PCB Impedance Calculator Online

PCB Impedance Formula:

\[ Z = \frac{60}{\sqrt{\epsilon_r}} \times \ln\left(\frac{1.9 (2h + t)}{0.8 w + t}\right) \]

Relative Permittivity (εr):

dimensionless

Dielectric Height (h):

meters

Trace Thickness (t):

meters

Trace Width (w):

meters

Characteristic Impedance (Z): ohms

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1. What is a PCB Impedance Calculator?

Definition: This calculator estimates the characteristic impedance of a microstrip transmission line on a printed circuit board (PCB).

Purpose: It helps PCB designers achieve proper impedance matching for high-speed digital circuits and RF applications.

2. How Does the Calculator Work?

The calculator uses the microstrip impedance formula:

\[ Z = \frac{60}{\sqrt{\epsilon_r}} \times \ln\left(\frac{1.9 (2h + t)}{0.8 w + t}\right) \]

Where:

\( Z \) — Characteristic impedance (ohms)
\( \epsilon_r \) — Relative permittivity of the dielectric material
\( h \) — Height of dielectric substrate (meters)
\( t \) — Thickness of the copper trace (meters)
\( w \) — Width of the trace (meters)

Explanation: The formula calculates the impedance based on the physical dimensions and dielectric properties of the PCB stackup.

3. Importance of Impedance Matching

Details: Proper impedance matching minimizes signal reflections, reduces EMI, and ensures signal integrity in high-speed circuits.

4. Using the Calculator

Tips: Enter the dielectric constant (εr), substrate height, trace thickness, and trace width. All values must be > 0.

Typical Values:

FR4 εr: 4.3 (range 4.1-4.8)
Standard PCB height: 1.6mm (0.0016m)
1oz copper thickness: 35μm (0.000035m)

5. Frequently Asked Questions (FAQ)

Q1: Why is impedance matching important?
A: Impedance mismatches cause signal reflections that degrade signal quality and increase EMI in high-speed circuits.

Q2: What's a typical target impedance?
A: Common values are 50Ω for RF and 100Ω for differential pairs, but check your specific design requirements.

Q3: How accurate is this calculator?
A: It provides a good estimate (≈5% accuracy) for standard microstrip designs. For precise calculations, use field solvers.

Q4: What affects PCB impedance most?
A: Trace width and dielectric height have the greatest impact, followed by dielectric constant.

Q5: How do I adjust impedance?
A: Change trace width (narrower = higher Z), dielectric height (thicker = higher Z), or use materials with different εr.