Common Conformal Coating Defects and Solutions
Mallory McGuinness | June 16, 2020
When we say that a chain is only as strong as its weakest link, we aren’t talking about polymer chains – we’re talking about conformal coating defects. Regardless of the type, a single coating defect can affect the long-term reliability of a PCBA or component and must be repaired or removed. This can be costly and labor-intensive.
Therefore, it’s best to avoid defects from occurring in the first place. The following is a list of common defects and how to keep them from cropping up during your conformal coating process.
The 6 Most Common Conformal Coating Defects and Solutions
Capillary flow, also known as scavenging, occurs when a conformal coating migrates from one area of a PCBA to another, leaving behind an inconsistent, uneven finish on the surface.
Common causes for capillary flow include:
- The application of too much coating
- Conformal coating with low viscosity or high surface tension
- Low surface energy of component being coated
To avoid capillary flow from occurring:
- Ensure that the PCBA is entirely clean before coating.
- Use solvent-based coatings in lieu of water-based, and decrease the use of thinners to increase viscosity.
- Prior to coating, heat the board to decrease dry time.
Learn more about epoxy conformal coatings
Cracking and Ripples
Cracking and ripples can compromise a conformal coating film, exposing a substrate or PCBA to potential contaminants.
Common causes for cracks and ripples include:
- Coating that is too thick
- Thermal shock
- Coating that has been cured too quickly
To avoid cracks and ripples:
- Always apply coating at an appropriate thickness.
- Allow for extra drying time at room temperature.
- Consider selecting a coating with a broader effective temperature range.
De-wetting is when a conformal coating will not evenly coat the surface to which it is being applied.
Many things cause dewetting, including:
- An uneven coating application
- Improper mixture of two-part materials
- Residue on the coating surface
- Variations in Surface Tension and Surface Energy
To avoid dewetting, thoroughly clean the material being coated before application.
Learn more about polyurethane conformal coatings
Delamination occurs when a coating has lifted away from the substrate. This hinders protection because the area below the coating is left exposed.
Delamination has many causes, including:
- Too thick of a coating
- Coating not adhering to previous coating layer
- Contamination on coating surface that prevented a good bond to the surface
To prevent delamination:
- Reduce the thickness of the coating.
- Thoroughly clean the substrate before coating.
- Apply a “primer material” that can bond with both the substrate and material used for conformal coating.
A single coating defect can affect the long-term reliability of a PCBA or component.
Orange peel is when a coating appears dull, resembling the skin of an orange.
It is caused by conditions including:
- A substrate that is too hot
- Improper coating mixture or solvent ratio
- Local environment that is too dry during application
- A second coat has been applied before the first coat is dry
To avoid orange peel:
- Apply coating at the specified thickness.
- Reduce the viscosity of the coating.
Learn more about conformal coating vs potting
Air bubbles, Pinholes, and Foam
Bubbles occur when pockets of air get trapped under a conformal coating layer. Foam is an extreme form of bubbling, and sometimes bubbles burst through the conformal coating, forming a pinhole.
Bubbles, pinholes, and foam happen when:
- A coating is too viscous
- The coating is too thick
- Application equipment has not been setup correctly
To avoid air bubbles, pinholes, and foam:
- Use a lower viscosity conformal coating
- Ensure the coating is applied at recommended thickness.
- When applying the coating, do so with thin coats.
Why This Doesn’t Happen at HZO
At HZO, we use a conformal coating application method called chemical vapor deposition (CVD) that circumvents these conformal coating issues. Using CVD, we produce uniform, pinhole-free conformal coatings every time. Contact us today to speak to an expert if you’d like to hear more about our proven technology and processes.
We produce uniform, pinhole-free conformal coatings every time we do a job.
Ryan is a 9-year veteran to the world of protecting electronics from harsh environments and a lover of all things technology.