Direct die cooling
Removing the CPU's metal lid (IHS) entirely and mounting the cooler directly against the silicon die. It removes two heat barriers (the lid's TIM and the lid itself) at once and can give dramatically lower temperatures — but it's risky and requires special brackets.
Idea: even with a soldered IHS and good paste there are a couple of heat steps between the die and the cooler. Direct die eliminates them by letting the cooler's cold plate sit directly against the silicon, often with liquid metal for the best contact. Win: large temperature drops (10-20+ °C) that allow higher boost/overclocking. Risks: without the IHS's protection the die can crack from the wrong mounting pressure, and it requires custom-made bracket frames and spacers. A classic extreme-enthusiast and record-chasing hobby; some manufacturers now sell direct-die blocks and frames. It goes a step further than delidding (which keeps but opens the IHS). Related to delidding and liquid metal.