PCB design glossary
Stack-up
AKA: stackup, layer stack
The arrangement of copper, prepreg, and core layers in a PCB, from top to bottom.
The stack-up specifies what each layer of the PCB is — signal, plane, prepreg, core — and how thick each is. It determines the board's mechanical thickness, controlled-impedance characteristics, and cost.
Common stack-ups are 2-layer (1.6 mm total) and 4-layer (1.6 mm with two inner planes), but production hardware often runs 6, 8, or more layers with carefully tuned dielectrics.
Common stack-ups
- 2 layers: top and bottom copper on a 1.6 mm core. Cheapest, fine for simple boards.
- 4 layers: signal, ground, power, signal. The most common upgrade, with solid planes for noise and routing.
- 6 layers and more: extra signal and plane layers for dense, high-speed boards.
Cores, prepreg and impedance
A multilayer board is built from cores (cured laminate with copper on both sides) bonded together with prepreg (uncured resin sheets). The thickness of the dielectric between a trace and its reference plane, and the material's dielectric constant (around 4.2 to 4.6 for FR-4), set the trace's impedance. That is why impedance-controlled boards use the fab's published stack-up.
Choosing a stack-up
- Put a ground plane next to every high-speed signal layer.
- Keep the stack symmetrical so the board does not warp.
- Use your fab's standard stack-ups where possible: they are cheaper and the impedance data is known.
Work it out with a free tool
Pick a stack-up before you route
Layer order and dielectric thickness fix your impedances. Start from a 2, 4, 6 or 8-layer preset in the stackup planner and adjust from there.
Open the stackup planner