The camera (or photo-tool preparation) department at all good PCB shops can
measure the amount of copper on any layer as a percentage of the total
surface area of the board. This is done optically by measuring the black
areas of the positive film (the circuitry or the Copper) and dividing it by
the board area. This way the copper on certain layer could be compared to
the copper on any other layer and the required addition of copper needed for
balancing could be determined. Different manufacturers would use different
patterns for the added Copper (square pads, round pads, solid copper,
.....). The balancing Copper should be added in the areas that are free of
or not dense with circuitry and would be better if it is balanced within the
layer itself. Off course it should not violate the minimum spacing of the
circuitry. An OEM that I used to work for several years back specified 10%
as the limit of copper variation from layer to layer.
Sherif
----- Original Message -----
From: "Tempea, Ioan" <[log in to unmask]>
To: <[log in to unmask]>
Sent: Friday, February 23, 2007 11:10 AM
Subject: [TN] Copper balancing
Dear colleagues,
very often, the PCB layout designers would draw the circuitry and write a
note on the fab drawing asking that the copper be balanced by the PCB house,
by adding non-functional copper.
The question I have is: how does the PCB house know how much copper to add
and where to add it? Are there any scientific bases, some calculations, or
is it based on experience? 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?
And to make it tougher: if we leave the latitude of choosing the right
substrate and doing the balancing to the board shop, can they guarantee
stable boards?
Thanks,
Ioan
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