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So what if thermal compound spreads?



 
 
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  #22  
Old April 11th 04, 07:39 PM
Matt
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Piotr Makley wrote:
"rstlne" wrote:


You don't say why it's inefficient !
Do you mean wasteful or something else constituting
inefficient. A vague and meaningless answer.


He means heat transfer will not be as good due to the large
gap between the core and the heatsink (I think large is a good
word because much of this is discuss'd on a "microscopic
level"




If the goo squishes out then presumably the layer of goo is no
thicker or thinner than if it didn't squish out?


Good answer.

  #24  
Old April 11th 04, 07:52 PM
baskitcaise
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Max wrote:

Which one?



I do know that artic silver 1 is slightly conductive, but the more worrying
thing is the capacitance if it gets too close to contacts.

http://www.arcticsilver.com/arctic_s...structions.htm

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Mark
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  #25  
Old April 11th 04, 07:58 PM
Matt
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CrackerJack wrote:
What exactly is the problem if too much cpu compound is put on the
core and it gets squashed out onto the surrounding area?

Apart from looking messy, is there any real problem with this?


I propose this answer:

1) If the compound is not too viscous, and the heatsink is clamped on
with some force, and you apply enough compound, the thickness of the
layer of compound does not depend on the amount applied, which is to say
that the excess gets squeezed out.

2) Thermal compounds are not electrically conductive.

3) Some thermal compounds (notably those containing silver compounds)
have capacitative properties that can be problemmatic if compound gets
between the chip's leads.

4) If you use a compound that doesn't have the problemmatic capacitative
properties and is not too viscous, in general it won't hurt to use too much.

  #26  
Old April 11th 04, 08:01 PM
Paul Hopwood
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Matt wrote:

I realised he could have meant either, so asked for
elaboration. Actually some thermal compund is electrically
conductive too,


Any of the stuff that's filled with metallic particles is potentially
electrically conductive.


Please name one.


Arctic Silver is capacitive, rather than conductive, but the same
applies in terms of application. Their instructions state:

"While much safer than electrically conductive silver and copper
greases, Arctic Silver should be kept away from electrical traces,
pins, and leads. While it is not electrically conductive, the compound
is slightly capacitive and could potentially cause problems if it
bridges two close-proximity electrical paths.)"

I wouldn't doubt there are other compounds around which are
electrically conductive.

--
iv Paul iv

  #27  
Old April 11th 04, 09:20 PM
Overlord
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On Sun, 11 Apr 2004 15:35:21 +0100, Piotr Makley wrote:

(John) wrote:

What exactly is the problem if too much cpu compound is put
on the core and it gets squashed out onto the surrounding
area?

Apart from looking messy, is there any real problem with
this?

Yes as it acts as an insulator. The idea of thermal compound
is to fill the very small scratches on the faces.


Actually the thermal paste is non-conductive. For maximum
heat transfer from the core to the heatsink, the two metal
pieces need to touch as much as possible. Hence, the addition
on the paste fills in the imperfections.

Other than being a mess, things should work just fine.



So something like a pinhead or two should be enough?

And a matchhead would be too much?


I've heard a grain of rice size is good. A matchhead should work.
I like to get single edged razor blades from the hardware to spread
it thinly and evenly. Think of frosting a cakeG.
I've even heard it said that you should even be able to almost read
the CPU die thru a thin haze of compound but given the wide range
of heatsink finishes, I would only go that thinly on a lapped HS.
Take your time and run it out evenly to all corners of the die.
Then at the last, try to run the razorblade all the way across from one
side to the other making a single unbroken even surface.

The Artic Silver people suggest rubbing compound into the base of the
heatsink, and then wiping it all off (NOT with alcohol!) with a cloth
before putting it straight down on top of the CPU (no twisting/slipping).
Supposedly it will imbed some of the compound in the "pores" of the
HS. Sounds like a good idea to me.
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  #29  
Old April 11th 04, 11:50 PM
Paul Hopwood
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Conor wrote:

Remember, the idea is NOT to form a layer between the two surfaces.
The purpose of the paste is to fill the valleys in the contact
surfaces with something which is more efficient at transferring heat
away from the CPU core than the air which would otherwise fill the
gaps


How I apply mine..


Small pea sized lump on the heatsink. Spread thinly then scrape off
with a razorblade.


Very small dot on the CPU core. Spread extremely thinly so it is hardly
visible.


I use a similar technique but use a bit less.

With the CPU fitted on the motherboard, I first apply a match head
sized dot to the top of the core and smear it around so it covers the
surface, then scrape most of it off with the edge of an old credit
card to leave very thin translucent layer covering the core.

I then clean the residue from the edge of the credit card with a ball
of cotton wool and use that to wipe the bottom the heatsink, just
sufficiently that it discolours the surface around where the core or
heat spreader will make contact, before fitting the cooler to the
board.

That way I use less compound and have cleaned my "applicator" in the
process; leaving just the cotton wool to discard. :-)

--
iv Paul iv

 




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