1. What is Trace Impedance?

Trace impedance (z₀) is the characteristic impedance of a PCB trace, representing the opposition to alternating current. Proper impedance control is crucial for signal integrity in high-speed digital and RF circuits.

2. How Does the Calculator Work?

The calculator uses the trace impedance equation:

Where:

• \( \epsilon_r \) — Dielectric constant of the substrate
• \( h \) — Height of trace above reference plane (mil)
• \( t \) — Thickness of the copper trace (mil)
• \( w \) — Width of the trace (mil)
• \( z_0 \) — Characteristic impedance (ohm)

Explanation: The equation accounts for the geometry of the trace and the dielectric properties of the PCB material.

3. Importance of Trace Impedance

Details: Proper impedance matching prevents signal reflections, reduces EMI, and ensures signal integrity in high-speed circuits. Critical for USB, HDMI, DDR memory, and RF applications.

4. Using the Calculator

Tips: Enter all dimensions in mils (1 mil = 0.001 inch). Typical values: ε_r≈4.3 (FR4), h≈5-10 mil, t≈1.4 mil (1 oz copper), w≈5-15 mil.

5. Frequently Asked Questions (FAQ)

Q1: What's a typical trace impedance value?
A: Common values are 50Ω (RF), 75Ω (video), 90Ω (USB differential), and 100Ω (Ethernet differential).

Q2: How accurate is this calculator?
A: This provides a good estimate for surface microstrips. For precise designs, use field solvers or manufacturer's tools.

Q3: What affects trace impedance most?
A: The three main factors are trace width, height above plane, and dielectric constant.

Q4: How does copper thickness affect impedance?
A: Thicker copper slightly reduces impedance (typically <5% effect for 1oz vs 2oz copper).

Q5: What about differential pairs?
A: Differential impedance depends on spacing between pairs and requires a different calculation.