1. What is PCB Trace Propagation Delay?

Definition: Propagation delay is the time it takes for a signal to travel from one point to another through a PCB trace.

Purpose: This calculator helps electronics engineers estimate signal delays in PCB designs, critical for high-speed digital circuits.

2. How Does the Calculator Work?

The calculator uses the formula:

Where:

• Delay — Signal propagation time (seconds)
• length — Trace length (meters)
• ε_r — Relative permittivity of the PCB material (dimensionless)
• c — Speed of light in vacuum (299,792,458 m/s)

Explanation: The delay increases with trace length and the square root of the dielectric constant.

3. Importance of Propagation Delay Calculation

Details: Accurate delay calculation is crucial for signal integrity, timing analysis, and ensuring proper synchronization in high-speed designs.

4. Using the Calculator

Tips: Enter the trace length in meters and the relative permittivity (ε_r) of your PCB material (default 4.3 for FR4).

5. Frequently Asked Questions (FAQ)

Q1: What's a typical ε_r value for common PCB materials?
A: FR4: ~4.3, Rogers 4350: ~3.48, PTFE: ~2.1. Check your material datasheet for exact values.

Q2: Why does permittivity affect signal speed?
A: Higher ε_r increases capacitance, slowing the electromagnetic wave propagation.

Q3: How does this relate to signal integrity?
A: Delays affect timing margins, skew, and can cause signal reflections if not properly managed.

Q4: What's a typical delay per unit length?
A: For FR4 (ε_r=4.3), about 143 ps/inch or 56.3 ps/cm.

Q5: How accurate is this calculation?
A: It provides a good estimate, but actual delays may vary slightly due to trace geometry and manufacturing variations.