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28:16 1996 |
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"Jeff Seeger" <simon.ipc.org!bort.mv.net!rapidcad!jseeger> |
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Gary,
The 1 oz for 2 oz swap can be less than totally safe.
The major differences, thickness and power handling, can manifest
themselves in a couple of ways.
If a large board contains many high-powered devices the 2 oz's may
be needed to minimize plane impedance (voltage drop). The same
thing applies to any board that supplies or passes-through power
to a plug-in. Similarly, 2 oz`s can be a band aid for a design
that has improper combinations of anti-pad size and via-to-via
spacings (inadequate webs).
In some rare cases, we've needed to use 2 oz copper to make up
thickness on difficult/critical impedance stackups, usually in a
trade-off against standard material thicknesses and narrow windows
for line widths.
On the other hand, a great many part numbers (primarily in the 80's)
were specified with a "rubber stamp" for 2 oz copper, and this may
still happen today.
Good luck figuring out which case your looking at!
Jeff Seeger
Applied CAD
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