The best designs use the least amount of material possible.
Why evenly distribute copper on a PCB? Look at the material stackup as it alternates between conductor and dielectric material. The goal is to build a mirror image of copper weights as you work outward from the centerline.
Going beyond specifying alternating shape and route layers, the “greenest” PCB involves a minimum of etching. It’s intuitive that removing less material requires less time in the solvent tanks. Time is money, so that should be reason enough to have all layers biased toward copper fill.
Besides being easier on the equipment, copper-biased design will help maintain an even thickness across the entire board. While fabricators generally offer a +/-10% thickness tolerance, we often want a tighter distribution when it comes to the actual PCB thickness.
Basically, we must permit the 10% thickness tolerance, while aiming for a 5% variance by providing artwork that makes the most of the raw materials. The more evenly we design the board, the more consistent the outcome.
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