Why do you have to take care of the temperature of your PCB(while it is working)?
First of all because active electronic components (microcontrollers, memories, FPGAs, controllers for DC-DC converters) work correctly up to 85°C and in some cases up to 125°C. By this I am referring to the temperature indicated in the datasheets as Ta (it is the temperature of the environment in which the active component operates). Keep in mind that if your circuit board is placed in a metal box and there are parts that dissipate a lot of heat, sooner or later all this heat spreads throughout the PCB and as a result the “ambient” temperature will rise.
In addition to ambient temperature, another parameter to be considered for active components is the junction temperature Tj (junction temperature). The maximum junction temperature Tj typically varies between 125°C and 150°C. This parameter is specified in the section of the datasheet called “Absolute Maximim Ratings”
The “ambient” temperature and the maximum junction temperature are related by the formula
Tjmax=Ta+ Pd*Rth(j-a)
where Pd is the dissipation in W and Rth(j-a) is a coefficient that depends on the device package and on some layout tips (for example on how large is the copper area under the pad, on how many vias are placed under the pad).
Moreover. Consider that on extreme cases the track may catch fire or break.
OK, but what are the points to focus on in order to avoid overheating your circuit?
Proper sizing of your PCB traces. There are several calculators (generally based on the IPC-2152 standard). One of these is the Saturn PCB Toolkit which in addition to provide the trace width for a given current, also gives an estimate of the temperature rise. When you deal with high currents, you can both increase the trace width and order a PCB with a thicker copper thickness. However, ordering a PCB with a thicker copper may involve an higher cost.
