Re: [SI-LIST] : Different oz copper for grounds

Mitch Morey (mitch.morey@nsicomm.com)
Tue, 21 Sep 1999 08:30:07 -0700

And the guessing games continue...

Hi Chris,

I get such a kick out of email "workgroups". With all of today's technologies, I still find questions being asked that I heard in the 80's.

Couple things. #1, you obviously work for Cadence, so why do you have questions regarding thermal issues. I would've thought YOU, of most all people would have available the best thermal tools to solve your problems. #2, it's
been a while since I've used 1 oz. copper for the signal layers, and been forever (the 80's) since I've used 2 oz. CU for anything. Why are you not using 1/2 oz. CU for the signal layers, and 1 oz. CU for the planes and some sort
of thermal attachment for your hot parts? I kind of get the assumption this is not a "power" board, because you don't mention that it is, so I don't quite see the need for the thermal "layer".

Questons, questions, questions. But, if you do have to go with the 2 oz. CU, it'll only cost you the dough, and more stackup height. The should be no negative effects, done in a quality fab house.

G'day!

Mitch
Sr PCB Designer
San Diego, CA

Chris Bobek wrote:

> Hi,
>
> This should be a quick question. We are doing a 12 layer board and it
> has a thermal layer on layer 2 (it's really just a plane with no
> electrical connection to anything). To keep the symmetry of the
> stackup, we have to add a third ground plane as layer 11. We were going
> to use 1oz copper for everything, but now the thermal guys are
> considering 2oz copper for the thermal plane. Will there be any
> negative effect if the ground plane is increased to 2oz copper while the
> other two ground planes (and all of the other signals) are still 1oz?
>
> I assume there won't be problem, but it never hurts to ask.
>
> Thanks,
>
> Chris
>
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