Conformal Coating

Conformal coating material is applied to electronic circuitry to act as protection against moisture, dust, chemicals, and temperature extremes that, if uncoated (non-protected), could result in damage or failure of the electronics to function. When electronics must withstand harsh environments and added protection is necessary, most circuit board assembly houses coat assemblies with a layer of transparent conformal coating rather than potting.

Precision analog circuitry may suffer degraded accuracy if insulating surfaces become contaminated with ionic substances such as fingerprint residues, which can become weakly conductive in the presence of moisture. (The classic symptom of micro-contamination on an analog circuit board is sudden changes in performance at high humidity, for example when a technician breathes on it). Furthermore, a suitably chosen material coating has proved to actually reduce the effects of mechanical stress and vibrations on the circuit and its ability to cope in extreme temperatures.

For example, in a chip-on-board assembly process, a silicon die is mounted on the board with an adhesive or a soldering process, then electrically connected by wire bonding, typically with .001-inch-diameter gold or aluminum wire. The chip and the wire are very delicate, so they're encapsulated in a version of conformal coating. This prevents accidental contact from damaging the wires or the chip. Another use of conformal coating is to increase the voltage rating of a dense circuit assembly; an insulating coating can withstand a much stronger electric field than air, particularly at high altitude.