February 2, 2005

Table 6-1 defines minimum electrical spacing requirements between traces on a PWB.  What is the technical basis for the Table?  Is there a formula associated with the values in the table?  For example, if I have a PWB operating at 30 volts DC, the minimum spacing required between internal traces is 0.05 mm.  What if a PWB operates at 30 VDC but only has 0.04 mm spacing, is there a technical concern?  Based on what formula or technical consideration?

The minimum spacing in the Table are much less than the electric strength requirements for FR4.  For example, my understanding is that FR4 is about 1250 volts/mil.  Therefore, at 1 mil of spacing the PWB should be able to withstand 1250 volts between conductors.

The values in the table are also different than those included in UL 840.  Why?

Any help you can offer on this point would be appreciated.


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