50Ω Microstrip Calculator
Controlled Impedance | FR-4 (Er=4.5) | IPC-2141
For 50Ω microstrip on FR-4 with 0.2mm dielectric:
Impedance Parameters
MOD: IMP_CAL_V1Impedance Check
Understanding 50Ω Microstrip Impedance
50Ω is the most common single-ended impedance in PCB design, used for USB, SATA, and most RF applications. To achieve 50Ω characteristic impedance using a microstriptrace on standard FR-4 material (Er=4.5) with 0.2mm dielectric height, you need a trace width of approximately 0.333mm (13.1 mil). This calculation follows the IPC-2141 standard and Hammerstad equations for accurate impedance control.
Key Parameters for 50Ω Design
- Target Impedance: 50Ω (characteristic impedance Z₀)
- Trace Type: Microstrip (surface layer with air above)
- Required Width: 0.333mm (13.1 mil)
- Dielectric Constant: 4.5 (FR-4 standard)
- Dielectric Height: 0.2mm (layer spacing)
- Copper Thickness: 35µm (1oz copper)
- Effective Er: 3.359
- Propagation Delay: 6.113 ps/mm
Microstrip vs Stripline for 50Ω
Microstrip traces are routed on the outer layers of the PCB with air above the trace. This results in a lower effective dielectric constant (3.36 vs 4.5 for stripline), requiring a different trace width to achieve 50Ω. Microstrip is preferred for high-frequency designs due to lower propagation delay and easier access for probing.
Common 50Ω Applications
50Ω impedance is required by the following standards and interfaces:
50Ω Standard Applications
IPC-2141 Impedance Formula
For microstrip, the characteristic impedance is calculated using the Hammerstad & Jensen formula, which accounts for the effective dielectric constant created by the air-dielectric interface. The formula considers trace width (W), dielectric height (H), copper thickness (T), and material properties to accurately predict impedance within ±5% tolerance.
Frequently Asked Questions
How tight should my 50Ω trace width tolerance be?
Most high-speed interfaces require ±10% impedance tolerance. For a 50Ω target, this means45Ω to 55.00000000000001Ω is acceptable. Specify controlled impedance to your PCB manufacturer and expect trace width tolerance of ±0.5-1 mil to achieve this.
Does copper thickness affect 50Ω impedance?
Yes, thicker copper slightly lowers impedance due to increased effective trace width. For precision designs, always include copper thickness in your impedance calculations. Our calculator uses35µm (1oz) as the standard.
What if my PCB uses different dielectric than FR-4?
High-speed designs often use low-loss materials like Rogers 4350B (Er=3.48) or Megtron 6 (Er=3.4). Lower Er requires wider traces for the same impedance. Use our full calculator above to input your specific material properties.
Related Impedance Calculations
Complete Your PCB Design
After calculating 50Ω microstrip trace width, use our other free tools to complete your high-speed PCB design. Calculate trace current capacity and via sizing for your power delivery network.