Aight, I've been scowering a bit, but I want to get some definitive answers, hoping someone that's gutted their card already for LN2 or whatever can answer:
 
I'm specifically wanting to know the BACKSIDE/Backplate-side Thermal Pad sizes.  I know there are supposedly only pads on the VRAM on that side, I'm looking to get pads for the other areas - My guess is the vRAM is 1.5mm, which means I should get 2mm for the other areas, or is it 1mm on the chips & 1.5mm elsewhere?
 
Looking to further improve my heat dissipation following this crazyiness that the rest of the post will be.
 
Basic premise here is we tryin' to get them backplate/backside vRAM chips nice & cool, and reduce the other temps as a result - I think one of the primary reasons the 3090 FTW3 & other SKUs run as warm as they do is because of PCB heatsoak, which is even higher on the Kingpin because of it's thicker, gold-laced PCB, which is magnified by the vRAM chiplets being stacked on top of each other - adding heatsinks to those areas (since on most of the 3090 SKUs from eVGA I believe have thermal pads already present, maybe not the XC3s) can help.  Here is what I went through so far:
 
 
Inspecting nekkid PCB pics of the Kingpin to figure out WHERE to put stuff, without removing the backplate:
 

Sorry for the blurryness of these ones, they're not mine:


 
So the target areas of the backside, are basically these, you need to cover these areas, but on the backside:
 
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Which translates to, roughly: 

 
Now my first attempt was a cheap $11 set of Raspberry Pi-oriented heatsinks... I did not know they were so small, or I would not have ordered them:
 

 
The results from just that, with a fan blowing over them, however, were pretty impressive:
 

 
At this point I was like "Wowee, this actually works quiet well".  These temps are in an hour plus long gaming session in Cyberpunk 2077, at 5120 x 1440 with Ray Tracing fully cranked including the last setting being on "Psycho" - so pretty much the highest load I can throw at the card outside of Mining.
 
As you can see, the net drop in temps was already as little as 1C in some areas, but as much as 8.9C on one of the Memory iCX sensors!
 
I decided to go "overboard" and get more next, resulting in this look after some tinkering with the setup (I'll add a picture of what it currently looks like in a second post) :
 

 
And as expected, even with no thermal pads between the backplate & the VRM areas, we got further drops in temps, at the same settings in game in over an hour of playing again.  Here's a comparison of the original (no heatsinks) configuration vs what I'm running now:
 

We've now gone up to +1000MHz memory OC, and despite that higher clock, memory temps are 11.6C, 5.9C & 3.2C cooler respectively!
 
Feel free to post your own heatsink setups & results, I want this to be sort of a comparison of notes, and sharing of information type thread, for both 3090 XC3s, 3090 FTW3s & Kingpins... Throw in your non-eVGA 3090 too if you have one!

Next step is going to be getting thermal pads between the backside of the GPU die, and VRM areas, and the backplate... which I would love to know if anyone has any idea what size to get - I'm guessing it's .5mm thicker than the vRAM size, but not sure what exactly that size is on the Kingpin specifically, still 1.5mm or maybe 1mm?
 
Going to shut down & get a picture of the current heatsink layout, it's slightly different than the final layout pic in the above post - I adjusted them after looking at Buildzoid's PCB review & realizing the places I put the VRM heatsinks were kind of wrong.
 
EDIT: 
SCROLL DOWN FOR FTW3 & XC3 backside guide pics
 
Edit 2:
 
GUIDE TO KINGPIN LAYOUT & THERMAL PAD SIZES IN THIS POST LATER IN THE THREAD IF YOU WANT TO SKIP FORWARD: https://forums.evga.com/FindPost/3228558 

Some pictures of the current (probably final) layout:
 


 
And yes if you want maximum efficiency with the heatsinks, you definitely want a fan on them.
 
Links to the heatsinks (the black/newer ones), currently out of stock on Amazon I believe: https://smile.amazon.com/gp/product/B07BDKN3XV/
 
 

Whats your MEM temp during mining? Also which MEM readout is the backside?

anchang233
Whats your MEM temp during mining? Also which MEM readout is the backside?

I don't really do mining.  I tried it out previously, and the junction temp peaked at 82-84C during Ethereum mining.  That was with the first-try of the heatsinks (just the small silver ones) with a fan on it.  So I would assume they'd be slightly lower now.  Keep in mind, The Memory Junction Temp is always a fair bit warmer than the iCX Memory readouts, because (we think) the Junction Temp is from inside one of the memory chiplets, so it's an actual internal temp.
I would assume the hottest of the 3 temps are the backside vRAM (so Mem2) - it only makes sense, but I don't know that for sure.  I was really hoping Buildzoid would touch on it during his PCB analysis, but he didn't point out any of the iCX sensors on the Kingpin :(

Dabadger84

anchang233
Whats your MEM temp during mining? Also which MEM readout is the backside?

I don't really do mining.  I tried it out previously, and the junction temp peaked at 82-84C during Ethereum mining.  That was with the first-try of the heatsinks (just the small silver ones) with a fan on it.  So I would assume they'd be slightly lower now.  Keep in mind, The Memory Junction Temp is always a fair bit warmer than the iCX Memory readouts, because (we think) the Junction Temp is from inside one of the memory chiplets, so it's an actual internal temp.
I would assume the hottest of the 3 temps are the backside vRAM (so Mem2) - it only makes sense, but I don't know that for sure.  I was really hoping Buildzoid would touch on it during his PCB analysis, but he didn't point out any of the iCX sensors on the Kingpin :(

Hmm that's pretty good. The Strix/Gaming X Trio is at or above 90C according to HWINFO, FE is above 100C constantly, so that's pretty good improvement with the hybrid.
 

anchang233
 
Hmm that's pretty good. The Strix/Gaming X Trio is at or above 90C according to HWINFO, FE is above 100C constantly, so that's pretty good improvement with the hybrid.
 

I assume that's junction temp?  That's partly the Hybrid Cooler & partly the heatsinks, I had the first set of silver heatsinks on while doing that mining test to see what my temps/load wattage was like.

Dabadger84

anchang233
 
Hmm that's pretty good. The Strix/Gaming X Trio is at or above 90C according to HWINFO, FE is above 100C constantly, so that's pretty good improvement with the hybrid.
 

I assume that's junction temp?  That's partly the Hybrid Cooler & partly the heatsinks, I had the first set of silver heatsinks on while doing that mining test to see what my temps/load wattage was like.

Yeah junction temperature

So apparently backside vRAM thermal pads are supposed to be 2mm... I'm going to order 1mm (for the backside of the GPU die, I think that will be the right size), 2mm & 3mm, with a little 1.5mm as well just in case.
That's more than I planned on spending on the thermal pads, but at least I'll have a little bit of everything in case I need it.

Dabadger84
So apparently backside vRAM thermal pads are supposed to be 2mm... I'm going to order 1mm (for the backside of the GPU die, I think that will be the right size), 2mm & 3mm, with a little 1.5mm as well just in case.
That's more than I planned on spending on the thermal pads, but at least I'll have a little bit of everything in case I need it.

Which ones are the really good ones? Thermal grizzly is super expensive and I don't know the other brands very well.