It’s common practice to balance copper between the top and bottom layers of a PCB to reduce warpage and fabrication issues.
Is there a practical way to quantify copper balance (for example, percentage coverage per layer), rather than judging it subjectively? Are there general guidelines for what constitutes an acceptable imbalance, and do these limits depend on factors such as board size, copper weight, or FR-4 thickness?
Some ECAD and most CAM tools may have a feature that wil provide copper coverage insight.
The simpler, less scientific solution is to pour copper into open areas of all copper layers. Keep in mind that doing that can influence net impedances or electrical isolation clearances depending on the stackup.
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Copper balance is mainly a fabrication concern, not a strict percentage rule. While CAD/CAM tools can report copper coverage per layer, fabs don’t usually enforce fixed ratios like 50/50. What matters is avoiding gross asymmetry that causes uneven shrinkage during lamination. Larger boards, heavier copper, and thinner cores are more sensitive; small boards with light copper are more forgiving.
Best practice is to keep copper reasonably symmetric layer-to-layer and check with your fabricator for stackup-specific warpage limits rather than relying on a universal percentage.
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