Question How much does cooling the underside of the motherboard/CPU typically help ?

[bit_user]

I have an Alder Lake N97 mini-ITX motherboard which has a soldered-down BGA CPU and non-standard heatsink. Upgrading the heatsink isn't a very realistic option, at least not without some custom machining that I'm not setup to do. I have added case fans, but the CPU is still sometimes pegged at the throttling temperature of 95 C, and that's before it's even gotten hot this summer (where I live).

So, my question is how much it might help for me to try various methods of cooling the underside of the motherboard/CPU? Is there any data on this, that people are aware of? Over the years, I've read claims that it's not uncommon for chips and components to dump heat into the motherboard, via their pins.

The system sits with the board in a vertical orientation. I'm considering putting a thin copper heatsink under the CPU, electrically insulated by a thermal pad.

 

[bit_user]

I've done a bit of it in the past and find it helps. It really depends on the motherboard though, and what they have on the backside of the CPU socket. When I have been able to, I've placed a 10cm x 10 cm aluminum heat sink on it with double sided thermal tape.

Thermal tape isn't very heat-conductive, to begin with, and that's assuming both surfaces are flat. In modern motherboards I've seen, there are lots of surface-mount components under the CPU, making a thermal pad the only realistic option. However, that creates a new challenge of how to hold it in place, which I chose to do simply by wedging it against the case.

I think this is a good opportunity for someone like Der8auer to work with motherboard & case makers to build boards with a bottom-side heatsink + mount and cases with an adequate cut-out and good backside airflow. A more thermally-conductive socket would also probably help.

It seems rather expensive to complete for very diminished returns compared to a few generations ago.

If you look at the trouble and expense people are going to with things like direct-die cooling and modified heatspreaders, it totally makes sense to me to look at backside cooling (in addition to, or instead of) that, for a few more degrees worth of improvement.

 

[mac_angel]

Thermal tape isn't very heat-conductive, to begin with, and that's assuming both surfaces are flat. In modern motherboards I've seen, there are lots of surface-mount components under the CPU, making a thermal pad the only realistic option. However, that creates a new challenge of how to hold it in place, which I chose to do simply by wedging it against the case.

I think this is a good opportunity for someone like Der8auer to work with motherboard & case makers to build boards with a bottom-side heatsink + mount and cases with an adequate cut-out and good backside airflow. A more thermally-conductive socket would also probably help.


If you look at the trouble and expense people are going to with things like direct-die cooling and modified heatspreaders, it totally makes sense to me to look at backside cooling (in addition to, or instead of) that, for a few more degrees worth of improvement.

the Z690 and Z790 (motherboards I've seen at least), the backplate is actually removeable. When you get the contact frame and dismantle the Intel mounting mechanism, the back part comes off as well. That can be replaced with a more solid, smoother back plate, and one that covers the whole back, and not leave out the middle rectangle like what's on motherboards. That gives you a larger, more fuller back plate, and it's between the motherboard and the new back plate that you would need good thermal pads. With that in mind, you'd be able to weld a much larger cooler directly onto that.

The thermal tape that I have is actually pretty good. I've had it for a few years and I've used it with the 10cm x 10cm aluminum heat sinks, connecting them to the back of GPUs, going back as far as my two 1080ti's. I now have them on the back of my 4090 (front side is waterblocked). They get pretty hot to touch, so the thermal tape, while might not be the greatest option, is definitely working.

 

[bit_user]

The thermal tape that I have is actually pretty good. I've had it for a few years and I've used it with the 10cm x 10cm aluminum heat sinks, connecting them to the back of GPUs, going back as far as my two 1080ti's. I now have them on the back of my 4090 (front side is waterblocked). They get pretty hot to touch, so the thermal tape, while might not be the greatest option, is definitely working.

Thermal tape is good for RAM cooling, chipsets, maybe VRMs... no argument there. I'm just saying you should compare the thermal conductivity of tape to that of half-decent heatsink compound. It's no contest.

Even good thermal pads tend to be more heat-conductive than tape, but thermal pads are also thick and that's a killer. If you need to move a lot of heat, like a CPU, even the 0.5 mm pads are too thick. That's why you should never use a thermal pad when any other solution would do. The Jetway board I'm dealing with originally shipped with a thermal pad under its heatsink/fan. Just replacing that with a good heatsink compound helped immensely! Before I did that, any workload would almost immediately hit 95 C.