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Ridiculous? Backside cooling?

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Tekime

Member
Joined
May 12, 2003
Hi all!

Has anybody ever bothered to try cooling from the backside of a board; such as installing fans underneath hot spots like CPU, GPU, MOSFETS, northbridge, etc?

I've thought about throwing a fan on the back of my GF4 to spot cool the GPU from underneath, but I wonder if it will even have any impact. I don't have my DigiDoc5 back in yet, but I might try this out and if it helps at all consider some other spots.

Just wondering if this is a dumb idea I guess :) Is much heat ever able to radiate through a PCB anyway?

edit: Okay, the underside of this GPU has always gotten really hot, so I guess it's fairly obvious a good deal of heat is making it through.
 
Well you can plug in those exaust things in your pci slots....sooo, if you did this right under your graphics card it might cool a little. Thats the only thing I can think of.
 
It helps. I've seen a few pics of people's cards that have sandwhich cooling. How much it helps though is probably unknown. It could help you get those few extra mhz.
 
I have wondered about this myself, why not cool the back of the board right behind the cpu socket? It seems it would cool the board where it would be crucial. I am about to mod a pc up a little bit I might tryit out.
 
Yep it will normally give you a couple deg C or so. Works great. More if you can get direct access to the base of the board at the CPU.
 
..but the main reason why you could see a drop in temperature from cooling the backside of the MB, was that most boards then used an in socket thermistor. This can very easily be affected without the CPU actually getting any cooler.

But some airflow is always nice, but I think that where it help the most, is on your grachics card. After all, that's a chip soldered right to the board, not in a not-thermaly-conductive socket..
 
Hey, thanks for the replies! Hmm, I'm thinking a little more seriously about this now. I was going to cut the tray away behind my CPU and northbridge anyway, so I can easily add in temp sensors. Maybe I'll throw a few fans on there while I'm at it.

Now I just need a good way to attach a fan to the back of my video card. Too bad you couldn't get a heatsink on there, too.

I think I thought of this first when I was looking at this site:

http://homepage.ntlworld.com/bubo/

That's my board, and from the pics you would imagine there is enough heat radiating from the backside of the mobo that it's worth considering.
 
hmm, I don't think it would really help. Has anyone actualy seen drops from on die diodes? I know resistance in wires goes up with increased temps, but a couple C (the wires will surely cool, most likely not the core too much though) will not be anything huge. The heat problem is almsot exclusivly for transistors.
I honestly don't think you gain anything by doing this, I think time and materials would be better spent elsewhere.
 
All I know is my temps read lower so if the temp measureing device is cooler it stands to reason the the CPU is cooler also. By the same amount? who knows but the CPU is most certainly cooler. I think a couple deg C is significant personally.
 
climbski said:
All I know is my temps read lower so if the temp measureing device is cooler it stands to reason the the CPU is cooler also. By the same amount? who knows but the CPU is most certainly cooler. I think a couple deg C is significant personally.

not really, think about just cooling the sensor, not the source of the heat. if a house is on fire and the fire alarm goes off, would it be of much use to just provide fresh air to the alarm? would that turn the fire off when the alarm goes off? of course not. the insocket thermistors aren't really trustworthy as they are, the results get even more skewed when you cool the backside of it (thermistor is connected to the board, and in most cases doesn't even touch the cpu itself, so cooling of the back side of the motherboard mostly affects just the thermistor, so you just get nicer numbers).
 
While I can appreciate the scepticism I think I might give it a try anyway, at least on my GF4 to observe the effect. The underside of the GPU gets really, really warm, and I'm using a really good HSF on it as is. I'm also doing a vgpu mod which will probably kick my temps up even more.

Where is the best place to position a temp sensor? I'm thinking I can get a flat sensor under the heatsink, right against the edge of the GPU core. It wouldn't be affected directly by the additional fan, and while it might not be an accurate indicator of core temps I could read any differences that way.

While CPU might be ineffective since it is in a socket, I would imagine northbridge might be affected as well as gpu.
 
I really doubt this will work. If you cool the back of the mobo, all your doing is just that. Cooling the mobo. You might as well do it from the front where the actual heat is located. It may drop ( i doubt it though because you would need a nice fan to cool the mobo pcb) the socket temp, but then you're reading incorrect temps. If the mobo and chip didn't have the gap between them then i'm sure it'll help a tiny amount.
 
I couldn't find it but a guy a couple months ago had one of those heatguns and had pics of the temps all over the board. One pic he showed the back of the cpu socket area and it was just as hot as the front. Cooling this area could very well help stability.
 
wannaoc I posted a link to a site similar to what you mention a few posts back. I'm not concerned as much about the CPU as I am with GPU/NB. My reasoning is this -- if the back of the PCB is getting very hot, and I can move this heat away from the board it will have some impact on the chip itself.

I'll try to keep track of some temps and share my results with you guys.
 
well ive seen heat images of the back of mobos and pcb stuff and it is hot. some companies like winfast start to make "whole" heatsinks around the whole video card. kinda like that zalman video heat sink except with like 3 fans
 
It works. How much is whats debateable.

Heatsinks on the chips aren't the only path for heat to travel. You can also consider the copper circuit traces as secondary heat paths from the heat generating chips(as well as the circuit board itself to a lesser degree). Cooling these will in effect help draw heat from the chip itself. Deffinately not anywhere near effective as a heatsink on the actual chip, but it does help a bit. I've seen up to a few degrees difference personally.

Just feel the backside of a higher end video card, behind the GPU. Probably quite warm, even if you have decent cooling. Same goes for back of motherboard near CPU socket.
 
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