This is a PCB for a previous project that I did. (The circuit and the PCB's thumbnails are wrong, but when you click on 'open in editor', the correct circuit and PCB open.) For more details, check https://easyeda.com/prathikprashanth/pbl-sem-5-buck-linear-voltage-regulator

The exposed copper surfaces that you see are for heatsinking. Instead of using an actual heatsink, this is a good way of creating a 'PCB heaksink' and is typically done for surface mount components, but it can be done for through hole components as well, giving the circuit a low-profile look.

                                 ****Short circuit test****

                                   ****Scope Captures****