Trace width and current
A trace is a resistor too. Set the width from copper thickness and allowed temperature rise, and reinforce with planes and vias where it falls short.
Guideline
Enter the current, copper thickness and allowed temperature rise into an IPC-2152 calculator (KiCad's built-in calculator, Saturn PCB Toolkit) to get the width.
| Current | Roughly, 1 oz outer layer, 10 °C rise |
|---|---|
| 0.5 A | 0.3 mm |
| 1 A | 0.5 mm |
| 3 A | 1.8 mm |
| 10 A | 8 mm or more → a plane or 2 oz copper recommended |
(These are rough values; check a real design with a calculator.)
Wider on inner layers
Inner layers cannot shed heat to the air, so the same current needs a wider trace.
Vias have a current limit too
Reckon about 1 A for a single 0.3 mm via. Where a high-current path changes layers, place several vias side by side.
RoadmapSee where this note sits in PCB Design→Check the voltage drop as well
A trace of 1 oz copper, 1 mm wide and 100 mm long has a resistance of about 50 mΩ. At 3 A that is a 150 mV drop. On a motor supply line or a sensing reference, that cannot be ignored.
Practical tips
Lay high-current paths as wide polygons (copper pour); another method is to remove the solder mask and build up thickness with solder.