> From: Nicholas Lai
> 
> Hello all,
> 
> Is there anyone can answer the following question.
> 
> When we calculate the resistance value of an trace on a PCB Board.
> 
> We use R=£ll/A  where l is the line of trace, A is the coss-section area of
> the
> trace and £lis the presistivity of copper.
> 
> After we measure of the board, the actual resistance value is larger than
> the
> Theorical value around 20% . Why the different is so larger. Do I use the
> wong
> formula?
> Can anyone help on me?
> 
> Best Regard,
> Nicholas Lai
> 10/6/99

Make sure the units you're using for all measurements 
match the units of resistivity for copper you're using.
In other words, if the resistivity you're using is 
in ohm-meters, then you'll have to use meters for 
the area and length of the trace.  If the resistivity 
is in ohm-inches, then area and length will have 
to be in inches.  

Regards, Doug

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