Because power delivery throughout a CPU has been from top to bottom for decades (no idea why they went with this in the first place), Intel is working on inverting this and having power delivered from bottom to top and will see this realized in either their Arrowlake or later generation of Desktop CPU’s.
Potentially this inversion of power delivery will enable them to place the memory beneath everything and improve thermal characteristics.
Given everything has been evolution from discrete valve tubes onwards, so there is a lot of it just being the easiest way to provide the connection to the rest of the system in a manner that you can hand off easily to the motherboard designers to be cheaply and efficiently mounted.
ELI5,
why the cache/memory always seems to be on top of the processing chip, not bottom?
Because power delivery throughout a CPU has been from top to bottom for decades (no idea why they went with this in the first place), Intel is working on inverting this and having power delivered from bottom to top and will see this realized in either their Arrowlake or later generation of Desktop CPU’s.
Potentially this inversion of power delivery will enable them to place the memory beneath everything and improve thermal characteristics.
Given everything has been evolution from discrete valve tubes onwards, so there is a lot of it just being the easiest way to provide the connection to the rest of the system in a manner that you can hand off easily to the motherboard designers to be cheaply and efficiently mounted.
These are all in flip-chip packages. So no, power would come up through the bottom, and the transistors would be closest to the top.
Heat. The processor generates most of the heat, so you want the back side of the die somewhere a heat spreader can more or less directly connect to.
Well Top/Bottom is relative. But I assume you meant Top as in the side facing the heatsink.
Memory is “cooler” than dynamic logic, you want the colder element on top of the hotter one on the path of maximum dissipation.