Conformal coating is a protective coating or polymer film 25-75µm thick (50µm typical) that ‘conforms’ to the circuit board topology. Its purpose is to protect electronic circuits from harsh environments that may contain high humidity, a range of airborne contaminants and varying temperatures. By being electrically insulating, it maintains long-term surface insulation resistance (SIR) levels and thus ensures the operational integrity of the assembly. It also provides a barrier to air-borne contaminants from the operating environment, such as salt-spray, thus preventing corrosion.

Conformal coatings are a breathable protective layer that will protect against the particular environment the PCA is exposed to by filtering out the airborne contaminants and maintaining long-term surface insulation resistance but will also allow any moisture trapped in the circuit board to escape.

The concept of a conformal coating of electronics was originally proposed and developed through research to meet the demanding requirements of the military decades earlier. HumiSeal was a part of that early research and has remained a pioneer and leader for over 60 years as the technology has expanded to an array of industries today including:

• Aerospace
• Automotive, including Hybrid and EV
• Industrial Controls
• White Goods
• Telecoms
• Energy both Traditional and Renewable

Conformal coatings come in a wide range of forms. From a physical standpoint, conformal coatings are commonly dispersed in organic solvents (solvent-based), dispersed in water (water-based), or supplied in high or 100% solids (silicones and most UV curables).

From a chemical standpoint, conformal coatings’ standard chemistries include acrylics, urethanes, silicones, synthetic rubbers, and UV curable acrylated urethanes. Each chemistry is associated with certain physical properties that are suited for certain conditions and end-uses. For example, silicones tend to have the highest temperature resistance while synthetic rubbers and UV curables often provide the highest level of humidity resistance.

• Insulating properties can allow a reduction in PCB conductor spacing
• Can help eliminate the need for complex, sophisticated enclosures
• Provide extended service life by:
  1. Protecting against humidity, chemical, and physical attack
  2. Protecting against thermal variations and shocks
  3. Protecting against vibration and mechanical shocks

How a conformal coating is applied is dependent mainly upon:

1. Preferred application method
2. Existing Available Equipment (Dip/Spray equipment, curing equipment etc..)
3. Board Design/Complexity/Masking Needs
4. Desired volumes/cycle times.

VIDEO: How to Maximize HumiSeal Aerosol Application Video

VIDEO:How to Hand Spray Conformal Coatings

VIDEO: How and Why to Measure the Surface Energy Before Applying Conformal Coatings

A conformal coating provides resistance to humidity and moisture, but it is not the impermeable barrier one expects with the term waterproof. In fact, Conformal coatings are required to be somewhat permeable to allow entrapped contaminants or outgassing from electronics to escape safely and without damage.

A conformal coating is designed with a relatively high resistance to conduction of electricity. This dielectric performance is relatively unaffected by the presence of liquids (such as water) on the surface of the coating. However, the liquid itself will remain conductive on the surface, and prolonged exposure to standing liquids will eventually degrade the dielectric properties of a conformal coating to some degree due to absorption over time within the coating as well as chemical degradation.

A conformal coating’s protective properties lifespan is highly dependent on the uniformity of application, contaminants both on the electronics and in the environment, and the conditions under which the electronics will be required to perform. In all cases, product performance and service life can be expected to be substantially longer than under the same conditions with no conformal coating protection applied. Factors of 2X to 100X in extended life of product would be considered typical and expected.

With all four application methods noted above, it will also be necessary to dry and in some cases cure or crosslink the applied coating. Not all methods will be applicable or possible for all chemistries, for example UV curing coatings can only be cured with UV curing equipment.

In order to calculate a cost per circuit board (PCB), it is required that you have the following data available:

• Length and Width in Millimeters of PCB (or of coated area if not fully coated)
• Dry thickness of coating in Millimeters (Typically 0.025 to 0.075mm)
• Decimal percent solids of coating (Ex: 35%=0.35, 100%= 1.0)
• Price per liter of your coating

Calculation:

mL/PCB = [width (mm) X length (mm) X dry thickness (mm)/ Decimal % solid] / 1000

Cost per PCB ($/PCB) = [cost ($/L) X Volume per PCB (mL)] / 1000

Example: (L=100mm, W=125mm, Dry Thick=0.075mm, %Solids=40%, Price=$100/Liter)

(100mm x 125mm x 0.075)/ (0.40 x 1000)= 2.34 WET mL per PCB

Cost Per PCB= ($50/Liter x 2.34 mL per PCB)/1000 = $0.12 per PCB