1. What is a PCB Stack Up Calculator?

Definition: This calculator estimates the characteristic impedance of a PCB trace based on dielectric properties and trace geometry.

Purpose: It helps PCB designers achieve desired impedance values for controlled impedance boards used in high-speed digital and RF circuits.

2. How Does the Calculator Work?

The calculator uses the formula:

Where:

• \( Z \) — Characteristic impedance (Ω)
• \( \epsilon_r \) — Dielectric constant
• \( h \) — Dielectric thickness (mil)
• \( w \) — Trace width (mil)
• \( t \) — Trace thickness (mil)

Explanation: The formula calculates impedance for microstrip traces, accounting for dielectric properties and trace geometry.

3. Importance of Impedance Calculation

Details: Proper impedance matching prevents signal reflections, ensures signal integrity, and maintains power transfer in high-speed circuits.

4. Using the Calculator

Tips: Enter dielectric thickness (h), dielectric constant (εr, default 4.3 for FR4), trace width (w), and trace thickness (t, default 1.4 mil for 1 oz copper). All values must be > 0.

5. Frequently Asked Questions (FAQ)

Q1: What's a typical impedance target?
A: Common values are 50Ω for single-ended and 100Ω for differential signals in digital circuits.

Q2: How accurate is this calculator?
A: It provides a good estimate (within 5-10%) but for precise values, use field solvers or consult your PCB manufacturer.

Q3: What affects impedance the most?
A: Trace width and dielectric thickness have the greatest impact on impedance values.

Q4: What's the standard copper thickness?
A: 1 oz copper (1.4 mil) is standard, but 0.5 oz (0.7 mil) and 2 oz (2.8 mil) are also common.

Q5: How does dielectric constant vary?
A: FR4 typically ranges from 4.2-4.8 depending on frequency and resin content. Special materials may have lower εr.