The minimum permissible values for conductor trace width/spacing and annual ring, depending on the copper thickness, can be found in the following table.
Outer* and Inner layers
| Copper thickness Outer* and Inner layers | Standard Min. conductor trace width | -space | annular ring | Special production Min. conductor trace width | -space | annular ring |
| 18µm | 100µm | 100µm | 100µm | 75µm | 75µm | 75µm |
| 35µm | 100µm | 100µm | 100µm | 90µm | 90µm | 100µm |
| 70µm | 150µm | 150µm | 150µm | 150µm | 150µm | 130µm |
| 105µm | 225µm | 225µm | 225µm | 200µm | 200µm | 170µm |
| 140µm | 300µm | 300µm | 300µm | 250µm | 250µm | 200µm |
| 175µm | 400µm | 400µm | 400µm | 280µm | 280µm | 240µm |
| 210µm | 450µm | 450µm | 450µm | 300µm | 300µm | 280µm |
| 245µm | 475µm | 475µm | 475µm | 350µm | 350µm | 320µm |
| 280µm | 500µm | 500µm | 500µm | 380µm | 380µm | 350µm |
| 315µm | 525µm | 525µm | 525µm | 380µm | 380µm | 350µm |
| 350µm | 550µm | 550µm | 550µm | 380µm | 380µm | 350µm |
| 385µm | 575µm | 575µm | 575µm | 380µm | 380µm | 350µm |
| 400µm | 600µm | 600µm | 600µm | 380µm | 380µm | 350µm |
| 455µm | 700µm | 700µm | 700µm | 380µm | 380µm | 350µm |
| 490µm | 700µm | 700µm | 700µm | 380µm | 380µm | 350µm |
| 525µm | 700µm | 700µm | 700µm | 380µm | 380µm | 350µm |
| 560µm | 800µm | 800µm | 800µm | 380µm | 380µm | 350µm |
Effect of the copper thickness on the line resistance
In the favourable pool service for 4 layers, either 18µm or 35µm copper is possible on the inner layers (standard: variable layer buildup). The influence on the line resistance and voltage drop is negligible in most cases.
With standard copper thicknesses, we generally recommend using the largest possible conductor track widths/copper areas on the power and ground layers.
Example of the resistance of a 100mm wide conductor with a length of 100mm on the inner layer
| Copper thickness | Conductor diameter | Line resistance |
|---|---|---|
| 18µm ≙ | 1.8 mm² | 0.0012 Ohm |
| 35µm ≙ | 3.5 mm² | 0.0006 Ohm |