Common substrates
| Material | Dk | Df (loss tangent) | Tg | Use |
|---|---|---|---|---|
| Standard FR-4 | ~4.3 | 0.020 @ 1 GHz | 130–140 °C | General purpose |
| High-Tg FR-4 (FR-4 S1000-2M etc.) | ~4.3 | 0.018 | 170–180 °C | Automotive, lead-free rework |
| Halogen-free FR-4 | ~4.3 | 0.020 | 150 °C | RoHS-sensitive markets |
| Isola FR408HR | 3.69 | 0.0096 @ 1 GHz | 180 °C | Mid-range digital > 5 Gbps |
| Isola I-Speed | 3.66 | 0.006 @ 1 GHz | 200 °C | High-speed digital |
| Rogers 4350B | 3.48 | 0.0037 @ 10 GHz | 280 °C | RF up to ~10 GHz |
| Rogers 4003C | 3.55 | 0.0027 @ 10 GHz | 280 °C | RF, low-cost alt to PTFE |
| Rogers RO3003 / RT5880 | 3.00 / 2.20 | 0.001 / 0.0009 | > 280 °C | mmWave, very high frequency |
| Polyimide (Kapton) | 3.4 | 0.002 | > 300 °C | Flex PCB |
| Aluminum core (MCPCB) | 4.5 (dielectric) | 0.03 | 140 °C | LED, high-power |
| Ceramic (Al₂O₃) | 9.8 | < 0.001 | > 1000 °C | High-power, high-frequency |
Copper weights
| Copper | Thickness | Use |
|---|---|---|
| 0.5 oz | 17 µm | Fine-pitch / high-density |
| 1 oz | 35 µm | Standard |
| 2 oz | 70 µm | Higher current |
| 3 oz | 105 µm | Power electronics |
| 4 oz+ | 140 µm+ | Heavy copper, bus bars |
Key properties
| Dk (dielectric constant) | Affects impedance and propagation speed |
|---|---|
| Df (loss tangent) | Signal loss per inch at high frequency |
| Tg (glass transition) | Temp at which substrate softens — matters for lead-free reflow |
| CTE | Thermal expansion — critical for reliability of plated holes |
| Moisture absorption | Affects long-term reliability and Dk stability |
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