PCB design glossary
Copper Layer
AKA: copper, cu layer
A conductive layer of a PCB — where traces, pads, planes, and vias live.
Copper layers carry the electrical signals. A 2-layer board has top and bottom copper; a 4-layer board adds two inner layers, typically a power plane and a ground plane.
Copper thickness is usually specified in ounces — 1 oz copper is ~35 µm thick and is the standard for prototype boards. Higher-current designs use 2 oz or thicker copper.
Copper weight
Copper thickness is given as weight per square foot. 1 oz copper is about 35 µm thick and is standard for most boards. 2 oz (about 70 µm) carries more current in the same width and is common on power boards. Inner layers are often thinner, such as 0.5 oz, and outer layers gain some thickness from plating.
Copper on each layer
- Signal layers carry traces between pads.
- Plane layers are mostly solid copper tied to ground or a power rail.
- Copper pours fill empty areas with copper, usually connected to ground.
- Keep copper back from the board edge by your fab's minimum edge clearance.
Balancing copper
Large areas of copper on one side and little on the other can make a board warp during reflow. Pouring copper on sparse layers, or adding a thieving pattern, keeps the distribution balanced.
Work it out with a free tool
Copper weight changes how much current a trace carries
Going from 1 oz to 2 oz copper roughly halves the width a trace needs for the same current. Try both in the trace width calculator.
Compare copper weights