you can read about thermal problem all over the place. I think there is an issue between Die and Heatspreader.
What else can cause that:
prime95 small FFT.. CPU temperature jumps instantly to 95°C and even after minutes the groundplate and heatpipes of my DarkRock pro 4 is not much warmer than my hand, where as the vrm heatsinks are twice the temperature i would guess. I reapplyed the cooler (with noctua nh1) as well as the stock cooler 5 times in total, with similar result. I realy dont want to delid my CPU, but i dont know what else can couse that behaviour other that bad contact to the heatspreader.
If the cooler would be hot as well this would be a total different thing, but it is not hot.
2x16gb cruical balistics
bequiet dark rock pro4
My 3900X gets to 86c here in AIDA64 with a H115i Pro with 2 extra fans and Liquid metal. (balanced AIO) 78c at turbo fans / pump.
There is a lot of heat concentrated in small spots (chiplets) and the heat density is quite high, so coolers cannot really cope as they could with normal CPUs.
The max limit of these is 95c. I'm against testing with Prime 95, that thing is just too aggressive. AIDA64 is much realistic.
Whatever ist running, if the temperature ist 90° for some time i expect the heatsink to become quite hot as well. But he does not.
So a 90° CPU and a 45° heatsink leads to my opinion that the heat transportation is inadequate or missdesigned.
Probably the soldering is of bad quality.... I don't know
It's as sacco says about density of chiplet and tiny surface area it has to contact the IHS. IHS is around 1406mm² while each chiplet is just 74mm² .