To protect a circuit board and some of the other components on an electronic device you’re designing and manufacturing, you can apply conformal coatings. These are thin, polymeric film-forming products which can provide your electronics with basic protection from a loose piece of metal can help hold down the components, and may add other useful features.
You can use them to provide excellent protection from corrosion, heat, fungus, humidity and simple airborne contaminants like dust or dirt. These coatings can also increase dielectric resistance. Overall, they boost the operational integrity of your design.
Why are they called “conformal” coatings? While there are several types of conformal coatings to choose from, all “conform” to the irregularities of a printed circuit board. Choosing the right coating is a complex decision involving the application of your design, the timeline for manufacturing, and local and national regulations.
There are several types of traditional conformal coatings, which are resin-based and semi-permeable, which means they are not fully waterproof. There are also non-traditional coatings you can apply to printed circuit boards (PCBs) which may provide waterproofing but come with disadvantages such as inflexibility or difficulty to remove.
The traditional conformal coatings include:
- Acrylic resin: A basic option, acrylic resin provides basic protection including abrasions and moisture. The only area they provide excellent protection is in dielectric strength. Otherwise, they are a low-cost option you may choose if you need a conformal coating which is simple to remove.
- Silicone resin: Silicone coatings are highly flexible, but this comes with the downside of not providing much abrasion resistance but providing relief from vibration stresses. It is also an excellent option in a wide range of temperatures and moist or high-humidity environments (including salt spray.) Some formulations of silicone can coat LEDs. It is challenging to remove all silicone coatings.
- Urethane resin: This is a wise coating to choose when you have combined concerns of abrasion, chemicals, and moisture. Urethane provides excellent protection, but fully removing it is a challenge.
Non-traditional coatings you may consider include:
- Thin film
How do you choose between coatings? Sometimes it takes professional support to maximize the type of protection your circuit board will need while working within a budget and under regulations. The team at MIS Electronics can offer you more information about all of these coating types. Speak to us about a design readiness review meeting.
Conformal Coating Process
Application and curing are the two basic steps in the process of coating your PCBs, but you may also add removal depending on your needs. For application, you have several options, including:
- Spraying: You can apply your coating through both manual and automatic spraying processes, with different spray applicators. When done manually, it can be time-consuming, and you may find the quality of the boards is inconsistent. However, automatic spraying corrects these issues and is less time-consuming.
- Selective: For high-volume applications, it is best to use computer-guided selective spraying, which does not require masking in many circumstances. It can also be more easily integrated with curing methods.
- Dipping: Placing the board into a container of the solution and waiting for a specified time will coat the board. Speed of immersion and withdrawal is also important. And, of course, both sides of the board will be coated with this method, which is not always ideal. You can protect components from coating with masking.
- Brushing: Brushing is almost exclusively used for prototypes, repair and rework as it is challenging to perform well and consistently.
For curing, you also have several options, including:
- Evaporative curing: For resins, the liquid evaporates over time and the rest of the coating cures. You do not have to rely solely on evaporative curing but may combine it with another type. This may be important to speed up the process, which can take days to fully cure (although the boards may be handled in an hour or so.)
- Moisture curing: The coating reacts with the moisture in the air to cure. The moisture may even be provided by the carrier solvents. While these PCBs may be handled in an hour, they will still take days to cure fully. Many silicone and urethane coatings offer moisture curing.
- Heat curing: Often used as a secondary curing method, heat can make your PCB coating cure faster.
- UV curing: The fastest cure option, if your coating is UV cure compatible, you can use UV light to almost immediately cure it. Of course, areas that are shadowed may take longer.
How do you choose between application methods? There are a number of factors to consider. You should consider:
- How fast you need your boards coated, and how soon they need to be handled after coating.
- Your design requirements and if any components are sensitive to solvents.
- Whether other components will need to be masked or taped for protection before coating.
- What equipment you may need to perform coating, and if you have the room for it.
- How much automation your coating process should include, as automation can make for reliability and repeatability.
It’s great to have professional support while you make these decisions. The team at MIS Electronics can help with all of your manufacturing decisions, including inspection for accuracy, defects, electrostatic damage and more. We track our stock in real-time so that we know we can complete our scheduled production runs.
What about when you need to remove a conformal coating? There are a few methods you may be able to select depending on the type and characteristics of your coating, including:
- Thermal exposure
- Grinding or scraping
Achieving the best coating results is important for the viability and reliability of your PCB. We can help you make the best decisions for your specific application, timeline, and design. We also offer shipping and delivery. Speak to the experts at MIS for a no-obligation quote.