What? Isn’t that backwards? Technically, yes. The board is merely a pathway through which ICs talk to each other, and receive power to do so. However, if the power distribution network (PDN) of the board is inadequately designed, it can actually be heating up the ICs.
ICs are supposed to be the main source of heat on a PCB. Heat is conducted from the ICs to the board through their pins. Sometimes a metal slug or thermal glue is placed at the base of the component to enhance this effect. This method of component cooling is sufficient for most components. (The really power-hungry components will also require a heat sink to help cool them). So this means that the hottest locations on the board are right beneath the components. What is beneath the component? In the case of a BGA, there is usually a dense pinfield. This pinfield creates a web of copper which will choke the current feeding the IC. The current has to find its way through narrow pathways created by the “swiss cheese effect” of all the pinfield anitpads in the power and ground planes. These areas of high current density will start emitting power in the form of heat, which means a drop in voltage for the IC as well as additional heat in that area of the board.
This article discusses the problem in more detail:
Don’t heat up your ICs even more by designing an inadequate PDN.
How do you avoid that? Simulate it!