Growing up in the Pacific Northwest, there was one thing that every child heard repeatedly from their parents during the fall and winter: “it’s cold outside, go put on a coat!” Coats could be annoying, and would often get forgotten at school or at the park. Coats could also be embarrassing if you had the misfortune of choosing the wrong style or color. But when the rain and snow came, a good heavy coat was the one thing that everyone was glad to have hanging in their closet. There’s nothing better than the warmth, protection, and security from the storm that a good coat can provide.
Circuit boards can also benefit from the protection of a good coat, and in their case, that protection comes from a material called “conformal coating” that is applied to them. Conformal coating is a thin layer of material that protects the board and its components from the environment and from corrosion. Because the material is applied to the board after it is assembled, it “conforms” to the shape of the board and its components. Conformal coating can do a lot to protect a printed circuit board so that it can continue to operate at its peak efficiency. Let’s take a closer look at conformal coating and PCB coating types.
What PCB Coating Types Are and What They are Used For
Conformal coating is a thin film of protective material applied to a circuit board. It can cover the entire board if desired and protects both the board and its parts including the component leads, solder joints, exposed traces, and other areas of exposed metal. This protects the metal from corrosion as well as shielding the entire board from spray, moisture, fungus, dust, and other contaminations from harsh environments. Conformal coating will even help prevent damage from thermal and mechanical stress and even rough handling helping to extend the operational life of the PCB.
Conformal coatings are non-conductive dielectric materials that help to increase the dielectric strength between traces and other metal conductors on the PCB. The increase in dielectric strength reduces the surface area required for circuitry, which allows for more compact and dense PCB layouts. Conformal coatings can be resistant to different types of solvents and chemicals, as well as being heat resistant. And as coating keeps contaminants out, it also helps prevent delicate component leakage and corrosion.
Conformal coating of PCBs is essential for boards that are going to be exposed to harsh environments. As such, you will see conformal coating used in military, aerospace, medical, industrial, automotive, marine, lighting, and energy applications. It used to be that coatings were only applied to military, medical, or other mission-critical PCBs due to the cost. With lower prices, however, conformal coating is becoming more and more common, even in consumer-level products. As conformal coating technologies increase and prices continue to drop, we will see a greater increase in its use.
The Different Types of PCB Conformal Coatings
There are different types of conformal coating materials or chemistries that are used depending on what the specific needs of your PCB are. Here are the more common ones in use:
- Acrylic Resin (AR): These coatings are the most commonly used conformal coatings because they are economical and will protect against a broad range of contamination. They are not the highest level of protection, however, and do not protect against solvents or solvent vapors. They have a very high level of dielectric strength and can be easily removed, making PCB rework very practical.
- Silicone Resin (SR): Silicon coatings have a very wide temperature range of protection and are very chemical, moisture, and salt spray resistant. Due to its rubbery nature, it isn’t abrasion-resistant, but it does hold up very well against vibration stresses. These coatings are often used for environments with high humidity but are difficult to remove and require specialized solvents for PCB rework.
- Urethane Resin (UR): These coatings are excellent at resisting abrasion as well as being moisture and chemical resistant. Because of these qualities, urethane coatings are often used in aerospace applications due to their ability to resist fuel vapors. On the other hand, like silicone, this coating is very difficult to remove and requires specialized solvents for PCB rework.
- Epoxy Resin (ER): Epoxy is somewhat different from the other conformal coatings in that it used to completely encapsulate the electronics in a solid layer of material. This provides excellent protection against humidity, abrasion, and chemical contamination. The hard coating, however, is almost impossible to remove once it is cured.
These conformal coating products are qualified by different industry standards including IPC-CC-830B and IPC-A-610.
Application of Conformal Coating to a Printed Circuit Board
Conformal coating can be applied in different methods. For those boards that are being reworked or repaired, the conformal coating is usually brushed on by the rework technician. While this is a low-cost way to apply coating, it can be very labor-intensive. Another manual method is to spray on the coating with either an aerosol can or a handheld sprayer. Again this is a very labor-intensive operation and is typically used for low production runs. Areas of the board that are not to be coated must be masked off, and you will see variations in the application of the coating due to the nature of it being a manual operation.
For production runs of circuit boards, you will see boards either dipped in their conformal coatings or automatically sprayed. Dipping is often used in high volume runs of boards and will only work if both sides of the board require coating. Automated spraying is done either by running the boards through a conveyor system where reciprocating spray heads apply a consistent coating or by using a selective coating process. Selective coating uses programmable spray nozzles that coat specifically programmed areas of the board.
|Tempo‘s Custom PCB Manufacturing Service
At Tempo Automation, we are ready to work together with you on determining your conformal coating needs for your PCB manufacturing. We have the experience and the resources that you need to make sure that your design is manufactured to the highest levels of quality to ensure that your circuit board will perform to your expectations.
And to help you get started on the best path, we furnish information for your DFM checks and enable you to easily view and download DRC files. If you’re an Altium Designer or Cadence Allegro user, you can simply add these files to your PCB design software. For Mentor Pads or other design packages, we furnish DRC information in other CAD formats and Excel.
If you are ready to have your design manufactured, try our quote tool to upload your CAD and BOM files. If you want more information on various PCB coating types available for your boards, contact us.