CPU heatsink paste problem

Hi all,

The short version of the story is that I tried using a themal pad, such as the silicon sheet themal pads on my AMD CPU, the strange thing is with the themal pad (tried a few of um) the PC turns off after a second... using themal paste it boots up and runs fine... try the pads again same problem and it turns off after a second....

now I know these CPU's run hot, though It should at least get as far as to turn the monitor on or even get to the POST screen before it overheats and turns off.....

Now the themal pad *IS* connecting to the CPU AND HEATSINK so it sure has themal connection (and should be much better than the paste aswell) Though it just will not boot..... This makes no sence at all... I've always used paste on CPU's.... though over the pas 12 years or so doing electronics stuff ive always used pads, never had any problems and pads are much better than paste (IMHO). So I am now left very confused as it makes no sence.....

Even though I have been in electronics repair role for the past 12 years I am totally lost on this. Its like the CPU is "looking" for the paste and when it can't see it , it won't boot......

Very confused :-(

Chris

Reply to
exxos
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Possible, though I wouldnt think the CPU would last have lasted almost 2 years is it was faulty..... I will try on my g/f's PC, she has the exact same chip as me...

Chris

Reply to
exxos

Brands I ment.

been using them for 10 years, I think I get the hang of them ;-)

Chris

Reply to
exxos

Yes same cooler, I put the pad onto the CPU, put heatsink ontop, fixed all down..... PC turns off after 1 second, it does not even get as far as to turn the monitor on... take the CPU OUT and it actually stays on a few seconds before it turns off. but anyway..... I swapped back and forth between pads and paste about 20 times over today... in each case the pads didn't allow the PC to boot... The pad can't move and in no cases has it actually moved from where its supposed to be.... its pressing on the heatsink since you can see the mark on the copper where its been pressing... I thought it might be because the paste takes up more space and thus the gap may be greater and the pad may not be thick enough for it to contact on both.. but like I said its left a mark in each case so its contacting fine.... I even tried 2 and 3 pads ontop of each other and still the same problem...

Its all mounted on springs, I dont think you can actually mount it wrong. you cant apply too much pressure and you can't mount it at a angle or anything, I always check as best I can before power up...

True, though I dont know offhand what the thermal resistance of the paste is, but good pads are pretty low anyway, the problem of applying a even amount is not a problem with the pads. I've seen countless powersupplies fail down to not enough compound on the transistors, while im all for only using "whats needed" it tends to burn out and dry up very fast, so you have to use a lot more to make the thing last any amount of time. I am not sure what the paste life span is, I would expect it to last a fair amount of time, though in everything ive worked on from manufacture and own testing you have simply got to apply a pretty large amount. What I tend to do on power mosfets is just apply a blob and just push down and screw the thing, access splodges out the sides of course and makes a mess ( a lot of people will probably have something to say about that!), and you probably have far to much paste then, but applying less just isn't reliable. In fact I pretty much hate the compound now. I'm not saying which is better, in fact paste

*is* probably better IMO, though long term lasting I would go with the pads anyday. But anyway getting off the topic now....

My girlsfriends PC is overheating now, I applied on that "what was only needed" and I imagine there is nothing left of the paste now the same as was on my PC, my PC has been running hot for a while but this last week the CPU was hitting 57deg just with the PC doing nothing. There was still a thin layer of paste on my own CPU but just didn't work.... after I "blobbed" it on my CPU, its now running at 38deg idle with fan at full speed, about 41 at lowspeed (or 6V) 100% load at about 7V rises to 46deg.... all depends on fan speed really, but needless to say its pretty much shaved off 10deg from my CPU running temp.

I have to redo the gf's heatsink tomorrow, her's is now running idle at

57deg, I only built her PC a few months ago, thin layers of paste just does not work, it may work for a while but I have never seen it last more than a couple of years before it dries out.

BTW, its a AMD XP3200 400FSB CPU so it gets pretty hot under full load anyways..

I'm not trying to stat a themal war between which is better, though it would be interesting to hear about peoples experiences of paste vs pads.....

Though please remember I was asking to why the PC does not boot with pads and does with paste......

Chris

Reply to
exxos

You say it take a short time. Is it the _same_ cooler you try with pad and goop (paste) or is it two different? On some of the new intel's where the pins is in the socket, I've had the problem that some coolers have a uneven press or something, so that some pins don't make contact.

So try to ensure it is properly aligned, possibly change the brackets on the mainboard to the ones that (maybe) came with the cooler.

Besides, tests show that properly applied paste is better than pad ;) Because the pad is to thick... The paste should _only_ fill out scratches, not anything more.

--
MVH,
Vidar
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Reply to
Vidar Løkken

What do you mean by a few of them? I assume you don't mean several layers?

Are you sure they are thermal pads you have not double sided mounting tape of some sort?

Reply to
CWatters

You may have a defective chip. Some kind of internal intermittent crack has formed in one of the conductors. When you use a thicker silicon pad the heatsink clamp exerts more warping force on the chip activating the intermittent conductor. Try plugging in a chip without any heatsink. I bet that it may run longer than one second before it shuts down because of the heat buildup. I am not sure how safe this is.

Regards,

Boris Mohar

Got Knock? - see: Viatrack Printed Circuit Designs (among other things)

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Reply to
Boris Mohar

I use Arctic Silver paste, which I apply in a small drop, then drag a credit card over firmly, so it is only a thin film. Has worked great, even for _extreme_ overclocking. The el-cheapo pastes is no good, but if you buy a tube of artic silver it'll last for a good while, even tough there's only 10g in it.

El-Cheapo paste. I guess you compare your pads (which probably is very good pads) with cheap paste coming with the cooler.

Paste has always served me better at least...

--
MVH,
Vidar
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Reply to
Vidar Løkken

Intermittent fault can appear at any time.

Regards,

Boris Mohar

Got Knock? - see: Viatrack Printed Circuit Designs (among other things)

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Reply to
Boris Mohar

As it was explained to me in the 80's. Because the pads have some minimum thickness. The paste does not.

Surface to surface contact is best for thermal conduction. But surfaces are 'rough' they do not contact over their entire area, only in spots. The paste fills in the voids and is a better conductor than a void. The pads do not 'fill in' the voids as well and have some minimum thickness. That minimum thickness is greater with pads than with paste. Pads may have lower thermal resistance than paste, but they do not allow the surfaces to contact.

Ron

Reply to
TheTechnician

tape

Sorry. Couldn't see the diploma on your wall from here :-)

Reply to
CWatters

Nobody seems to have mentioned that many CPU pads these days are not pads as such but phase-change compound in a pad shape. They are one time use! The "pad" between heatsink and CPU flows when the CPU warms up. So they do fill gaps. The material phase changes (solid to liquid) when warm.

You can only use these pads once and you need to clean off the surfaces before fitting another if you change CPU.

--
Malcolm

 Malcolm Reeves BSc CEng MIEE MIRSE, Full Circuit Ltd, Chippenham, UK
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Reply to
Malcolm Reeves

Neither can I, they are filed away in "the great archives" *somewhere*.... probably mixed in with a pile of other junk.

Back from the gf's, her CPU did exactly the same as my setup, I have a spare MB, if CPU's wasn't so darn expensive id setup that and have a jolly good play in working out the results for it all...... assuming I could get pads to work which is still unsolved..... I always get the unsolvable PC problems :-(

Chris

Reply to
exxos

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