FR4 Trace Width Calculator
Standard FR4 | High-Tg FR4 | Halogen-Free FR4
Calculate trace width and impedance for FR4 PCB designs. FR4 is the most common PCB laminate material, suitable for most applications up to a few GHz. Get accurate calculations using standard FR4 properties.
FR4 Material Properties
| Property | Typical Value | Notes |
|---|---|---|
| Dielectric Constant (Dk) | 4.2-4.5 | @ 1 MHz |
| Loss Tangent (Df) | 0.02-0.025 | @ 1 MHz |
| Glass Transition (Tg) | 130-180°C | Standard grades |
| Breakdown Voltage | >50 kV/mm | Per IPC-4101 |
When to Use FR4
Ideal For
- • Digital designs up to ~2 GHz
- • USB 2.0, SATA, Gigabit Ethernet
- • Most microcontroller applications
- • Cost-sensitive designs
- • Consumer electronics
- • Industrial controls
Consider Alternatives For
- • High-speed signals >3 GHz
- • PCIe 4.0+ interfaces
- • Long trace runs at high speed
- • RF/microwave applications
- • Low-loss requirements
- • Ultra-tight impedance tolerance
FR4 Design Guidelines
Dk Variation
FR4 Dk varies with frequency, temperature, and resin content. Use Dk=4.3-4.5 for initial calculations, then verify with your fab's stackup.
Loss at High Frequency
FR4 loss increases significantly above 1 GHz. For long high-speed traces, calculate insertion loss to ensure adequate signal margin.
Tg Selection
Choose Tg based on assembly and operating temperature. Standard Tg (130°C) for most applications, High-Tg (170°C+) for lead-free or high-temp operation.
Common FR4 Grades
Standard FR4
High-Tg FR4
Low-Loss FR4 (IS415)
Calculate FR4 Trace Dimensions
Use our free calculator with Dk=4.3-4.5 for standard FR4. Adjust based on your manufacturer's specific stackup documentation.
FR4 FAQ
What Dk should I use for FR4?
Use Dk=4.3-4.5 for initial calculations. The exact value varies by manufacturer and frequency. Always verify with your fab's stackup data.
Is FR4 good for high-speed designs?
FR4 works well up to ~2-3 GHz for short traces. Above that, loss becomes significant. Consider low-loss materials for PCIe 4.0+, 10G+ signals.
What's the difference between Tg levels?
Standard Tg (130°C) is fine for most applications. Use High-Tg (170°C+) for lead-free assembly, high operating temperatures, or increased reliability.
Can I use FR4 for RF designs?
Only for low frequency RF (<1 GHz) with short traces. For serious RF work, use RF-specific materials like Rogers RO4350B or similar.
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