Keeping IC Packages Cool

Hard to do when the backside is all pins or pads.

But I do recall some serious overclockers having fans on the back of the mobo aimed at the socket and it's pins. But that was in,times just after breaking the 1GHz barrier.

It was more popular with GPU's and many modern day GPU's do have a heatsink on the back side of the board as well.

The board area under CPU is usually filled with ceramic capacitors, not to mention the lack of ecosystem support (i.e. CPU vendors just cannot rely on everyone starting to provide additional cooling from the other side, so they have to design for the most common denominator).

This method is sometimes used though, particularly with power transistors, where the heat conduction path through metal pads is usually better than the epoxy package over the die.

It's a fraction, yes, but it's also delayed a lot. For a while the challenge has not been to remove heat from the general area, but to keep small spots from overheating within milliseconds. Cooling on the other side of the building does not play a big enough role for it to matter.

(For enthusiasts, lowering environmental temperature would have the same effect.)

Next: we try to heat sink the sides of the CPU.

Nowadays GPUs do exactly that, they have thermal pads that connect the back of the PCB to a metal backplate. It is not clear whether this is actually necessary and not just for show.