Stub and back-drilling
A through via that leaves the signal layer continues to the bottom of the board. That unused copper is a stub; the longer it is, the lower the frequency at which it resonates. Back-drilling removes it, at the cost of an extra process step.
Antipads and return path
The antipad around a via removes copper from the plane; if it is too large, the return current detours and the local impedance changes. Keep antipads consistent along a bus and check the plane transition at each via.
Via count and layer changes
Every layer change is a discontinuity. Minimise them on the high-speed nets, keep the reference plane continuous under the signal, and place ground vias near the signal via when the return layer changes.
What we need
Send the stackup, the data rate or frequency band, and the impedance target. We build 1–38 layers, laser vias from 0.1 mm and impedance-controlled boards with ±10% (or ±5% on request) after reviewing the build.
