Backdrilling eliminates unused via barrels below the last connected layer, reducing stub-induced resonances and improving return loss/insertion loss for 10–56G SerDes. Typical flow: identify critical nets → define target backdrill depth → specify tolerance (e.g., residual stub < 8–10 mil) → validate with TDR and eye diagrams.

Key points: choose suitable drill sizes/backdrill tools, control aspect ratio, maintain pad/antipad clearances, and coordinate with hybrid stackups. See also: High-Speed PCB · Impedance Control