Hi Dave:
> I need a sheet of plastic that goes between a PCB
> and a metal enclosure. This is to make a creepage
> spec. What plastics are good for this? Will
> polycarbonate be suitable and have a 94V-0 rating?
With respect to IEC 60950...
A plastic material used as an electrical
insulator (creepage) has no flame-rating
requirement.
Rather, the material must be a suitable
insulating material. Most plastics are
suitable insulating materials. Check the
UL electrical ratings for your candidate
materials.
If you are seeking UL certification or
equivalent, then the material must be a
UL-recognized plastic.
If the material is within a fire enclosure,
then the material must be V-2 or better.
If it is not within a fire enclosure, then
there is no flame rating requirement.
If you are placing the material between the
PCB and the metal enclosure, then I suspect
you really mean clearance, not creepage. A
creepage is a distance along the surface of
an insulator. If the PCB abuts the metal
enclosure, then it would indeed be a
creepage (as well as a clearance). If the
PCB does not abut the metal enclosure, then
it is a clearance.
This is a very important distinction. If
the clearance does not meet the necessary
distance, and if the metal enclosure is
grounded, then the sheet insulator
comprises Basic Insulation (and there is
no thickness requirement). If the metal
enclosure is not grounded, then the sheet
insulator comprises Reinforced Insulation,
in which case the material thickness must
be 0.4 mm or more.
Good luck, and best regards,
Rich
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