In a message dated 2004-04-21 08:36:32 AM Eastern Daylight Time, 
[EMAIL PROTECTED] writes:


> I heard from somewhere it's about 0.0025 Volts per millimeter, but I'm not
> sure under what conditions. 
> 

Are you sure that wasn't per METER? If your units are right, I've got a whole 
lot of designs that violate it! (5V requires 2 meters spacing with that 
number and units)

I recall from a NASA spec years ago using 30V max for 10 mil clearance, and 
that upon further checking, 3V per mil was a good rule of thumb though not 
exactly correct. That's for bare conductors (i.e. exposed through soldermask 
openings) in a normal sea level atmosphere. Containment by a dielectric (even 
soldermask helps some) increases the allowable voltage for any given gap; increase 
in altitude / decrease in air pressure decreases the allowable voltage for a 
given gap.

Steve Hendrix


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