During the weather extremes, people apply coverings to their skin to prevent damage; think sunscreen during the summer and moisturizing lotion in the winter. This strategy of using a protective covering is not limited to skin care; it can also help protect electronics. Mission-critical circuit boards operating in extremely stressful and harsh environments have benefited from a protective coating for years. More consumer electronics are now considering applying a conformal coating to their PCBs. Here, we’ll look at conformal coating PCBs and when to consider using them to protect sensitive electronics.
The Purpose of Conformal Coating PCBs
PCB conformal coating is a protective material applied to a fully assembled circuit board, providing a thin transparent covering. The coating is made of non-conductive materials and can cover the entire board and its components, protecting exposed metal areas such as component leads and solder joints. The conformal coating alsogives extra dielectric strength to the circuit board, allowing for reduced spacing between circuits, and will help protect the board against structural and thermal stresses.
Conformal coatings use the following materials, which have different properties:
| Conformal Coating Resins | |
|---|---|
| Acrylic | Acrylics are the easiest conformal coating material to apply and remove and the least expensive. Furthermore, acrylics provide the least protection from abrasion, solvents, and chemicals but have high dielectric strength. |
| Urethane | Urethane has long cure times and is difficult to remove, but it protects against humidity and corrosion. |
| Silicone | This coating protects against high temperatures, humidity, chemicals, and corrosion and adheres well to most PCB materials. However, these capabilities make silicon resins the most difficult to remove, requiring aggressive abrasion and chemical solvents. |
| Epoxy | Epoxy is a difficult conformal coating to remove, but it provides excellent protection against moisture, chemicals, and abrasion. |
Multiple methods exist to apply a conformal coating to a circuit board, starting with manual brushing or spraying. These methods are usually used during rework operations to re-apply the coating or, in the case of spraying, give technicians an economical method to apply it to a new circuit board quickly. Automated spraying machines can also apply conformal coating, with some capable of selective spraying in specific board areas. And lastly, the most common method of applying the conformal coating in a production environment is to dip the boards to cover both sides quickly.
Conformal coatings require a thickness of 25 to 127 microns; in this case, “thicker” does not necessarily equate to “better.” A coating thicker than its specified tolerance does not necessarily offer better protection and usually wastes the material. Thick layers of conformal coating can corrode and fail, especially with cracks or peeling. Curing conformal coating varies depending on the chemistry used and can take hours or days to cure fully. In many cases, it’s possible to accelerate curing with applications of heat or UV. Let’s look next at whether or not your board needs coating.
When Should Printed Circuit Boards Receive Conformal Coating?
Conformal coatings should protect boards subjected to difficult operational conditions. Depending on the type, conformal coatings will help protect the board from thermal stress, abusive or rough handling, and different solvents and chemicals. The conformal coating will also help seal up the potentially delicate components on the board, preventing the possible leakage of their materials and eventual corrosion.
Which coating to use will depend on the circuit board’s application. For instance, acrylics provide only basic protection and do not provide solvent, vapor, or chemical resistance, such as gas or oil pumping equipment. On the other hand, urethane has excellent chemical resistance and is appropriate for aerospace applications where protection against fuel vapors is necessary. The flexible nature of silicone makes it ideal for outdoor applications where protection against vibration is essential. The hard covering provided by epoxy makes it very resistant to moisture and chemicals.
How Your Contract Manufacturer Can Help with PCB Conformal Coating
To get the best protection possible for your circuit board, you need to understand what the board needs protection from and which coating will be the best choice for your application. Remember, PCB rework is crucial when evaluating whether conformal coating PCBs are suitable for manufacturing. If your circuit board is undergoing prototyping during its life cycle, you should avoid using a coating that requires a lot of effort to remove. Digging out the coating material to change the board or even test a circuit takes time and could result in collateral damage that requires even further rework.
The best thing you can do is work with your PCB contract manufacturer to fully understand all the options and considerations that may impact the board. This process is essential and may influence how you lay out your design to lessen the cost of production conformal coating. At VSE, we have been helping our customers with these decisions for a long time, and we know what information you need to build the best board possible.
If you are looking for a CM that prides itself on its care and attention to detail to ensure that each PCB assembly is built to the highest standards, look no further than VSE. Contact us today to learn more about partnering with us for your next project.
