> 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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