiency (no overspray). However, it requires extensive masking of connectors and sensitive areas to prevent the coating from entering places it shouldn’t, which can be labor-intensive.
Spraying
Spraying can be manual (using an aerosol can or nozzle) or automated, depending on the number of boards. Automated spraying reduces costs in high-volume production runs.
Vapor Deposition
Chemical vapor deposition uses specialized equipment and technologies to apply the coating. It has the advantage of ensuring a thin, uniform polymeric film across the entire board.
Resource: https://www.youtube.com/watch?v=APBmFtRgpnI
How to Choose Conformal Coating
Different conformal film materials are available, as discussed earlier. Each resin has advantages, disadvantages, and best applications. Consider these factors when selecting the polymer type.
Application Conditions
Harsher environments demand materials with superior qualities, while milder ones can use those with moderate characteristics. Base your selection on the PCB’s operating conditions.
Electrical Requirements
High insulation prevents electrical problems. Choose a polymer whose dielectric properties match the circuit board’s current and voltage levels or signal quality needs.
Process Compatibility
Base your selection on the required application and curing method. That means aligning the choice with the production volume, estimated costs, and other factors. For instance, choose acrylic if you need a cost-effective solution that is easy to apply and rework.
Repair Needs
Will the board require frequent repair or rework? Choose a polymer that is easy to strip when you need to repair the board. A good example is acrylic, which is also cheaper than most other resins.
Budget and Cost
Ensure the coating material cost is within your project’s budget without compromising the required protection. For instance, parylene offers good qualities but is too expensive for general-purpose boards.
Conformal Coating PCB Applications
A conformal-coated PCB withstands harsh operating conditions. Its application environments are usually those that expose it to outdoor conditions. These layers form a barrier that prevents damage and performance issues.
The environment type determines the kind of resin the PCB uses. Some, such as silicone, offer better heat and vibration resistance. On the other hand, an epoxy coating will resist abrasion better.
Applications that require coated PCBs span the entire electronics industry. They include the following: Consumer electronics, industrial systems, automotive, medical, telecommunications, military, and aerospace.
Conclusion
A conformal coating circuit board has a protective polymer layer. The layer ensures reliable performance and longevity in tough applications. Different materials offer varying levels of protection, making proper selection crucial.
At Jamindo, we manufacture your PCB to suit the application environment, whether mild or harsh. Our engineers can guide you on the best protection method for guaranteed long-term reliability. Contact us now to learn more about our services.
