Conformal coating
Conformal coatings are typically applied with 25–250 μm[1] thickness on electronic circuitry to protect against moisture and other substances.
Many materials can be used as conformal coatings depending on manufacturer needs, such as acrylic, silicone, urethane, and parylene.
More recently, conformal coatings are being used to reduce the formation of whiskers[2] and to prevent current bleed between closely positioned components.
Precision analogue circuitry may suffer degraded accuracy if insulating surfaces become contaminated with ionic substances, such as fingerprint residues, that become mildly conductive in higher humidity.
A suitably chosen material coating can reduce the effects of mechanical stress and vibrations on the circuit and its ability to perform in extreme temperatures.
A coating preserves the performance of electronics primarily by preventing contaminants that can ionize, such as salts, from reaching circuit nodes and combining with water to form a microscopically thin electrolyte film.
The coating is more effective if all surface contamination is removed first, using a highly repeatable industrial process such as vapor degreasing or semi-aqueous washing.
An issue of thin tip coverage, where the material slumps around sharp edges, can be a problem, especially in a condensing atmosphere.
Flow rates and material viscosity are programmed into the computer system, controlling the application so that the desired coating thickness is maintained.
The process quality of dip or dam-and-fill coating and non-atomized spray technology can be improved by applying and then releasing a vacuum while the assembly is submerged in the liquid resin.
For standard solvent-based acrylics, air drying (film formation) is the normal process except where speed is essential.
[6] UV curing of conformal coatings is becoming important for high-volume users in fields such as automotive and consumer electronics.
Another type of coating called parylene is applied with a vacuum deposition process at ambient temperature.
