The Next Stage of Total PCB Protection: Sharp Edge Conformal Coatings
Modern PCBs are smaller and more densely populated with sensitive components than ever before, especially in demanding industries such as automotive and aerospace. Conventional application methods generally involve spraying or dipping to spread conformal coatings as evenly as they can manage, but the process is not without limitations.
Current spray and manual brushing applications are limited in their ability to apply even thickness across an uneven surface by the processes of fluid dynamics and flow. As a result, below is a general depiction of a typical conformal coating distribution showing thin areas on and around vertical surfaces and thicker areas in areas prone to accumulation.
Spray and manual applications can only be applied so fine, even when handled by automation. As a result, this is a general depiction of conformal coating distribution.
So what’s the problem?
1.When coatings are applied too thin, these areas do not get sufficient protection, leaving these corners at risk of corrosion and electrical failure.
2.When coatings are applied too thick, the material risks cracking as too much coating fails to set properly, enhancing risk of cracks and exposing areas to various environmental conditions.
This problem is not new, and many industries fail to notice issues at all. This distribution pattern works, but can it work better?
Why Do Conformal Coatings Set Unevenly?
There are a few reasons for this, and it isn’t just because of sprayer heads. Let’s look at a few reasons why the spread isn’t perfectly uniform:
Viscosity on Uneven Surfaces
Lower solids and lower viscosity coatings will tend to flow off vertical surfaces more readily and solidify slower. This can lead to very even thickness on horizontal regions but an uneven spread on vertical sides. This is the result of natural fluid dynamics.
Carrier Solvent Volatility
Most conformal coatings are carried and dissolved in industrial solvents or water. The volatility of the carrier fluids can affect thickness and uniformity. Slower evaporating fluids will slow drying and solidification and lead to more flow off vertical components. Fast-evaporating solvents can help avoid excess flow but can lead to skinning or “orange peel” thickness variations on flat areas, as well as bubbles forming on the base of components where higher coating thickness is accumulated.
Surface Energy of the PCB and Components
Surface energy is a measurement of any surface or material’s ability to pull a liquid to form an even coating layer. Generally, higher values of surface energy result in better and more even wetting of the coating. The ideal situation for coating uniformity is high surface energy of the solid. It is common that plastic surfaces of PCB components will have low or inadequate surface energy due to mold release or plasticizing agents covering their surface. This often leads to poor wetting on the tops and corners of components.
Introducing Sharp Edge Coatings from HumiSeal
The scientists at HumiSeal have developed a new type of conformal coating material. This formulation is designed to adhere along the edges and sides of components better than ever before. This is the new Sharp Edge Coatings. While Sharp Edge Coatings are still early in their developmental life cycle, current testing has yielded significant improvements over traditional conformal coating applications.
Link:https://blog.humiseal.com/sharp-edge-solutions
