4- and 6-layer PCB stack-up: a practical guide
Which signal, ground and power layers go where, why the stack must be symmetrical, and what to tell your manufacturer.
What a stack-up is
A multilayer board is built from copper layers separated by insulating FR4: cores (rigid laminate with copper on both sides) and prepreg (glass cloth with partly cured resin that bonds the cores together under heat and pressure). The order and spacing of these layers is the stack-up. It decides signal quality, noise, the board thickness and whether the board stays flat.
Typical 4-layer stack-up
| Layer | Use |
|---|---|
| L1 (top) | Components and signals |
| L2 | Ground plane |
| L3 | Power plane or additional signals |
| L4 (bottom) | Components and signals |
A solid ground plane directly under the top layer gives signals a short return path and reduces noise. A 4-layer board is the usual step up from a 2-layer board when routing becomes dense or noise becomes an issue.
Typical 6-layer stack-up
| Layer | Use |
|---|---|
| L1 (top) | Components and signals |
| L2 | Ground plane |
| L3 | Signals |
| L4 | Signals |
| L5 | Power plane |
| L6 (bottom) | Components and signals |
Two internal signal layers sit between two reference planes, which suits denser designs, mixed analog and digital circuits and higher speeds.
Design rules that matter
- Keep the stack symmetrical around the centre: equal copper and dielectric thickness above and below. An asymmetric stack bows and twists during soldering.
- Give every signal layer an adjacent plane so that return currents have a short, continuous path.
- Avoid splitting planes under fast signals.
- Distribute copper evenly on each layer; large empty areas next to heavy copper areas increase warpage. Copper pours help.
- Plan the vias: plated through-holes connect all layers; keep the smallest drill and the pad size within the manufacturer’s limits (minimum drill 0.3 mm with a 0.5 mm pad at PCB-ELECTRA).
What PCB-ELECTRA offers
- 4- and 6-layer FR4 boards, thickness 0.51–2.4 mm, copper 18, 35, 50 or 70 µm, glass transition temperature Tg 135 °C (standard), 150 °C or 170 °C.
- Maximum size 335 × 440 mm for multilayer boards.
- Every board is tested with a 100% electrical test (short circuit and open circuit, flying probe) and AOI inspection, including the inner layers, at no extra charge.
- Controlled impedance is not available yet — if your design needs it, contact us to discuss the requirement.
What to specify when you order
Number of layers, total thickness, copper weight per layer, Tg, solder mask and silkscreen colour, and the Gerber set with all inner layers and the drill files (see the Gerber guide). Details of the construction are on the 4-layer and 6-layer pages. Configure the board in the price calculator to see the price in euros immediately.
Frequently asked questions
What is the usual stack-up of a 4-layer board?
Signal, ground, power, signal: the outer layers carry the components and signals, the inner layers carry ground and power.
Can I define the stack-up myself?
State the finished thickness and the copper weight of each layer. We confirm the stack-up and contact you if it needs to change.
Do you offer controlled impedance?
Not at the moment. If your design depends on it, tell us in the request.
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