In a message dated 8/13/2002, you write:
> To me, it's sort of funny in that it just says that the Creepage and > Clearance distances do not apply on inner layers of void free PCBs. > That's nice; but I can't find where a distance is specified. I mean, I > would think that there should be some minimum distance between an AC line > and a 5V SELV line on an inner layer of the board!!!! > > Our layout guy has a military specification that specifies insulation for > 300-500V circuits. It specifies .100" on external layers and .010" on > internal layers...which would work out to a factor of 10 reduction between > surface layers and inner layers Hi Chris: I work with EN 60950, not EN 61010-1, so my comments here are only general. In EN 60950 the creepage and clearance requirements can be eliminated for inner layers, but all other requirements for the relevant insulation still apply. For example, both supplementary insulation and reinforced insulation still require a minimum of 0.4 mm through solid insulation. Also, any relevant hipot tests for the insulation in question still apply. In general, a well constructed circuit board will have extraordinary insulation between traces on the same layer, due to the high dielectric strength of the prepreg and the bonding agents that are used. Even a separation .002" will, in theory, have a dielectric strength of more than 1000 volts. However, I prefer to be cautious here, in the event that a defect creates a small air gap in the isolation area. I would suggest using as large a gap as you can reasonably achieve, even if the regulations call out no minimum or a minimum of only 0.4 mm. The 0.8 mm target that you have nominated sounds OK to me, but if you can bump it up to 1.0 mm or more, that would be nice. Joe Randolph Telecom Design Consultant Randolph Telecom, Inc. 781-721-2848 http://www.randolph-telecom.com
