All the chips have pads/wires on the backside that are soldered to the boards they are attached to. As the chips get smaller, you can put only so many of these wires on the backside of the chip, limiting input/output/power. So, for RV770 with a 256-bit memory controller let's say you need 400 pins. On 55nm the size of the chip gives you enough space that you can fit all these 400 pins but if you keep the logic(transistor) count of the chip the same but shrink to 40nm, you will have much less physical space for these pins and may only be able to attach 300 pins. So this requires either a smaller memory controller or making the chip larger, ie adding more logic, to get enough surface area for all the pins.
I hope that all made sense
Originally Posted by [XC] gomeler
All the chips have pads/wires on the backside that are soldered to the boards they are attached to. As the chips get smaller, you can put only so many of these wires on the backside of the chip, limiting input/output/power. So, for RV770 with a 256-bit memory controller let's say you need 400 pins. On 55nm the size of the chip gives you enough space that you can fit all these 400 pins but if you keep the logic(transistor) count of the chip the same but shrink to 40nm, you will have much less physical space for these pins and may only be able to attach 300 pins. So this requires either a smaller memory controller or making the chip larger, ie adding more logic, to get enough surface area for all the pins.
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