Also be aware that if you have high frequency signals on layer 2,
thieving on layer 1 MAY affect your signals on layer 2. We will
normally do our own thieving on these boards so we can delete it from
areas where it may introduce stray capacitance and inductance in the
signal. This depends on the frequency of the signal and the thickness
of the dielectric between layer 1 and 2, so YMMV...
And, finally, remember that if you are doing a sequential lamination or
HDI board some of your inner layers are actually outer layers at some
point in the process and will have to have thieving added as well.
--
George Patrick
Tektronix, Inc.
Central Engineering, EDS Applications Support
P.O. Box 500, M/S 39-512
Beaverton, OR 97077-0001
* 503-627-5272 (voice) * 503-627-5587 (fax)
http://www.tektronix.com http://www.pcb-designer.com
"Off-Grid and Proud of it!"
-----Original Message-----
From: DesignerCouncil [mailto:[log in to unmask]] On Behalf Of
Mitch S. Morey
Sent: Friday, February 23, 2007 09:12
To: [log in to unmask]
Subject: Re: [DC] Copper balancing
> The question I have is: how does the PCB house know how much copper to
> add and where to add it?
Normally, Door #3) based on experience. This is what pays there
livelyhood! These guys do this for a living. They know what they need to
make their processes work correctly.
> Otherwise said, if the PCB house will balance the copper, this means
the
> warpage worries are gone, or just that there are chances it will warp
>less?
Good fab houses will make sure your board, regardless of material, will
be
processed according to the fab spec you call out in your fabrication
drawing. Normally, IPC-6012 (class 1, 2 or 3). If you don't call out a
fabrication spec, and it will include allowable warpage requirements,
they'll give you what you ask for...
Now, if you've done everything correctly, and called out the proper
specification requirements, etc. and the fab houses botches the job, you
can cancel payment and send the boards back. (and find a better fab
house)
I've only had one BAD, BAD, BAD instance in my last ~18 years, so that
should tell you there are good companies to work with out there. One bad
one I won't have do boards is a place in Toronto I was outsourced to
use.
Never again.
But, and I'll emphasize, if you call out proper standards (specs) to
build
boards to, you've done 90% of the work. They do the rest.
Now, speaking of adding copper features for balancing. This is normally
done to the outer layers to allow a consistant plating surface across
the
entire surface (this is an 'additive' plating process). One thing to
keep
in mind. These features are not connected to anything, so if you have
critical circuits on these layers, make sure you call out the clearance
you require from your critical traces to any other feature (added
copper).
The fab house can accomidate spacing requirements very well, and ensure
proper plating coverage.
Hope this helps. Good day.
Mitch
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