Homebrew PCBs

--- In Homebrew_PCBs@yahoogroups.com, "lcdpublishing"
<lcdpublishing@...> wrote:
>
> Hi Guys,
> 
> I buy all my PCBs from "Surplus" dealers. Now that I have a bit of 
> collection going AND that some of my designs are getting a bit 
> more "powerful", the weight of copper is getting important.  Does 
> someone know what the thickness of copper is for the different weights?
> 
> Example 1 oz. copper is .001" thick or something similar
> 
> Thanks
> 
> Chris
>
I saw the following on a web site and wanted to follow thru on the
math, so here it is:

Density of copper is 8.94 grams / cc. (cc = cm * cm * cm)
Recall that there are 454 grams per pound (3 places, rounded)

Thickness in um = 
    0.5 * 10000           454
---------------------- * ---- = 17 um
2.54 * 2.54 * 16 * 144   8.94

Some of the numbers used (for reference):
0.5 = ounces/sq-foot (amount of copper)
10000 = um/cm (microns per cm)
2.54 = cm/inch
16 = ounces/pound
144 = square inches/square foot

It boils down to:
oz/sq-ft * 34.16 = micron thickness 
   (applying a 25.4 um/mil conversion)
oz/sq-ft * 1.34 = mills thickness (thousandth of inch)

A calculator program comes in handy to figure this out, along with
some unit analysis to make sure it all fits.

I saw other references, but this "formula" seems to have some basis on
it.  If some of the constants are wrong, feel free to correct them. 
One reference indicates a density of 8.92 grams / cc for copper.

As a side note, sometimes I hear on _This Old House_ (the PBS TV show)
the rain gutter workers refering to 20 oz copper stock.  Turns out
that those guys measure it the same way, so it is probably a copper
industry standard.  I suspect that 1 oz copper wouldn't work in that
application.

Hopefully this will help someone.