As I was browsing through some previous discussions, I came across the 
following question (yeah, I'm quoting myself). It was regarding the use 
of Figure 3-4 in IPC-D-275 to determine an appropriate trace width based 
on current.

> As an example, say I need 5amps and 20 degrees over ambient is a safe
> assumption. The chart gives ABOUT 100 square mils, which corresponds to
> ABOUT a 75mil trace width on the 1oz copper curve.
> OK, how many of you use 75mils? How safe is this number? 

Many of you responded (THANK YOU) but one issue was never brought up and 
I am still curious about it. 

According to IPC-RB-275 Table 7, a conductor width can be reduced 20% by 
a nick or scratch for a length of 0.5 inches and still be acceptable, 
plating thickness can vary (as well as the 1oz copper stock), traces can 
be over-etched, etc.
 
So does the chart indicate that I should use 75mil aperture in my CAD 
system, or is my goal to take all factors into account and try to ensure 
the END RESULT is 75 mils minimum?  

Am I splitting hairs?						Jack

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