The copper foil thickness for one ounce starts at .00135", then it is reduced through normal processing such as cleaning (scrubbing or microetch). So, the practical working thickness of the foil is really something less than one ounce after processing. The number 0.0012 is a good rule of thumb, results may vary.

Doug Smith
Technical Support Engineer
Yamamoto Mfg. (USA), Inc.

(408) 944-8308 (office)
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>>> "<Charles Barker>" <[log in to unmask]@yusa.com> 06/25 7:58 AM >>>
I have a question for all you TechNetters:

If one ounce of copper is .00135" thick (per ANSI/IPC-MF-150F Metal Foil
for Printed Wiring Board), why do the tables in IPC-6012, such as Table
3-9, say: "For each succeeding ounce of copper foil, increase minimum
conductor thickness by 30.0 um (0.0012 inch). My detailitis infected brain
gets hung up on things that don't compute, and this doesn't seem to
compute!