2-layer
- Top: signals / components; bottom: signals / GND pour.
- Only option for very cheap boards — poor EMI, poor SI above 50 MHz.
- Make bottom layer a continuous ground pour wherever possible.
4-layer (common)
| Layer | Use |
|---|---|
| Top | Signal + components |
| L2 | Solid GND plane |
| L3 | Power plane (or second GND + routed power) |
| Bottom | Signal + components |
6-layer
| Layer | Use |
|---|---|
| Top | Signal |
| L2 | GND |
| L3 | Signal (routed between planes for SI) |
| L4 | Power |
| L5 | GND |
| Bottom | Signal |
8-layer (typical BGA-heavy)
| Layer | Use |
|---|---|
| Top | Signal + BGA escape |
| L2 | GND |
| L3 | Signal |
| L4 | Power |
| L5 | Power |
| L6 | Signal |
| L7 | GND |
| Bottom | Signal |
Rules of thumb
- Reference plane under every signal layer: ideally GND, or power with plenty of decoupling.
- Symmetric stackup: balance copper on both sides to prevent warpage.
- Signal-signal adjacent layers: route orthogonally to minimize crosstalk.
- Controlled impedance: trace width/height determined by the specific stackup — ask fab for their dielectric thickness.
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