1. What is PCB Trace Impedance?

Definition: Characteristic impedance is the resistance to signal propagation in a transmission line (PCB trace) at high frequencies.

Purpose: Proper impedance matching is crucial for signal integrity in high-speed digital and RF circuits.

2. How Does the Calculator Work?

The calculator uses the microstrip impedance formula:

Where:

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

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

3. Importance of Impedance Control

Details: Proper impedance matching minimizes signal reflections, reduces EMI, and ensures reliable high-speed data transmission.

4. Using the Calculator

Tips: Enter the relative permittivity (ε_r) of your substrate (4.3 for FR4), dielectric height, trace width, and trace thickness (typically 0.035mm for 1oz copper).

5. Frequently Asked Questions (FAQ)

Q1: What's a typical impedance target?
A: Common values are 50Ω for RF and 90Ω for differential pairs, but always check your specific design requirements.

Q2: How accurate is this calculator?
A: It provides good estimates (±5%) but for precise results, use field solvers or manufacturer tools.

Q3: What affects impedance the most?
A: Trace width and dielectric height have the greatest impact. Doubling width roughly halves the impedance.

Q4: What's ε_r for common materials?
A: FR4: ~4.3, Rogers 4350: 3.48, Polyimide: 3.5, Air: 1.0

Q5: How does frequency affect impedance?
A: This formula works well up to a few GHz. At higher frequencies, dispersion effects become significant.