PCB Heat Sinking
There is no specific PCB area specifications cast on stone or that works outside the box all the time. However, there are design guidelines that address this concern: PCB heat sinks. PCB power components generate heat from themselves. This happens when current is passing through components that happen to have some resistance. This can be understood through an equation P = I2×R. The heat generated via this equation must be dissipated away from the PCB. Without a proper PCB Design mechanism, the components would get heated until they get destroyed. When designing a professional PCB, it is important to understand how the generated heat is distributed on the PCB. When the PCB prototype is powered and is in operation, thermal imaging can help to visualize how the heat is distributed in the PCB. This can then be helpful when doing a final design since one will be able to choose better locations for different components to ensure uniform heat distribution.
So when do you know that the heat sinks is sufficient?
One way of telling that the heat sink is sufficient is by ensuring that the PCB heat profile is similar throughout. A PCB thermal image can reveal how the heat is distributed in the whole system. A PCB is an anisotropic system. Naturally, heat would not be distributed uniformly. Another way is to generate a heat profile using a software right after designing the PCB and before prototyping. Software program such as HyperLynx can even generate a 3D PCB Model that will put into consideration the effect of change of component height and air flow on the PCB heat dissipation.
First, you want your PCB heat to be uniformly distributed for the good health of the PCB and to facilitate uniform heat sinking. The heat generating components must be positioned evenly throughout the board. Generally, to dissipate 1 watt of power, you need to have around 15cm2 board area for about 35◦C board temperature rise. To improve heat sinking on the board, thicker traces or copper pours can be used. PCB Assemblies such as Graphics cards and Motor Drivers need to dissipate lots of heat from one component. In this case, a heat sink is attached directly on the component.
In some cases, a Fan is also installed together with the heat sink to facilitate the flow of heat away from the PCB. Other techniques include using a number of screws with washers and also connecting the PCB with the chassis. Still, adding multiple vias when designing the PCB greatly improves the heat dissipation and distribution on the board.