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Epoxy Conformal Coating

How Epoxy Protects Surfaces

Epoxy resins (ER), just like any other conformal coating, provides a thin protective film. Coating takes some expertise to apply. If the coating is too thick, problems could include shrinkage, cracking, bubbling or trapped solvent.

Epoxy Benefits

Why Use Epoxy Conformal Coating

Epoxy resins (ER), just like any other conformal coating, provides a thin protective film. Coating takes some expertise to apply. If the coating is too thick, problems could include shrinkage, cracking, bubbling or trapped solvent.

Both systems provide the same benefits. They have good moisture and dielectric resistance. They also have excellent temperature and chemical resistance. Epoxy also has good resistance to abrasion and is rigid.

Epoxy is nearly impossible to rework. Any solvents that can remove Epoxy conformal coating can also remove the epoxy adhering components to Printed Circuit Boards. The solvents also have an affect on the PCB epoxy based laminates. The only possibilities for rework are to either spot remove with a very minimal amount of solvent or burn through the coating with a knife.

Heat cure causes the coating to shrink. A low temp cure or another method is recommended if shrinkage is an issue.

As with Acrylic, Polyurethane and Silicone, Epoxy can be applied by brush, spray or dipping. Spray and machine dipping are most efficient for large batches. Brushing and hand dipping work well for smaller kits. Brushing is recommended for prototypes and assemblies requiring a lot of masking. A buffer should be considered for use with more delicate components.

In comparison to other liquid film materials, epoxy offers exceptional coating strength, dependably resisting abrasion, chemical incursion, humidity and vibration. Unfortunately, this same long-lasting surface durability also makes epoxy coatings very difficult to rework and repair. Epoxy can shrink during polymerization. These two factors make exceptionally careful film application a necessity. Temperature extremes diminish its stress resistance, further limiting epoxy’s use for electronics.

Offered as a single- or two-part compound, epoxy resin (Type ER) conformal coating is defined by extreme hardness; however, that property is also its biggest drawback. Epoxy resin exhibits rugged toughness and durability, allows for ease of application, resists abrasion, humidity, and chemicals, possesses good dielectric and moisture barrier properties and features relatively high glass transition (Tg) temperature.

While epoxies are very good at protection from humidity, chemical and abrasion, they are as stated above very difficult to remove. Below is a brief description of some methods in removing this robust coating:

Thermal
Use extreme caution when burning through epoxy. Though no known gas is emitted, check with the manufacturer before you use this technique.

Mechanical
Because epoxy is so hard, this technique is not recommended. Damage to the board most likely will occur.

Chemical
Complete coating removal for repair is nearly impossible by chemical means (except in the case of hermetically sealed hybrids), as the solvent can’t discriminate between the epoxy coating, the epoxy-glass printed circuit board, and any epoxy-coated or potted components. However, if done carefully, spot removal of the coating may be accomplished by the application with a cotton-tipped swab of a solvent with a methylene chloride base and acid activator.

  • Useful to about 150C [302F]
  • Harder durometer, abrasion resistance
  • CTE closer to epoxy PCB substrate
  • Higher Tg (Glass transition)
  • Good dielectric properties
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