Trace Impedance

Controlled impedance for microstrip and stripline, single-ended or differential, with the width for a target, delay, loss, and the fabrication spread

Line Type

Structure

Signaling

Target Impedance(Z₀)

Trace Geometry

Trace Width(W)

µm

Copper Thickness(T)

µm

Stackup

Dielectric Height (trace to plane)(H)

µm

Dielectric Constant(εr)

Loss Tangent(tan δ)

×10⁻³

Loss

Frequency(f)

GHz

Copper Roughness (RMS)(Δ)

µm RMS

Fabrication Tolerance

Etch Tolerance on Width (±)(ΔW)

µm

Dielectric Thickness (±)(ΔH)

Dielectric Constant (±)(Δεr)

Solder mask not modelled

Mask over a surface microstrip typically lowers Z by 1–3 Ω single-ended and 2–6 Ω differential. Fabs include it in their controlled-impedance solver — aim slightly high or ask the fab for the masked value.

Closed-form estimate — sign off with your fab

Closed-form quasi-static models (no dispersion, no solder mask, rectangular copper). Fabricators hold controlled impedance to ±10 %; sign off the stackup with your fab’s field solver.

On Target−0.2 %

49.92

Z₀ (Ω)?

5.65

Delay (ps/mm)?

179.4

Width for Target (µm)?

Results

Characteristic Impedance(Z₀)?

49.92Ω

Effective Permittivity(εeff)?

2.873

Propagation Delay(tpd)?

5.65ps/mm

Width for Target(W)?

179.4µm

Fab Corner — Low(Zmin)?

44.2Ω

Fab Corner — High(Zmax)?

56.0Ω

Dielectric Loss(αd)?

2.682dB/m

Conductor Loss(αc)?

3.490dB/m

Total Loss(α)?

6.172dB/m

Skin Depth(δ)?

2.090µm

Impedance vs Trace Width

Loss vs Frequency

Total
Conductor
Dielectric

Created by Catlynn Nguyen & Jie Chai · 2026