PCB Microstrip / Stripline Impedance Calculator
Estimate single-ended PCB transmission-line impedance, effective dielectric constant, propagation velocity, and delay for microstrip or stripline geometry.
Engineering tool
PCB Microstrip / Stripline Impedance Calculator
Estimate characteristic impedance, effective dielectric constant, propagation velocity, and delay.
Result console
- Characteristic impedance Z0
- 71.1838Ω
- Effective dielectric constant
- 3.0077
- Propagation velocity
- 172,863,046.7615m/s
- Velocity
- 57.6609% of c
- Delay
- 5.7849ps/mm
- Delay
- 146.9371ps/in
- Geometry ratio W/H
- 0.8333
Use this closed-form result for early stackup exploration. Confirm finished geometry, dielectric data, solder mask, copper roughness, and etching compensation with the PCB manufacturer or a field solver.
Formula reference
Transmission Line Formulas
Simplified closed-form equations support early stackup exploration.
Microstrip Z0 ≈ 87/√(Er+1.41) × ln[5.98H/(0.8W+T)]Eeff ≈ (Er+1)/2 + (Er-1)/(2√(1+12H/W))Stripline Z0 ≈ 60/√Er × ln[4H/(0.67π(W+T))]v = c/√EeffDelay per length td = 1/vVariable definitions
- W
- trace width
- H
- dielectric height
- T
- copper thickness
- Er
- dielectric constant
- For stripline, Eeff ≈ Er
Worked Example
For W = 0.15 mm, H = 0.18 mm, T = 35 µm, and Er = 4.2, select Microstrip to estimate Z0, effective dielectric constant, propagation speed, and delay per millimeter or inch.
Engineering Notes
- Controlled impedance depends on stackup geometry and dielectric constant.
- Microstrip fields partly travel through air and solder mask.
- Stripline is more shielded but depends on distance to reference planes.
- Copper thickness, roughness, solder mask, and fabrication tolerance affect real impedance.
- Final controlled impedance should be verified by the PCB manufacturer or field solver.
Support reference
FAQ
What is PCB characteristic impedance?
Characteristic impedance is the voltage-to-current ratio of a traveling wave on a PCB transmission line, determined by conductor geometry and surrounding dielectric materials.
What is the difference between microstrip and stripline?
Microstrip runs on an outer layer above one reference plane, while stripline is embedded between reference planes and is more electromagnetically shielded.
How do trace width and dielectric height affect impedance?
A wider trace generally lowers impedance, while increasing dielectric height generally raises impedance for the same trace width.
What is effective dielectric constant?
Effective dielectric constant represents the combined field distribution through dielectric and air. For stripline the field is largely inside the dielectric, so Eeff is approximated as Er.
Why should impedance be verified by the PCB manufacturer?
Finished dielectric thickness, resin content, copper thickness, etching, roughness, and solder mask differ from nominal values. Manufacturers use production stackups and field solvers.
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