Definition
Author
- Dr Lee Hitchens, Nexus
De-wetting is the tendency of the coating material to refuse to wet the surface that it has been applied to evenly.
The effect tends to act locally due to local contamination.
It can be a global affect right across the board.
Download our PDF guide Solving conformal coating problems in the application process now.
Examples of conformal coating de-wetting
Examples are shown in the images where the conformal coating has de-wetting, potentially providing inadequate coating protection to the board surface.
Causes of de-wetting in conformal coating
Factors that influence de-wetting usually involve non-ionic contamination such as:
- Residues from board manufacture including silicone surfactants from solder resist & HASL rinse contamination
- Component residues like mould-release agents
- Silicone oil from adhesives in production
- Soldering processes
- Cleaning bath contamination where rinsing has failed
- Operator handling adding contaminants
How to prevent de-wetting in conformal coating
It is possible to minimise conformal coating de-wetting effects by three processes:
- Control the process: Minimise the contaminants that are on the component parts before assembly. This includes laminate & component cleanliness control before assembly and selection of low residue process materials including fluxes and pastes.
- Clean the boards: Cleanliness of the boards before conformal coating will minimise de-wetting defects.
- Repair while processing: After applying the coating, locally strip the de-wetted area and re-apply the coating to the correct specification.
Download our PDF guide Solving conformal coating problems in the application process now.
Links
| Blistering | Blushing | Bubble | Contamination |
| Capillary Flow | Corrosion | Cracking | Delamination |
| De-wetting | Discolouration | Fish Eyes | Layering |
| Mealing | Orange Peel | Shadowing | Uneven coating |