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I opened up my HP HDX laptop yesterday to clean it (Warranty was over 2 years ago), and to apply new thermal paste.

My laptop has only 1 fan, 2 sets of fins connected to 2 copper pieces to conduct heat. Around the graphics card, there are these really soft black rubber pieces stuck on the heatsink, and it makes contact with things like the memory modules of the graphics card, and some other parts. There's also this thicker light blue colored rubber piece between the northbridge and the heatsink.

The CPU and GPU chips use thermal paste, but I don't know what these rubber pieces do. Are they used as a substitute for thermal paste? There's a fairly large gap between the heatsink contacts and the chips without the rubber pieces so I figure that normal thermal paste won't work as well. There's no thermal paste between the rubber pieces and the parts it makes contact with. Would it be better to apply thermal paste to that?

  • GPU: 9600M GT overclocked when I play games, way underclocked when I'm not

  • CPU: Intel Core 2 Duo P7450 2.13 Ghz

  • GPU idle temp 49 C

  • CPU idle temp 39 C

Some people say these temps aren't high, but they are higher than when I bought the laptop (Also, currently in my area, humidex is around 35 - 42 C, around 27 - 30 C outside, 62% humidity. It's been so hot lately that some of my rubber bands melted into a sticky goop...)

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light blue colored rubber piece = Heat conductive rubber. Serves the same purpose as the thermal paste, with the idea it won't migrate out, dry out or develop voids like paste can do. –  Fiasco Labs Jul 14 '12 at 19:42
    
A photo would be helpful. –  Synetech Jul 14 '12 at 22:42

4 Answers 4

up vote 5 down vote accepted

The rubber pads are shims that prevent the components from touching or grating and they provide a little, soft support like a pillow, so that the components are not hanging in the middle of the air but also without having them bolted down. This is especially important for moving components like fans and hard-drives since having them hard-bolted to the chassis would create a lot of vibration and noise; having them sit on rubber shims absorbs the vibrations, creating quieter laptops. They are also insulators that prevent potential short-circuits. Do not apply the thermal paste to the rubber shims!

Yes, those idle temperatures are good and yes, it will be hotter than when you first bought it because the laptop now has a bunch of dust inside it which not only prevents airflow as well as a clean system, but also actively warms the system like a blanket. Unfortunately a fan is insufficient to keep the dust out because dust is mostly dead human skin which usually has oil and other stuff that makes it sticky, so simply blowing it won’t make it go away; it has to be wiped away.

It should come as no surprise that the ambient temperature has a big effect on a computer’s temperature. It may seem like electronics are only concerned with the temperature reading on the thermometer, not the humidex since they don’t sweat, except that humidity does indeed affect them, so yes, 35-42°C is going to make a computer run hotter.

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Yes there was a LOT of dust (They don't come of easily either 'cause they're greasy too. Managed to get them off yesterday). There's a drop where the heatsink uses thermal pads. How should I replace it with copper shims and thermal paste? Also, why would they use rubber? One of the rubber shims melted and stuck onto one of the modules... –  Alex Yan Jul 14 '12 at 19:45
    
When you say “thermal pad”, do you mean these? –  Synetech Jul 14 '12 at 19:49
    
Yes. I found that out later –  Alex Yan Jul 14 '12 at 19:52
    
There should only be a thermal interface material on the CPU and maybe on the GPU. Only apply a little thermal grease between the component to be cooled and the heatsink attached to it; nowhere else (nor too much). I assume you mean only the black rubber melted since as Fiasco said, the blue ones should transfer the heat. The black ones are not meant to take too much heat, so if it got too hot, then yes, they could melt just like how the CPU can burn if it gets too hot. Make sure the fan is working correctly and if your laptop has a fan vent on the bottom, don’t block it with your lap. ;-) –  Synetech Jul 14 '12 at 20:01

Its probably thermally conductive tape - such as this 3m stuff. As far as hardware goes it has a few advantages - its less messy than classic thermal compound, in theory is removable, and probably is easier to mechanically attack than standard heat sink compound. It also acts as a adhesive, so these parts usually arn't screwed down.

Without modification, replacing it with thermal compund may not work very well, since there's nothing holding these parts in place.

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Those "rubber" pads are not made from rubber. They are made from some eat conducting matter.
The goal is to replace replace thermal paste, because thermal paste only works if the surfaces are very flat.
With modern CPU, GPU and others, having a flat surface + thermal paste have a higher cost than irregular surface and rubber pad. The drawback of the rubber pad is it is less efficient to transmit eat to the eatsink (but it is worst with thermal paste + irregular surface).

Rule of thumb: never use/reuse a damaged rubber pad. Because the only advantage of a rubber pad is to stick to the entire surface in order to transmit the maximum eat. If it is damaged, less eat is transfered. So you have to flatted the surfaces (this is a long task) and apply thermal paste.

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So basically HP just spared themselves about $8 for every HDX? –  Alex Yan Jul 14 '12 at 20:25

As mentioned above those "rubber" pads are thermal pads. When you remove the heatsink those pads should be replaced because after a while they get the shape of the GPU and when removed and placed back again it is imposible to fit perfectly again. There is a product called K5-PRO which is actually a very gummy thermal paste and can replace thermal pads of up to 3mm thik. You can find it on ebay for around 6$ here http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item=261419411897

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