What are the primary functions of conformal coating?

The primary function of conformal coating is to prevent the electronic circuit boards from long-term corrosions due to moisture condensation.

Other desirable features include a better prevention of electrical shorts in high humidity days.

If I have protected my electronics in a sealed plastic or metal box but the electronics are used outdoor, do I still need to conformal coat my circuit boards inside the sealed box?

Having a sealed electrical box is good for rain. Moisture can still pass through the plastic boxes and rubber gasket.

Sealed boxes do not “breathe” and thus trapped moisture that cannot escape and will condense to become sitting water inside the box at night or colder weather. Condensed with potentially contaminating ionics from the air is one of the most potent corrosive ingredient.

How thick should the conformal coatings be for optimum protections?

Per IPC-A-610 Traditional conformal coatings such as polyurethane, acrylic and silicone should be;

Acrylic/Urethanes .00118 - .00512 mils
Silicones .00197 - .00827 mils
Xy (Parylene) .00039 - .00197 mils

Is there an advantages offered by conformal coating that are physically stronger and harder?

Conformal coating is not designed as physical protection media.

General mechanical strength is not required. As long as the conformal coating remains intact at low and high temperature, low and high humidity, resists water and common chemical and solvent, they will be effective conformal coating.

What are dielectric strength and its relevance in conformal coating?

Dielectric strength is a measurement of insulation strength of the coating. Generally higher the better.

However, the circuit boards are supposedly designed to have adequate protection against normal operation. As long as the conformal coating do not negatively affect the dielectric strength in air, they generally will be adequate.

What are the different methods of applying conformal coatings and their relative advantages and disadvantages?

Brush coating is used for smaller volume production. It has the advantage of applying conformal coating only on those needed areas. Labor with such method is higher.

Spray coating is used for larger volume production and generally faster. However, areas that must not be coated must be properly masked before coating.

Dip coating is used for those requirements that need complete coverage. Extensive masking is required because the boards will be fully submerged. This method is costly.

How do I mask the areas of circuit boards that cannot be coated over with conformal coating?

Typical masking method is taping with dots, high temp tapes, boots, and liquid latex mask.

Who do we call when we need an outside source to coat or pot our boards?

Specialized Coating Services - 510-226-8700.

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