Thermal pads in laptops

[Th3_uN1Qu3]

I want to hear your opinions on thermal pads used in laptops. I have heard people say things between "it's a bad idea to replace them with copper shims because they allow the chip to physically move with thermal expansion" and "they are absolute crap".

IMHO, i see thermal pads/rubber/sponges making sense on VRAM chips or a chipset without integrated graphics that dissipates 2-3W, but their usage on GPUs or IGPs with >10W power consumption and a die size of under 100mm^2 is simply retarded. It's the result of manufacturer cheapness, loose mechanical tolerances of the cooling system and planned obsolescence rather than any solid technical reason. Remember that pads, besides being less efficient at heat transfer than even the worst kind of paste, also age worse than paste, since there is physically more material.

The only way i would see a pad doing a reasonable job as thermal interface material for a GPU chip is if it has a large surface to dissipate into, before the heatpipe. This was the case for older laptops and it worked fine there (but also, they used to use leaded solder). Nowadays, with smaller, lower power chips that have just a thin flimsy piece of copper covering them (sometimes even aluminum), soldered to a small diameter heatpipe, using a thermal pad instead of building the heatsink tight enough to use paste seems like the worst possible idea to me.

It's not like it's hard to ensure adequate contact between the heatsink and die. I'm able to take an existing heatsink that used a thermal pad on the GPU or IGP and modify it for direct contact with the die and the use of paste by lightly bending it a couple times by hand and using nothing but my eyes and a little bit of paste for measurement. No shims required. If you're telling me the heatsink factory could not BUILD them like that from the get go, i'm not buying it.

The use of thermal pads doesn't only *seem* like it's a bad concept, it IS. I have solid proof and some cold hard numbers, some of which are downright scary.

Also, the whole "allows chip to physically move" idea is one of the stupidest things i've heard. Last time i checked, BGAs worked best when firmly attached to the board.

What is your take on this?

[SteveNielsen]

Re: Thermal pads in laptops

I agree with you. Thermal pads are a stupid idea. The chip movement idea sounds like hogwash too. Keep thermal expansion where it belongs, in bi-metalic strips.

[eccerr0r]

Re: Thermal pads in laptops

Always thought it was for assembly speed. A precoated thermal pad is faster to slap on than spreading heat sink compound and slathering it around hoping for no bubbles. The thermal pad is the same consistency from machine to machine, less chance of a failed machine that didn't get slathered properly.

[lezsimply]

Re: Thermal pads in laptops

I've seen someone here that uses copper tape with adhesive to replace thermal pads. However he does not like the idea of copper shim because heat is contained in a small area which does not dissipate at all. He modifies the copper tape to a point that it connects to the copper pipe that goes through the heatsink fins. I also like the idea but haven't tried it cause copper tape it expensive.

[Th3_uN1Qu3]

Re: Thermal pads in laptops

Always thought it was for assembly speed. A precoated thermal pad is faster to slap on than spreading heat sink compound and slathering it around hoping for no bubbles.

The CPU still has to use paste, so if they're doing it once, might as well squirt some on the other chip too...

[dellxps15]

Re: Thermal pads in laptops

for me it depends on the heat that chip release, some days ago i repaired a sony with a failed 216-0728018. after reball the chip, i put a thermal pad and idle temperature was 40°, so that chip temperature was low. different approach for bigger chip like 8600gt or 9600gt, there ill go for a copper shim that help to improve dissipation. there are also chip that have heatpipe not screwed on the bga, so a copper shim will probably be not the best option, while the soft thermal pad can help if heatsink move a bit up and down; a sample is a acer 5520g chipset.

it also depend on thermal pad quality. ive bought some of the cina and mine are a bit hard in component, so they hardly adjust to the perfect thickness required.

[Th3_uN1Qu3]

Re: Thermal pads in laptops

Idle temperatures are generally low on all modern chips due to advanced power saving technologies. It's the load temperature and variance between idle and load which matters. I agree that there are good thermal pads available, much better than what is applied stock at the factory - but even the best pad cannot touch even the worst paste possible, if there is good contact between the two surfaces.

For example, i have noticed that on high-end gaming laptops the GPUs generally run very hot under load, yet they fail less often than cheap ones. Same goes for desktop cards. And this is not due to build quality itself but thermal constraints - a big, power-hungry GPU must absolutely be securely fastened to a large copper surface with thermal paste, for heat to be efficiently removed from it. A large chunk of copper means thermal transitions will be slow, despite the GPU eventually reaching 90C or more, it does not go from cold and vice versa in a split second - it takes minutes, sometimes even 10s of minutes at full load to reach maximum temperature. Cooling happens a bit faster when load is removed due to the fact that the fan has spun up, but it is still a slow process. This helps keep the soldering and the chips alive.

If you do the same to a small laptop GPU, i'm sure it won't mind, either. I know it doesn't.

I have here a HP G62 with ATI HD5470 where i have done exactly this. I removed the pad then bent the heatpipe carefully for the copper "foot" soldered to the heatpipe to touch the GPU, and applied some MX-4. I left it to run FurMark all night, sitting on the floor, no cooling pad or anything. In the morning it was at just 72C, and it took almost 30 minutes for it to reach this temperature. It idles at 43. Also, there is always 5C or less temperature difference between the GPU and the CPU (they're on the same heatpipe), so the fan responds very well to GPU temperature changes despite it being controlled by the CPU temperature. This is simply unheard of for a stock one using the pad, even brand new. I'm sorry i didn't take pics but i was in a hurry and i need to return it to the owner now and get paid.

If the heatsink tends to move, you can stick a piece of conductive sponge under it like this:
so it is pressed in place by the case once you assemble the laptop. I have seen this done from the factory on some laptops. Now you know what that stuff is there for.

[dellxps15]

Re: Thermal pads in laptops

yes i know that sponge, but never searched them for new ones.

however most of the laptop failure are client bad usage of laptop. they put it on soft place, like bed.... or they never clean laptop from dust.

clean a laptop fan and use it on a linear place like a desk or table, will make it's life longer.

i have notebooks with 8600gt that runs fine from 2008.

[Th3_uN1Qu3]

Re: Thermal pads in laptops

however most of the laptop failure are client bad usage of laptop. they put it on soft place, like bed.... or they never clean laptop from dust.

Don't pull a nvidia and blame the user. It's not really like that. Some of them yes, but i've had laptops in for reballing that had just been cleaned and repasted a month or two before they failed.

[mockingbird]

Re: Thermal pads in laptops

There are thermal pads and then there are thermal pads. I wouldn't use the generic Chinese silicone pads. The problem I see with copper shims is that the cooling design or more specifically the contact between the heatsink and the chip is not specified with tight tolerances -- meaning, they're not perfectly true. With a shim, even if it looks like it's filling the gap to your naked eye, the pressure it not equal on all sides.

If I repair a laptop and the factory thermal pad is in pieces, I usually shop for a high quality replacement. I don't remember their names off hand, but there are a few manufacturers who make special pads designed specifically for this sort of application with a high W/mK.

[Th3_uN1Qu3]

Re: Thermal pads in laptops

With a shim, even if it looks like it's filling the gap to your naked eye, the pressure it not equal on all sides.

It doesn't matter, all heatsinks are uneven to some degree. This can easily be checked for by putting just a tiny bit of paste in the middle of the chip, and placing the heatsink. When the footprint paste leaves is uniform, the angle is correct. Then again, i no longer use shims, instead i bend the heatsink to fit like i just said. Even better than a shim, for free. Besides, a little pressure tends to hold the BGA in place better than a squishy pad, so it is also the pressure aspect besides just better heat removal.

If I repair a laptop and the factory thermal pad is in pieces, I usually shop for a high quality replacement. I don't remember their names off hand, but there are a few manufacturers who make special pads designed specifically for this sort of application with a high W/mK.

I know, but good pads tend to be not cheap and hard to find in some places, so you would have to keep stock. There is a review of the most popular types of pad compared to paste, but i can't seem to locate it now.

[magneh]

Re: Thermal pads in laptops

Hello!

Nice thread!

BTW, I'm waiting for some good quality thermal pads to arrive to clean and change them on a GTX460M of my Asus G53SW.

50MM x 50MM x 1.5MM Laird Technologies T-flex 760 Thermal

Here's the look of the cooler and graphics card when removed.

I'm going to clean it all with Isoprop. Alcohol and apply those thermal pads on memory chips and coils, and MX-4 on die.

It's a good and proper way to do it?
Wanna keep the beast fresh!

[dellxps15]

Re: Thermal pads in laptops

looking in the image..... if u have thermal compound on both cpu and gpu, i think 99% thatu dont need thermal pad in gpu. maybe some thermal pad on ram, but there is thermal compound also there, so be carefull that when thermal compound is applied, general no thermal pad are applied since thermal compound+ thermal pad = not good!!

[Th3_uN1Qu3]

Re: Thermal pads in laptops

He asked about the video RAM and said he will put MX-4 on the GPU. Yes, that needs thermal pads. It doesn't run too hot so pads will do, there is little point bothering with shims for that. BTW, MX-4 is the same paste i use and it is great.

[magneh]

Re: Thermal pads in laptops

looking in the image..... if u have thermal compound on both cpu and gpu, i think 99% thatu dont need thermal pad in gpu. maybe some thermal pad on ram, but there is thermal compound also there, so be carefull that when thermal compound is applied, general no thermal pad are applied since thermal compound+ thermal pad = not good!!

He asked about the video RAM and said he will put MX-4 on the GPU. Yes, that needs thermal pads. It doesn't run too hot so pads will do, there is little point bothering with shims for that. BTW, MX-4 is the same paste i use and it is great.

Hello and thanks for the inputs!

This is how the cooler came from factory. The coils of the GPU has thermal pads, gonna renew them.
The VRAM has thermal compound, gonna remove it and apply thermal pads.
On the GPU , I'm gonna put some MX4.

On cpu side, there are thermal pads for the coils, gonna change them also with new thermal pads , and MX4 on the die.