EMI / RFI Coatings Overview:
- Commercial electronics are often packaged
within nonmetallic enclosures made from plastics, composites or other nonconductive materials.
Non-conductive enclosures may be processed with conductive coatings to facilitate shielding
for EMC compliance and performance.
EMI RFI coatings and metallizing techniques are available, such as:
vacuum deposition, electroless plating, arc
spray, and conductive spray ‘paint’.
The
most frequently used EMI RFI coatings are a
paint-like mixture of metal particles in an aerosol carrier. Aerosol type
conformal coatings are mixed with very fine conductive particles / material such as silver, nickel,
copper and carbon. Many companies manufacture
highly conductive acrylic and polyurethane
paints filled with silver particles. Surface resistivities
as low as 50 milliohms per square inch are achievable for
a one mil coating thickness. The lower the surface
resistivity of the conductive coating, the greater the
shielding effectiveness. Shielding effectiveness levels
of 60 dB to 100 dB are possible with aerosol type conformal coatings..
Engineering and design should carefully evaluate nonmetallic enclosure coatings for galvanic capatability with connectors, PWB's, and target installation materials.
