Copper Thickness
The most common measurement unit for copper thickness on a Printed Circuit Board (PCB) is ounces (oz). How thick is that? It’s the thickness when 1 oz of copper
is spread evenly over a one foot square area. It equals 1.37 mils (or 1.37 thousands
of an inch). For other common units of measure, consider:
1 oz copper = 1.37 mils (thousands of an inch) or .00137 inch / 34.79 µm (micron
or micro meter)
For multiples of 1 oz copper, say 2 or 3 – just multiply above preferred unit of
measure by the desired multiple.
Generally, PCBs are fabricated with 1 oz copper thickness as a default, unless specified
otherwise. If a design requires more current carrying capability than 1 oz can handle,
increase the copper weight or width of the trace.
The thicker the copper, the higher the cost which is driven by the raw material
and processing costs. Recommended minimum spacing between copper features considering
copper weight guidelines are:
|
Cu Weight
|
Min Spacing
|
|
1 oz
|
3.5 mil (0.089 mm)
|
|
2 oz
|
8.0 mil (0.203 mm)
|
|
3 oz
|
10.0 mil (0.254 mm)
|
|
4 oz
|
14.0 mil (0.355 mm)
|
Tighter spacing is possible with engineering review. Follow the above as guidelines
only. In the long run, maximizing the space between copper features improves manufacturability,
and lowers cost.