Tom, 

Foiol thickness is a widely misunderstood number  and based on weight.  If
yoiu look in IPC-MF-140, it wil give you the nominal and tolerances on foil
as received.  If you look in IPC-RB-276 Para 2.9.2.2 and 2.9.2.3., it will
give the numbers after processing.  For example in RB-276, for internal
layers after processing, the minimum for 1 oz. foil is 0.0001 inch.   If 1
oz. is used externally the as plated the minimum is 0.0018 inch.  The common
practice of say on the drawing that the "Copper thickness is 1 oz" is very
misleading and subject to all sorts of interpretations and lawsuits.  Best
practice is to state what copper foil starting thickness is as part of the
material description on the drawing.  If finshed thickness is critical and
does noit fall into numbers in RB-276 it is necessary to put the finished
number on the drawing as a real number.  For example.  "Copper conductor
including foil and plating shall be 0.0002 inches min. thick".  I think that
IPC-D-275 or its replacement to be, IPC2221, will give you some guidelines.

I also agree that copper suppliers an laminate suppliers almost always
provide copper that is 10% below the nominal thickness.  
So, if it is critical, go to RB-276 for minimum thickness after processing.
   
Phil Hinton
Hinton "PWB" Engineering 
[log in to unmask]