Best design rule practice calls for the same copper weight to be used on the mirror opposite layer in the stack up. It's common for there to be heavier copper on some layers than others, for example having 3oz copper on outer layers but 1oz copper on the inner layers, or vice versa. Can I have more copper on one layer than another? During your design phase, try to evenly distribute your copper across the entire board rather than having large open spaces with isolated features. The chemical solution in the plating and etching tanks are agitated and circulated during processing to minimize these inconsistencies however, a panel with drastically different copper densities can prove problematic. During etch, the intended image is masked off to protect it from the etchant, but the chemicals in the tank dissolve the copper at slightly different rates depending on where the features are on the panel, the panel's placement within the tank itself, and how densely or sparsely the copper features are distributed.
![pcb chemical pcb chemical](https://www.insulationmaterial.co/th/productpic/pb_zonv1574234269.jpg)
![pcb chemical pcb chemical](https://ebcne.org/wp-content/uploads/2021/06/PCBs.png)
There isn't precise control over where the copper is removed from or plated onto. Plating and etching are organic processes in the sense that the copper clad laminate is submerged into a vat of chemicals for processing. Of course, this isn't always possible, but keep this in mind during layout. Not only in regard to the copper thickness on each layer, but also how it's distributed across the layer. The thicker your copper requirements are, the more spacing is required between copper features on your PCB.Ĭopper Distribution should be as even as possibleĪs a general rule, copper should be distributed as evenly as possible throughout your design. A 4-layer board with a defined weight of 1oz, is assumed to have a finished copper thickness of 1.37mils (or more) on every copper layer. TIP: Every copper layer is assumed to have the same finished copper weight unless otherwise specified in your fabrication notes. PCB Prime is not affiliated with the authors of these tools. A few such 3rd party tools are linked below. There are several online tools that can help you determine what thickness, width or length your traces need to be to achieve your target results. If your design requires higher voltages, resistance, or impedances, thicker copper might be necessary. If your files do not include a fab print or other specifications, we'll assume 1oz finished copper weight on all copper layers. Copper Thickness Conversion Chart ozīy a wide margin, most PCBs are made with 1oz copper on each layer. A conversion chart for different units of measure can be found below.
![pcb chemical pcb chemical](https://www.agfa.com/agfa-labs/wp-content/uploads/sites/3/2020/04/case-25-Cross-sectional-chemical-imaging-of-PCB-boards.png)
Why use a unit of weight to specify a thickness? Great question! If 1oz (28.35 grams) of copper is flattened to evenly cover 1 square foot of surface area (0.093 square meter), the resulting thickness will be 1.37mils (0.0348mm). In the printed circuit board industry, the most common way to express copper thickness on a PCB is in ounces (oz).