Six common causes of failure of PCB Conformal Coating

21 june
PCB Conformal Coating is often used in the protection of medical, electronic, protective, aerospace, LED and automotive applications. If the preparation, application and drying processes are not properly managed, then the conformal coating will be problematic, which may endanger the entire coating and then it is the entire product. Fortunately, common conformal coating defects can be avoided.
                         PCB Conformal Coating

Here, we review six common mechanisms that lead to conformal coating failure:

Capillary flow, a common conformal coating defect occurs in capillary action and pushes the coating material away from certain areas to other areas, which can easily lead to inconsistent results. In the best case, the conformal coating is produced unevenly, and in the worst case, the coating will detach, resulting in the substrate being completely exposed. This factor affects the capillary flow of the conformal coating, including the coating being too thin, the coating being too thick, or the surface to be coated being too cold or contaminated, cleaning the surface of the product before application, in the specific application Use the most suitable coating.

Cracking is another failure mechanism of the conformal coating, generally because the temperature during curing and drying is too high, but the cracking of the conformal coating may also be caused by a particularly low temperature and a too thick coating applied. To avoid this, the thermal expansion coefficient can be managed by reducing the thickness of the coating to tightly control the temperature.

Loss of contaminants prevents the conformal coating solution from uniformly adhering the substrate to the "wetting" substrate. Under such problems, some areas of the product remain uncoated, and the exposed substrate is further contaminated and the coating fails. Cleaning is the key to avoiding this conformal coating defect. But the solution – which should be after the problem arises – is to strip the affected area and manually recoat that place through a strict rework process.

Layering, sometimes this happens, the coating process goes well, but the coating does not stick to the board. The proper adhesion of the conformal coating is critical. The corners are easily delaminated because the coating is lifted slightly, leaving not only the unprotected area, but also the coating to further peel off the rolled up mouth. As with most other conformal coating defects, cleaning plays a role in preventing delamination. This failure mechanism, however, may also be caused by the humidity of the particular surface, by the wrong coating material, or by the curing problem.

The orange peel wrinkled, dull conformal coating with a rocky texture appearance is described as a "orange peel" defect. Often, this failure mechanism can occur because the coating is too thick to spread horizontally, or when the spray distance of the coating is too far. It may also be a problem in the curing process. The orange peel wrinkle conformal coating defect can be remedied by spraying at the correct distance, reducing the coating material, fixing the jet air pressure, or adjusting the curing temperature and flow.

Bubbles, pinholes, and foam. If air is trapped in the liquid coating material, conformal coating defects such as bubbles, pinholes, or even foam surfaces may be a product unfortunate. The bubbles may be trapped in the coating material or even the coating is not properly dried. Often, these defects are caused by problems with the coating process, although viscosity and curing temperatures may also play a role.