Copper weight states copper thickness in ounces per square foot: 1 oz is about 35 micrometres (1.37 mils), half-ounce about 17.5 micrometres and 2 oz about 70 micrometres. Outer layers usually start as thinner foil and grow by plating, so 1 oz finished differs from 1 oz base. Heavier copper carries more current and spreads heat, but limits fine line and space because thick copper etches with more undercut.
Power layers need 2 ounce copper weight for the motor current, keep signal layers at half ounce or the 4 mil spaces won't etch.
Always say whether a copper weight is base or finished; plating on outer layers typically adds 25 micrometres or more.
Also heard as
- copper thickness
- oz copper
- foil weight
Related terms
Core
Fully cured laminate with copper on both sides, etched into inner layers and bonded with prepreg into a multilayer.
Etching
Chemical removal of unwanted copper from a board, leaving only the protected circuit pattern.
Plating
Electrochemical deposition of copper or other metals on a board, building hole walls and surface conductors.
Trace
Copper conductor path etched on a board layer, connecting pads, vias and planes.