Explore the cross-section of a PCB. Learn what each layer does and how 2, 4, 6, and 8-layer stackups differ.
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A PCB is built from alternating layers of copper and dielectric (insulating) material. The diagram shows a cross-section. Select '2-layer' to start with the simplest stackup.
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The orange layers are copper, the tan layers are the FR4 core and prepreg.
A 2-layer board has one copper layer on top (components side) and one on the bottom. The FR4 core provides mechanical rigidity. Suitable for simple boards < 50 MHz.
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2-layer boards are the cheapest option. Most hobby boards (Arduino shields, breakouts) are 2-layer.
Switch to 4-layer. Notice two inner copper layers: L2 (GND plane) and L3 (PWR plane). These provide a solid return path for signals routed on L1 and L4.
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Inner planes give controlled impedance and excellent EMI performance. 4-layer is standard for most commercial products.
The prepreg (partially cured epoxy) is the adhesive that bonds core sub-stacks together during lamination. Its dielectric constant (εr ≈ 4.2) affects trace impedance.
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Prepreg is lighter tan than the core. It's flexible before curing, rigid afterwards.
Try 6-layer and 8-layer. As layer count grows, inner signal layers get buried between ground planes, improving signal integrity and EMI shielding.
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High-density designs (FPGAs, DDR memory, RF) typically need 6–8+ layers.