Conformal coating process in PCB assembly process is a type of surface finishing with a thin acrylic film applied over the assembled circuit board to protect electronic circuit board from corroding.
Typically applied at thickens of 25-250 μm (micrometers) it is applied to electronic circuitry to act as protection against moisture, dust, chemicals, shock and temperature extremes that, if uncoated (non-protected), could result in damage or failure of the electronics to function.