Silicone (SR) Conformal Coatings

This is a known phenomenon called cobb webbing or spider webbing. Here, the polymer is essentially drying as it’s dispensed resulting in strands. There are a few things you can do to correct this. The first is to lower the pressure of the spray gun. You can also add more solvent to the coating mixture. A third consideration is the relative humidity in the room where application is occurring which ideally is 30-60% R.H.

Applying a single, heavy coat can lead to solvent entrapment and under curing of the film. Here, the surface hardens and entraps solvent within the bulk often leading to a tacky surface. To achieve thicker coats, apply multiple thin coats instead.

Silicone materials hold up well to moisture and most aqueous chemicals like acids and bases. They do not hold up against chemical solvents like alcohols or acetones and are not generally recommended for applications in harsher environments.

These materials are not waterproof. Moisture is still osmosing through the film however, it’s able to osmose out, so the cured film acts like a semi-permeable membrane which is why electronics don’t fail.

There are different tools available to measure the dry film thickness. The easiest is the micrometer where the applicator can simply measure substrate thickness before and after coating with the difference being the dry film thickness. If the underlying substrate is electrically conductive, you can use a Positector which is a non-destructive test method.