Gary cleared most of my question up on this but I realized I may have
left out a part.
Again, using IPC2221 Table 6-1, Electrical Conductor Spacing:
For 300v isolation throughout board (non-conformal coated), std
soldermask coated, the spacings requirements would be:
Pad-pad unmasked (B2 column) = 1.25mm
Trace-trace masked (B4 column) = 0.4mm
Lead-lead termination (A6 column) = 0.8mm

OK so far?
Now, what would the spacings requirement be for unmasked pad to masked
trace? Would it be the same as the B4 column or half way between the B2
and B4 values?

Thanks
Ron

Gary Ferrari wrote:

> Ron,
>
> You are not quite correct in your assumptions. First, the "A" side of
> the table is for component lead terminations, not lands and conductors.
> The lands, as well as conductors, fall on the "B" side of the table.
> That said, the B2 value would be higher than the A6 value since there
> are always traces of contamination on the surface of the board which
> will affect the isolation characteristics. Whereas the component leads
> face air as an insulator and will not see the full effects of surface
> contamination.
>
> Hope this clears it up some.
>
> Regards,
>
>  Gary Ferrari
> Ferrari Technical Services
> 860-350-9300
>
> Ron O wrote:
>
>> Can anyone help interpret the IPC2221 Electrical Conductor Spacing chart
>> 6-1 (pg 39)?
>> I have a pcb requirement of 500V spacing between nets. Board is FR4
>> 2layer, soldermask both sides, no conformal coating. Based on the chart,
>> I need a B4 spacing (0.8mm) for the soldermasked conductors and an A6
>> spacing (1.5mm) for the exposed pad areas (I'm assuming this is pad to
>> pad spacing not pad to coated trace spacing).
>>
>> Is my interpretation correct so far?
>>
>> Next question is the column B2, which applies to uncoated (no SM or
>> conformal) and has a spacing requirement of 2.5mm. So this would be bare
>> trace to bare trace. Why would this spacing need to be greater than bare
>> pad to bare pad (the A6 rating)?
>>
>> ---------------------------------------------------------------------------------
>>
>

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