Via Inductance

Formula

Description

Every via in a PCB has parasitic inductance due to its length and cylindrical geometry. This inductance creates impedance discontinuities in high-speed signal paths and adds parasitic inductance to power delivery networks. A typical through-hole via in a standard 1.6mm board has about 0.5-1.5 nH of inductance. At GHz frequencies, even 1 nH presents significant reactance (6.3Ω at 1 GHz). Minimizing via inductance is critical for high-speed designs, which is why shorter vias (blind, buried, or microvias) are preferred.

Variables

• L — Via inductance (nH)
• h — Via height (length through the board) (mm)
• d — Via drill diameter (mm)

Practical Notes

The result is in nanohenries. Wider diameter reduces inductance slightly, but the logarithmic dependence means doubling the diameter only reduces inductance by about 15%. Multiple vias in parallel reduce effective inductance: two vias ≈ L/2 if well-separated. Return path vias (ground stitching vias near signal vias) are essential to minimize loop inductance and control impedance at layer transitions.