 Heavy copper layers are used for high current or to help dissipate heat.On the common FR-4 substrates, 1 oz copper per ft2 (35 µm) is the most common thickness; 2 oz (70 µm) and 0.5 oz (18 µm) thickness is often an option.Less common are 12 and 105 µm, 9 µm is sometimes available on some substrates.