Trace capacitance

Trace capacitance calculation Capacitance component of transmission lines (Stripline)

Trace width

Length

Dielectric thickness

Dielectric constant

εr

Trace capacitance (inner layer)

1.81pF

History

Press Enter in any field to keep a snapshot here.

Formula

Trace capacitance (inner layer): C = εr × L × (0.441 + W/2h) / (30×π×0.3) [pF]
(W: trace width, L: length, h: dielectric thickness)

Design notes

An inner-layer trace (stripline) has parasitic capacitance to the ground planes above and below it. That capacitance slows the signal edge and degrades high-speed signals.

Design impact:
• More capacitance means a longer rise time
• It forms an RC filter together with the driver output impedance
• On fast buses it acts as a capacitive load and limits bandwidth

To reduce parasitic capacitance: use a narrower trace, a thicker dielectric, or a board material with a lower dielectric constant.