Thermal relief

A typical pad on a printed circuit board is only connected to a few narrow tracks.

A pad directly connected to the copper pour is difficult to solder, since the heat quickly leaks away from the pad into the copper pour due to high thermal conductivity of copper.

A thermal connection restricts the heat flow, making the pad easier to solder.

Wire-leaded components may require the thermal relief pattern to be customized or even omitted when carrying radio-frequency currents (where the additional inductance would be problematic), or where very high current densities are expected (where the spokes of the thermal relief may act as a fuse).

In these cases the parts may require additional hand soldering during assembly.