It is assumed that for normal design, the conductor surface area is relatively small compared to the adjacent free board area.
The amperage should be derated by 15 percent if the board thickness is 0.8mm or less, or if the copper thickness is 105um (3oz) or thicker.
For single conductor applications the chart may be used directly for determining conductor widths, conductor thickness and current carrying capacity for various temperature rises.
For groups of similar parallel conductors, if closely spaced, the temperature rise may be found by using an equivalent cross section and an equivalent current. The equivalent cross section is equal to the sum of the cross sections of the parallel conductors, and the equivalent current is the sum of the currents in the conductors.
The effect of heating due to components on the PCB is not taken into account in these charts.
For DC and low frequency AC applications, insulation, resistance, arc tracking resistance and flashover strength are important considerations.
In high frequency and microwave applications, important considerations are capacitance, dielectric constant and dissipation factor.
