Too much thermal grease?

So, I bought some arctic silver and applied a really thin layer onto my cpu/gpu. However, when I attached the heatsink back on and took it off to have a look if the heatsink touched the cpu/gpu, there was barely any thermal grease on the bottom of the heat sink in the area of CPU and none at the area of the GPU. (ie, the heatsink didn't even touch the GPU die)

So I added more thermal grease so that the heatsink touched the entire area of AS5 applied.

Is this a bad idea? Would the heatsink have deformed to come to contact with the cpu/gpu, anyway?

 

did it originally use a thermal pad and not paste?

 

for the gpu, yes, thermal pad. For the cpu, only half the thin layer of grease applied contacted the heatsink

 

The point of thermal grease is not to make the whole connection like a pad. It is to make the connection between the heatsink and the chip more efficient. If you had a thin layer applied to the chip and it squished out, that's a good thing. That means that there's a good interface between the heatsink and the chip.

Now, are you saying that the heatsink isn't making good contact with the chip? If so, yes, that is a very dangerous thing. Make sure that the chip is tight against the metal of the heatsink. The way you describe it though, I can't tell. Did the heatsink just squish out the excess thermal paste and make a good connection with the chip, or did the chip just not touch the heatsink at all? I can't tell from your description because you say it did both.

 

Firstly I would like the point out that my motherboard has one cpu chip, one core labelled nVidia, and some other core that has no labelling to the south of the nVidia labelled core. This unknown core is in contact with the heatsink by a thermal pad (which is quite thick). So I would assume that this is the GPU core?

Ok. I cleaned out the cpu/gpu cores and the bottom of the heatsink thoroughly.

When I applied a very thin layer of thermal grease, I re-attached the heatsink and screwed down all the bolts. Then I took out the heatsink again to check if the cores with the newly applied thin layer of grease actually touched the heatsink. The result is only half of the CPU core touched the heatsink, a corner of the nVidia core, and none of the unknown core was touched by the heatsink.

Worrying that the unknown (GPU?) core would not touch the heatsink at all with so little grease (since the thermal pad taken off was rather thick), I applied more on the unknown core. Then I thought I might as well just apply more on the CPU and nVidia chips to get full contact.

Now, after my final application, I screwed down the heatsink again, then took it off and looked at the bottom of my heatsink and all 3 chips left thermal grease on the heatsink. But none of the thermal grease spilled over the chips. Which means I applied enough to let it have full contact over the whole die.

Now, you bring up a point that the heatsink may not be fully and securely in touch with the chips. And that might be possible. I've already screwed down the heatsink firmly.

 

Not likely. The core labeled nVidia is the GPU. The other unlabeled one is probably the south bridge, responsible for all communications to PCIe devices and hard drives and such.

Hrm. Sounds scary. You should only ever need a very thin layer, so you may be stuck looking to get a thermal pad to replace it with, or some intermediary like a shim.

If you've screwed it down firmly and you still see a thick layer of thermal grease on top of the chips when you check, then do not turn the machine on. What you probably need are some copper shims so that the heatsink makes proper contact with the chips. You should see just the faintest film on the chip and the heatsink when applied properly.

 

Its not a good idea to put a thick coating of AS5 on any of the chips. If any of it squeezes out it can cause problems if it bridges two (or more) electrical paths. I would suggest using either copper shims or ICD7 in your situation.

 

I think the above sentence is pretty telling. It looks like the OP removed a thermal pad (thick) and are now expecting the heatsink material to directly contact the die of what sounds like the graphics chip. Obviously the original design allowed for a certain compression of the thermal pad, and now that it has been removed, there is no contact between the two. OP you need to put the thermal pad back in.

- Tim

 

Thermal paste is only meant to close the tiny gaps between the heatsink and chip. Therefore only a thin layer should be applied. Too much and it acts like insulation and it can actually trap more heat than it transfers to the heat sink.

 

what about for the cpu? is it ok that only half of the cpu's surface is in contact with the heatsink? And after I apply the thermal pad back on, should I still put grease on the Southbridge chip?

 

It's not the southbridge, it's the northbridge.

Anyway, if the cpu is only partially contacting the heatsink, that probably means that there was a thermal pad you removed there. I personally would readjust the heatsink, but you should place a copper shim between the cpu and heatsink. Do the same with the chip labeled nvidia. On both of these apply a very thin layer of thermal paste on both sides of the shim. Although shims are not optimal, they are better than thick thermal pads.

 

The cpu and nVidia chips had the thermal paste originally. Only the Northbridge one had thermal pad.

My main concern is, after I re-apply the thermal grease thinly and attach back the thermal pad, the chips don't fully touch the heatsink? I shouldn't need a shim because the heatsink didn't originally come with one, anyway.

 

You should ditch the thermal pad and use thermal paste only. That's my recommendation.

 

^ But that's granted that I use a copper shim to bridge the distance, yes?

I re-applied a thin layer of grease onto the CPU and GPU and then replaced the thermal pad onto the Northbridge for the time being. CPU temperatures now are 37 and 34. But the GPU idle temp is 64. Is this still too high? What would be the critical temperature for my GPU?

 

Critical temp for GPU varies somewhat, but generally speaking once you hit 80C, you're in trouble. If it's 64 at idle, it's almost certainly going to cause problems under load.

Reading through the thread, it sounds like you might have to go purchase new thermal pads and leave the grease alone. A "thin" application is a very relative term, but generally speaking, the thermal paste layer should be so thin you can see the metal of the heatsink right through it. Thermal paste is a gap-filler, nothing more. In an ideal world, both contact surfaces would be super smooth and no thermal paste would be necessary. But in the real world, the metal is full of microscopic nooks and crannies that severely hamper thermal transfer. If you're not getting the surfaces to mate fully, you're forcing all of the CPU's heat through that small contact patch. If the paste layer is opaque when you remove the HS, you're effectively adding insulation.

You could try using copper shims, but based on my assumption that you have limited experience with paste/heatsinks, that might cause more problems than before because you're adding another TIM layer, as well as the fact that it's very easy to get the thickness of the shim wrong without a very expensive caliper, risking damage to the chip and mobo. The CPU might be fine with a shim since many HS screws are spring-loaded to ensure even force distribution, but if the gap to the NB was that wide to begin with, you're going to have real issues getting the right fit.

 

That's why I put back the thermal pad for the NB. I'll let it settle a bit and then see what happens.

 

I wouldn't say you're damaging it at 80, but upwards over 80 is about as hot as you want it in a notebook.

 

I'm starting to have a feeling that my heatsink isn't contacting the chips properly. Like the heatsink isn't pressing down on the chips as hard as it should be to allow maximum thermal conduction. Maybe I'll try the method here: Increase contact b/w heatsink and gpu