At 11:15 AM 3/9/00 +0000, Mark Holmes wrote:

>I am looking for a table or conversion method that gives copper thickness
>for a given copper weight.

I would expect, without verifying this, that the numbers might depend a bit
on exactly what copper it is. Is it rolled or electrodeposited? What is the
surface roughness?

Anyway, I looked up the density of copper and found a reference at .323
lbs./cubic inch. From this it can be calculated that one ounce of copper
per square foot would average 1.344 mils (milli-inches) thick, which works
out to 34.1 microns (micrometers).

Looking on the web, I found that, typically, the thickness of copper foil
would be described as (for example) 1 oz or 35 microns. Some suppliers gave
a 5 percent tolerance on the 35 micron thickness. An old specification in
Preben Lund gave a thickness and tolerance value for 1 oz copper of 35
microns +10/-5 microns.

Anyway, 35 microns is 1.378 mils, thus the common reference to 1.4 mils as
the thickness of one ounce copper foil.

Johnson and Graham give the thickness of 1 oz. copper as 1.35 mils, without
giving a reference. If I were entering formulas into an impedance or signal
integrity calculator, I'd tend to use this value. Of course, one needs also
to add the thickness of copper plating, if any, additional to the foil....

Other variables probably swamp the variability or imprecision in the foil
thickness in determining impedance, such as width variation due to etch
imprecision, variations in the dielectric constant of the core or prepreg
material, plating thickness variation, etc. Nominal 1 oz plating is often
specified as 1 mil minimum thickness, though it would be 1.4 mils nominal.



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