In power board design, heat is not just an unwanted side effect. It is part of the system behavior and needs a planned path, enough copper, and practical margin from the start.
See the thermal path early
If a hot component sits in the middle of the board with no clear thermal path to copper or the enclosure, a small heat sink later will not solve the problem. Good design often starts with package selection, copper area, and thermal vias.
Measure the prototype
Simulation helps, but real testing still decides the design. Keep a few temperature measurement points in the first prototype so decisions can be corrected with real data.