TYPICAL CHARACTERISTICS OF VARIOUS CURED COATING MATERIALS

Properties Acrylics Urethane Epoxy Silicone
Volume resistivity, ohm/cm (50% RH, 23°C) 2 x 1015
Volume resistivity, ohm/cm (50% RH, 23°C) 1015 11 x 1014 1012 – 1012 2 – 1015
Dielectric constant, 60 cycles 3 – 4 5.4 – 7.6 3.5 – 5.0 2.7 – 3.1
Dielectric constant, 103 cycles 2.5 – 3.5 5.5 – 7.6 3.5 – 4.5
Dielectric constant, 106 cycles 2.2 – 3.2 4.2 – 5.1 3.3 – 4.0 2.6 – 2.7
Dissipation (power) factor, 60 cycles .02 – .04 .015 – .048 .002 – 2.7 .001 – .007
Dissipation (power) factor, 103 cycles .02 – .04 .043 – .060 .002 – .02
Dissipation (power) factor, 106 cycles 2.5 – 3.5 .05 – .07 .03 – .05 .001 – .002
Thermal conductivity, 10.4 cal/sec/dq.cm/1°C/CM 3 – 6 1.7 – 7.4 4 – 5 3.5 – 7.5
Thermal expansion 10.5/°C 5 – 9 10 – 20 4.5 – 6.5 > 25
Resistance to heat (°F) continuous 250 250 250 400
Effect of weak acids None Slight dissolve None Little to None
Effect of weak alkalis None Slight dissolve None Little to None
Effect of organic solvents Attached by ketones,
armoatics, & chlorinated solvents
Resists most Generally resistant Attacked by some

 

COATING THICKNESS

Under the IPC–CC-830, MIL-I-46058 and IPC-A-610 guidelines, recommended conformal coating thickness has been defined as follows:

Type of Coating Thickness in inches Thickness in mm
Acrylic 0.00118 – 0.00512 0.03 – 0.13
Polyurethane or Urethane 0.00118 – 0.00512 0.03 – 0.13
Epoxy 0.00118 – 0.00512 0.03 – 0.13
Silicone 0.00197 – 0.00827 0.05 – 0.21