How Contamination Affects Conformal Coating

The presence of contamination can severely affect the conformal coating process and cause defects due to:

1. High surface energy/Poor wettability of the surface

Contamination from flux residues, process oils, mold release and fingerprints disrupts adhesion and causes “dewetting”, where the liquid coating backs away, or delamination, where the cured coating peels away from the surface

2. Moisture Buildup

Flux residue left on the PCB absorbs moisture present in the air and increases the chances of electrochemical migration

3. Uneven coating application

Residue left on the PCB results in an uneven surface for coating; oily spots or silicone particles create small, crater-like openings known as fish eyes in the conformal coating; the coating and any residue can also interact chemically, which can increase the likelihood of defects like bubbles.

Read more about the types of conformal coating defects here

Defects from conformal coating can severely affect the production process or even cause malfunctions in the final product. Therefore, it is vital to ensure that the board is clean even before the conformal coating is applied.