Intel Core i9-9900K has a thicker die that hinders heat transfer

Computer enthusiasts begged Intel to start using solder again instead of TIM under the heatspreader of its processors, so a lot of folks were celebrating when news hit the web about the 9th Gen Core CPUs using solder. Unfortunately, it looks like despite the use of solder, chips like the Core i9-9900K are still running quite hot.

German overclocker der8auer investigated the matter and found that both the PCB and the CPU die are thicker with the Core i9-9900K versus the previous generation. This removes some of the benefit of the solder, as the thicker die hinders heat dissipation. Giving the die a good old fashioned lapping helps a lot to lower CPU temperatures, but this is not something that's easily achieved as there's significant risk that you damage the CPU.

Furthermore, der8auer illustrates you can also enhance the thermals by swapping the solder for liquid metal:

As it turns out, there are a few things involved here. For one, replacing sTIM with Thermal Grizzly Conductonaut (Der8auer has a financial interest in the company, but he does disclose it publicly) alone improves p95 average load temperatures across all eight cores by ~9 °C. This is to be expected given that the liquid metal has a vastly higher thermal conductivity than the various sTIM compositions used in the industry.

Via: TPU