Janice 

Re: Copper thickness designation 
The problem you are reporting is one which is often reported and is easily
corrected.  The final conductor thickness specified as a measurement in
ounces should not be used if the final thickness is critical; the thickness
of copper foil in ounces is kind of a rubbery number and is based on the
average wt. per unit area.  The copper foil supplier typically furnishes a
nominal weight or thickness less 10% and then the fabricator may have
additional processing tolerance depending on what specs he is working to.
 Then you have depth of profile to consider; where do you measure from, peak
or valley. If thickness is critcal, specifiying final copper thickness in
ounces IS NOT THE WAY TO GO.  If your current carrying requirements indicate
that you need 0.0025 inch finished thickness, so specifiy it on the eng. dwg.
and indicate from peak or valley.

The problem that youo mention has come up several times and have been the
subject of several lawsuits. I think the opinions were that ounces is not a
dimensional unit of thickness.  You supposition that 1:0 to 1:2 on the
surface is a 10 year ago rule of thumb and may not be correct for some of the
plating solutiions used today. 

Phil Hinton
[log in to unmask]