PCB copper thickness: from ounces to microns
How to read "1 oz" on a datasheet, which copper weights you can order and how the choice changes the minimum trace and spacing.
What "oz" means
Copper weight is given in ounces per square foot: the thickness a layer of copper has when one ounce of it is spread evenly over one square foot. One ounce corresponds to about 35 µm.
| Copper weight | Thickness | Typical use |
|---|---|---|
| 0.5 oz | about 18 µm | Fine traces, signal-only designs |
| 1 oz | about 35 µm | Standard choice for most boards |
| 1.5 oz | about 50 µm | Higher currents without very wide traces |
| 2 oz | about 70 µm | Power paths, LED drivers, motor controllers |
PCB-ELECTRA offers 18, 35, 50 and 70 µm copper.
Base copper and final copper
The laminate comes with a base copper foil. On boards with plated through-holes the outer layers also receive plated copper during the hole-plating process, so the final copper on the outside is thicker than the base foil. The two numbers matter: the base copper sets what can be etched, and the final copper sets the current capacity.
How copper thickness changes the minimum trace and spacing
Etching works from the surface downwards and also removes some copper from the sides of a trace, so thicker copper needs more spacing.
| Base copper | Minimum trace / spacing |
|---|---|
| 18 µm (up to 35 µm final) | 0.15 mm / 0.15 mm |
| 35 µm (up to 55 µm final) | 0.22 mm / 0.22 mm |
| 70 µm (up to 90 µm final) | 0.28 mm / 0.28 mm |
With more final copper the recommended values grow further; the exact table is on the capabilities page.
Choosing the copper weight
- 35 µm is the sensible default for most designs.
- 18 µm suits very fine traces and spacing.
- 50 and 70 µm suit power paths: instead of making traces very wide, increase the copper. See the guide values in the trace width and current guide.
- On multilayer boards the copper weight is chosen per layer; inner layers are often thinner than outer ones.
- Keep the copper weight the same on both sides of a board where possible, because unequal copper bends the board during soldering.
- Thicker copper costs more, and so does a finer trace class; pick what the current really requires.
Select the copper weight in the price calculator and see the price in euros immediately. If you are unsure, contact us.
Frequently asked questions
Which copper thicknesses do you offer?
18, 35, 50 and 70 µm.
Why does thicker copper limit the fine details?
The etching removes copper sideways as well, so thicker copper needs wider traces and larger spacing. Fine details are possible on thin copper.
When should I choose 70 µm?
When the board carries high currents or has to spread heat, for example in power electronics, and the layout allows wider spacing.
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