Coating materials have a long and storied history on printed circuit boards. A good conformal coating protects PCB components from moisture, corrosion, contaminants, and other factors such as vibration and thermal shock. Coating materials is a complex science and there is no one best coating or application method for every job. These choices depend on the PCB design, materials used, and assembly. For example, brushing PCB coating materials by hand is a slow, tedious process; however, it is still quite suitable for small batch applications.

       Regardless of which method is chosen, basic application errors can occur, leading to the formation of defects in the coating that ultimately limit the functional life of the PCB.

       The most common problems in the application of coating materials

       The printed circuit board industry is rapidly evolving. Think of all the great technological advances we have seen over the last 30 years! PCBA has evolved at a similar rate. Through this evolution, we have noticed two important trends that lead to potential problems in the application of coating materials. 1.

       1. Components are becoming more complex and are also facing tougher performance requirements

       2. PCBs are shrinking in size, resulting in smaller and more densely placed components.

       The second point makes the application of coating materials very challenging. Due to the small workspace, the properties of the coating material can limit the performance of the PCB: the coating material needs to flow and distribute uniformly across the component, but when the space is small, the surface tension, adhesion and cohesion of the material can prevent the coating material from distributing correctly.

       This is just one of the growing possible challenges. When we looked at the issues that lead to design failures, we noticed three specific pain points. In no particular order, they are:

       1. formation of air bubbles in the coating

       2. too much or too little coating around sharp corners

       3. Defects during extreme heat aging

       These are the three biggest killers of coating material applications. So how do we solve this problem?

       Troubleshooting Common PCB Coating Material Applications

       The short answer is: science - lots of complex, boundary-pushing science. The HumiSeal research team is working tirelessly on the latest breakthroughs in the science of coating materials. This includes redesigning traditional application methods and working to create new coating materials.

       UV-cured coating materials for PCBs

       More and more research is showing promise for UV LED-cured coating materials. Fast-curing coatings are advantageous when dealing with sharp part edges because they cure before the liquid flows to the bottom of the part. As a result, they hold their intended shape well.

       We recommend the use of UV-cured coatings over other fast-curing coatings, such as two-component coatings, because of their relative simplicity and ease of use. Two-component materials usually require specialized mixing equipment and extensive preparation work, and UV-cured coatings have their drawbacks. Due to the limited penetration of ultraviolet (UV) light through the material, they usually need to be applied in multiple layers. However, there is hope that this problem can be solved.

       UVA spectral light waves have a greater penetration range, allowing for thicker coatings and curing. In addition, UVA-cured coatings exhibit increased thermal shock resistance and physical stability. These are not the only new coating materials being developed.

       Sharp Edge Cover Coatings

       One of the latest breakthroughs in coating materials comes in the form of Sharp Edge Cover (SEC). This new coating adheres tightly to sharp component surfaces. This results in a more even distribution of the coating than ever before, reducing the risk of cracks in the material or adhesive not hanging in the corners when it is too thick, and ensuring that every point of the component is fully protected. 

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