Conformal Coating Defects & Issues
Defects in conformal coatings are the same as those encountered when applying any paint. By learning how to apply conformal coating, you can streamline turnaround and avoid issues on the paint line. Below is a summary of the most common coating defects, and how they can be alleviated.
De-Wetting – De-wetting occurs when a coating fails to spread (or wet) over parts of the substrate, and subsequently floods adjacent areas. This happens when common residues such as flux, grease, oil or cutting fluid remain on the surface, impeding the natural flow of the coating and preventing it from spreading out and levelling. The solution is to clean the substrate thoroughly until no contaminants remain.
Orange Peel – As the name implies, “orange peel” results in a bumpy, contoured surface finish that resembles orange peel. This issue stems from the spray technique – namely, setting the spray pressure too low, which provides insufficient atomization, or from using the wrong thinner. Avoid “orange peel” by using the spray settings and thinners recommended in the product’s Technical Data Sheet (TDS).
Bubbled Surface – “Bubbled surface” is caused by three things: 1) Applying the coating with too much pressure, which ingresses air into the liquid coating. 2) Letting the coat dry too quickly, which allows insufficient time for the film to level and deaerate. 3) Applying the coating too thickly, which traps solvent vapors.
To prevent “bubbled surfaces” avoid heavy coats; instead build film thickness by laminating successive thin layers. Refer to MG Chemicals’ Technical Data Sheets for recommended spray settings and dry time-to-handle for each conformal coating product.
Fisheyes – Fisheyes look like small circular lumps with dimples in their centers. They are usually caused by contamination from oil and debris in spray equipment lines. To resolve this issue, simply install a filter that ensures only clean air will be used to spray the coating.
Overspray – Conformal coating overspray occurs when coating is accidentally applied to the wrong area. This can happen when the natural mobility of low-viscosity fluids lets them spread to inappropriate areas (known as “wicking” or capillary action), through operator error, or by uncontrolled wetting of aerosolized liquid coatings. The remedy: do not try to avoid overspray, anticipate it and take preventative measures – namely masking.
Masking involves applying a protective material, such as painter’s tape or peelable latex, to areas where the coating is not wanted. Once the coating has been applied, the masking should be removed quickly, before it dries, to prevent unwanted removal of cured coating.