Protection against dust, moisture, humidity, and other outside elements are essential in the protection of circuit board and components. In order to protect against damage, this article provides methods and means to help assure the components are protected and safely insulated. Below are some methods that can be implemented in assuring the safe coating and removal of components and boards. And we will cover a variety of tops from PCB protective coating thickness, PCB coating removal, and how to cure a PCB conformal coating.
PCB Protective Coating Thickness & Measurement
Thickness:
Thickness depends on the PCB board functions, weight, and profile. We consider many factors when deciding on how thick of an application is needed. A thinly applied coating with result in potential damage to the components as there wouldn’t be enough of a layer to protect against the risks of the environment. Too much? That will add to uneven and frankly unnecessary stress on the solder and other components. The thickness applied to properly coat should fall within the range of 25-250 micrometers and should be applied evenly. Remember, over or under applying the recommended thickness could result in damage.
Dry Measurement:
Only applicable after the coating has dried sufficiently enough or risk of damage will present itself. There are numerous ways to check the PCB coating thickness, however, it is most convenient to deploy the use of calipers. As long as you took a previous measurement of areas you applied the coating too, simply re-measure the same areas after the application of the coating. Averaging the before and after measurements will leave you with the thickness measurement you applied. It seems simple enough.
Wet Measurement:
With a wet film gauge, (which resembles a fine-tooth comb) the thickness of the coating application can be measured while it’s still wet allowing for adjustment as needed prior to drying. The wet film gauge has measurements inscribed, a careful eye is needed to even apply the coating evenly. Once this method is mastered, it’s fairly straight forward and simple.
Either method produces accurate results, it’s a matter of preference which to apply. However, it is recommended to use the Dry Measurement method until you’re comfortable working with and applying the coating. At that point, you can work on mastering the Wet Measurement.
PCB Protective Coating Removal
There are multiple ways to remove the PCB coating, should you need to. Listed below are the top 5 ways to remove PBC. Before applying a particular method, consider the board’s future. If the board is likely to be used again, Scraping is not likely to be your preferred method. If the board or components will have no further use, the method applied is irrelevant.
Parylene
This method is applied using a Chemical Vapor Deposition machine (CVD). This works whether the PCB is applied thick or thinly and is approved by the Food and Drug Administration if applied in a medical atmosphere. Excellent abrasion and chemical resistance along with low thermal expansion make this a good choice for home or hospital settings.
Silicone Resins
Applicable by brush, spray, manually dipped or a machine. This application is perfect for severely hot temperatures, humidity along with being top-notch for corrosion resistance.
Polyurethane Resins
The application of the PCB can be removed with this application where it’s applied thickly or thin. The perfect solution for applications needed to minimize chemical exposure, and it also approved by the Food and Drug Administration. This is usually applied by machine, manually dipped, brushed or sprayed.
Acrylic Resins
One of the best defense against prolonged exposure to moisture. It can be manually dipped, brushed, painted or sprayed and has a glossy coating.
Epoxy Resins
Chip, scratch, and peel resistant. Applies a smooth durable surface and can be applied by manually dipping, spraying, painting, or by machine.
Scraping/Grinding
This method should only be deployed as a last resort. The risk for damage to the components is high implementing this method and should be applied to harder conforming coatings.
All aforementioned methods for PCB coating removal are viable solutions for immediate use.
How to Cure a PCB Conformal Coating
Moisture Cure Coating
The utilization of atmospheric moisture is required to cure in this manner. Humidity plays a vital role in this process, therefore manipulating the humidity can greatly reduce the amount of time needed for the curing process. Conventional, IR ovens and humidifiers are perfect objects than can are capable of accelerating the curing process. Take head, leaving containers unsealed for a prolonged amount of time will cause moisture to be absorbed, facilitating the curing process.
UV Cure Coating
This method utilizes the intensity of ultraviolet light creating a chemical reaction within the coating causing exposed areas to immediately begin the curing process. This method requires a second process of curing, due to the fact it’s impossible for the ultraviolet light to hit every area needed for curation. This application is predominantly used for instant results; its application shouldn’t be left unattended.
Heat Cure / Evaporation Cure Coating
If this method is applied to solvent based conformal coating, the evaporation process will rapidly accelerate simply by applying a heating element. As the liquid evaporates, it leaves behind a coating resin which will need to be removed as well. This method has the potential to alter the coating properties which will cause coating defects if not applied correctly. While heating, the thermal sensitiveness of the components and boards must be accounted for and taking into consideration prior to application.
The curing methods listed above offer the most practiced applications for curing the conformal coating. It is recommended. However, to implement the Moisture and Heating curing method over the UV. Once familiarized with the first 2 methods, you can cautiously proceed to UV.
The above methods are the most well-known applications in reference to PCB. It is recommended to exercise caution and use all safety gear required to reduce the risk of injury.
