A few days ago someone asked about a thicker conformal coating to cover components left exposed by conventional conformal coating. Thickening a conventional polyurethane conformal coating was proposed.

One part oxygen curing coatings will never cure right and will eventually crack or flake off. It will be extremely difficult to mix a thickener into a one part moisture curing polyurethane conformal coating without pulling a lot of air into the liquid which will result in a lot of bubbles in the coating and possibly premature gelation.

Conap (Cytec) offers a lot of 100% solids, 2 part polyurethane encapsulants. Perhaps a lower viscosity one which will air dry would be suitable for this application if the volume isn't too great.
A customer of mine at HumiSeal had a similar problem with boards indirectly exposed out doors which could get wet in the rain.

Their original solution was to selectively coat the exposed components with a solvent based mastic paste they bought from the hardware store.

I suggested they use a selective silicone encapsulant which they applied with Precision Valve machine by needle (a hypodermic syringe could also be used). The selective encapsulant was much more viscous than a classic conformal coating and left a much thicker coating. The encapsulant was an RTV which cured in the presence of moisture in about an hour.




Edward Mines BEChE, MEChE
238 Willard Dr.
Hewlett, NY  11557
516 205-6523

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