The act of delidding goes back quite some time to when chip makers started putting the CPU die on top of the processor substrate (or package). Before then the die was under the substrate on the same side as the data pins and fairly well protected. By flipping the chip it allowed them more control over the size of the die and improved cooling. However, it also exposed the die damage due to incorrect heatsink mounting. There were several ways for chip makers to address this issue and the most common was by adding a heatspreader.

Early processors like the cartridge style Pentium II benefited from a delidding process because of the thermal compound used to connect the CPU to the cartridge. Replacing it was rather simple but required you to disassemble the cartridge. Modern CPUs like the Pentium 4 and Althon64 both came with copper based heatspreaders to protect the die and instead of using thermal paste they directly connected the die to the heatspreader using a soldering tekniq. It was so effective that delidding was no longer needed.