1. What is PCB Trace Impedance?

Characteristic impedance is the resistance to current flow in a transmission line when it's infinitely long. In PCBs, controlled impedance is crucial for high-speed signals to prevent reflections and maintain signal integrity.

2. How Does the Calculator Work?

The calculator uses the PCBWay impedance equation:

Where:

• \( Z \) — Characteristic impedance (Ω)
• \( \epsilon_r \) — Dielectric constant of the substrate
• \( h \) — Height of dielectric (mm)
• \( t \) — Trace thickness (mm)
• \( w \) — Trace width (mm)

Explanation: The equation accounts for the relationship between trace geometry, dielectric properties, and resulting impedance.

3. Importance of Impedance Control

Details: Proper impedance matching is essential for high-frequency circuits to prevent signal reflections, reduce EMI, and ensure reliable data transmission.

4. Using the Calculator

Tips: Enter dielectric constant (typically 4.2-4.5 for FR4), dielectric height, trace thickness (typically 0.035mm for 1oz copper), and trace width. All values must be positive.

5. Frequently Asked Questions (FAQ)

Q1: What's typical impedance for PCB traces?
A: Common values are 50Ω for single-ended and 100Ω for differential signals, but requirements vary by application.

Q2: How does dielectric constant affect impedance?
A: Higher ε_r lowers impedance for the same geometry. FR4 typically has ε_r≈4.2-4.5 at high frequencies.

Q3: Why is trace width important?
A: Wider traces have lower impedance. For 50Ω on FR4, typical width is about twice the dielectric height.

Q4: What affects impedance accuracy?
A: Manufacturing tolerances, copper roughness, frequency effects, and variations in dielectric constant.

Q5: When should I use controlled impedance?
A: For signals where the rise time is less than about 6× the propagation delay along the trace (typically >50MHz).