Fluoropolymer process

Co-authors and contributors

  • Dr Lee Hitchens, Nexus

There are two methods for applying fluoropolymer coatings to circuit boards. Nexus explores both.
There are several variations of ultra thin fluoropolymer coatings that are applied through different application methods.

Two of the most popular methods of applications are:

(a) immersing (dipping) the product in a liquid which dries onto the substrate, and

(b) Partial vacuum deposition where the coating is deposited onto the surface in a gaseous state.

We can take a look at both methods in a little more detail.

Liquid immersion (dipping)

Typically, for liquid application, these fluorochemical polymer coatings are suspended in an organic solvent such as a Hydrofluoroether (HFE).

They are non-flammable, generally low toxicity and not VOCs (Volatile Organic Compounds).

Their concentration is in the region of 1-2% solids.

The surface modifier can be spray, dipped or brushed.

But, the preferred method is dipping since one of the most important advantages highlighted by the manufacturers of these coatings is that in general you don’t need to mask the components.

So, the material is held in a dip tank of some description, the substrate is immersed quickly into the liquid, withdrawn from the tank, and the coating dries extremely quickly, leaving the board coated.

It is a very simple process.

Partial vacuum veposition

For the alternative method, the technique is slightly more complex. Again, different methods apply here but in general they follow similar lines of process. That is:

  1. The substrates are loaded into a chamber
  2. The pressure is lowered on the system
  3. The surface of the substrate is plasma cleaned to create free radical sites (very clean areas) on the surface
  4. The monomer (coating before it joins together) is released as a gas into the chamber
  5. The monomer forms covalent bonds with the free radical sites as the coating loves to stick to clean sites
  6. The coating polymerises (the small monomers join together to make very long molecules called polymers) and forms the hydrophobic layer
  7. The chamber is brought back to room temperature and the substrate is coated.

There seems to be more steps here but since the process is automated it is a very straightforward process.

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