Good point! I agree on the linewidth tolerance issues. How about
        layer counts higher than 10 layers? They get real fun to drill when
        all internals are comprised of HTE copper. 1/2 oz is far more easier
        to drill with all that accumulated copper. As circuit density 
        increases and linewidth decreases, the 1/2 oz copper will be vital
        to hold required critical linewidth tolerances. Like .004".004"         
        (Trace/Space) on dual stripline trying to hit 50 Ohms. 
        (That ones fun! Especially when the material(s) tolerance window 
        gives you basically +/- 6 ohms)

        Groovy
______________________________ Reply Separator _________________________________
Subject: FW: Half ounce internals
Author:  [log in to unmask] 
Date:    2/16/96 8:27 PM


One argument for using is 1/2 oz on internal layers is a reduction in line 
width variation.  There are very few PWB suppliers that can supply supply a 
4 mil line +/-20% on 1oz copper.  In addition, mixed copper thicknesses on a 
layer pair [i.e. lyr 2 (top)and lyr 3 (bottom)] result in reduced yields.  I 
also don't believe there is anyone who can honestly quote a 3 mil line 
+/-20% on 1oz copper and maintain the specification.
     
nwbluez
 ----------
From: TechNet-request
To: Technet
Subject: Half ounce internals
Date: Friday, February 16, 1996 4:40PM
     
A strong consideration for not using 1/2 ounce copper on internal 
layers, is that you only half the width of copper to make a 
connection at the barrel of plating.  Possible problems.  Be careful.
 May not be reliable.
     
Norm Einarson