In the electronic equipment manufacturing industry, protecting printed circuit boards (PCBs) from harsh environments is critical. This protection is provided by Conformal Coating, thin, non-conductive films that shield the PCB components, solder joints, and exposed metal areas from environmental damage. These coatings also reinforce the board against thermal, mechanical stress, and rough handling.
The standards that govern conformal coating application provide clear guidelines on how to ensure proper protection for PCBs, covering aspects like chemical composition, application methods, and intended use. As leaders in the field, it’s essential to follow these standards to maintain product reliability and longevity.
Types of Conformal Coatings for PCBs
Conformal coatings come in various types, each tailored to specific requirements:
- Acrylic Resin (AR): Easy to apply and affordable, but with low resistance to chemicals, solvents, and high temperatures. Can be removed with suitable thinner
- Urethane Resin (UR): Offers excellent chemical, humidity, and wear resistance but has long cure times and is difficult to remove.
- Epoxy Resin (ER): Highly resistant to moisture, chemicals, and abrasion, making it ideal for harsh environments. However, it can shrink during curing and is challenging to remove.
- Silicone Resin (SR): Known for its exceptional performance in extreme temperatures and high resistance to humidity and corrosion. However, it is difficult to remove and requires aggressive methods for removal.
- Parylene (XY): Provides superior resistance to extreme temperatures and solvents. It doesn’t require curing and offers high dielectric strength but is difficult to remove and requires specialized equipment for application.
Evolution of Conformal Coating Usage
Historically, conformal coatings were reserved for mission-critical applications such as military, aerospace, automotive, and industrial equipment. As the costs of these coatings have decreased, their use has expanded into consumer electronics, where reliability and longevity are increasingly important.
Standards Governing Conformal Coatings
Several key standards ensure the correct application and performance of conformal coatings:
- IPC-CC-830C: The primary standard for conformal coatings, detailing the qualification process and specifications for materials, curing, viscosity, and electrical properties. It replaced the older MIL-I-46058C standard.
- IPC-A-610G: Defines the acceptability of electronic assemblies, including conformal coating coverage and thickness.
- IPC J-STD-001F: Covers soldered electrical and electronic assemblies, with a focus on the materials and application of conformal coatings.
Additional standards include:
- MIL-I-46058C: Although deactivated for new designs, it is still referenced by some military contractors.
- UL94 and UL746E: Underwriters Laboratory standards that certify the flammability and physical properties of conformal coatings.
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