CPU thermal paste?

"~misfit~" said in :
JT wrote:
snip
I have a mate who's into electronics and I remember him using
"thermal transfer compound" on some of the transistors/heatsinks on
his home-made power amplifiers 20+ years ago. I don't kmow what it
was made of but I do remember him telling me it was really toxic.
Zinc oxide? That seems to ring a (faint) bell.

Zinc oxide is used as a filler in some low-grade thermal pastes. It is
not toxic. Zinc oxide is that water insoluable white stuff you see
painted on folks' noses to keep from getting sunburned.

"Zinc oxide is ideal for the nose and ears while swimming"
(http://www.healthcentral.com/mhc/top/001869.cfm).

I don't remember reading any warnings about not touching the stuff. In
fact, it usually needs to be reminded to users to NOT use their fingers
to spread around the paste because of the oil on their fingers.
However, I doubt any of the stuff is suitable for consumption (but
touching it is okay).

Maybe your friend was talking about a thermal adhesive because those do
use solvents that are toxic (but not in the dosage to which you would be
exposed for one heat sink, but maybe if you were on an assembly line).
I mean, hell, SuperGlue is toxic but I don't see folks keeling over that
accidentally got their fingers glued together. Acetone is toxic yet I
occasionally dampen a paper towel with it to remove some glue, residue,
or such, and my fingers are touching that Acetone wetted paper towel.
Grain alcohol is toxic, but are you going to give up your beer? If so,
I'll take it.

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*Vanguard* wrote:
"~misfit~" said in :
JT wrote:
snip
I have a mate who's into electronics and I remember him using
"thermal transfer compound" on some of the transistors/heatsinks on
his home-made power amplifiers 20+ years ago. I don't kmow what it
was made of but I do remember him telling me it was really toxic.
Zinc oxide? That seems to ring a (faint) bell.

Zinc oxide is used as a filler in some low-grade thermal pastes. It
is not toxic. Zinc oxide is that water insoluable white stuff you see
painted on folks' noses to keep from getting sunburned.

"Zinc oxide is ideal for the nose and ears while swimming"
(http://www.healthcentral.com/mhc/top/001869.cfm).

I don't remember reading any warnings about not touching the stuff.
In fact, it usually needs to be reminded to users to NOT use their
fingers to spread around the paste because of the oil on their
fingers. However, I doubt any of the stuff is suitable for
consumption (but touching it is okay).

Maybe your friend was talking about a thermal adhesive because those
do use solvents that are toxic (but not in the dosage to which you
would be exposed for one heat sink, but maybe if you were on an
assembly line). I mean, hell, SuperGlue is toxic but I don't see
folks keeling over that accidentally got their fingers glued
together. Acetone is toxic yet I occasionally dampen a paper towel
with it to remove some glue, residue, or such, and my fingers are
touching that Acetone wetted paper towel. Grain alcohol is toxic, but
are you going to give up your beer? If so, I'll take it.

Yeah. It obviously wasn't zinc oxide, that just jumped into my head. It was
some sort of metal oxide though I think. I remember he took great pains not
to get it on his skin and there was a red warning label on the tube warning
about transdermal absorbtion and toxicity. It wasn't an adhesive, it was a
thermal goop, to help heat-transfer. He used it 'tween the transistors and
the heatsink before he bolted them on. I still see him very occaisionally,
I'll ask him next time, I'm curious now. He's currently just about finished
making his own helicopter, completely home-made except for the rotors, he
saw those in someone's barn and got them for $20, then built a helicopter to
go with them. Single-seater, powered by a converted 120hp outboard motor
engine, the only other part of it he didn't build himself. (Although he made
an awesome exhaust manifold/extractor system for it which increased it's
power output considerably. It looks like a work of art, tuned according to
some arcane book he has on racing manifolds for two-stroke engines).
--
~misfit~

On Wed, 28 Apr 2004 21:23:26 +1200, "~misfit~"
wrote:

JT wrote:
On Tue, 27 Apr 2004 22:21:10 +1200, "~misfit~"
wrote:

WebWalker wrote:
On Mon, 26 Apr 2004 19:02:37 -0700, Ablang
wrote:

I just inherited a K6-2 300 Mhz computer, but the CPU fan &
heatsink keeps falling down off the CPU, which means that the
thermal paste is no longer sticking.

Thermal paste don't really sticky like glue and it is more like
toothpaste.

What you now know as thermal paste has only been around for a few
years. The early stuff was "sticky like glue", in fact it doubled as
glue as a lot of the HS's with this stuff didn't have clips.

Thermal "paste" has been around for ages. First used it the 60's for
some early transistor power amps. Has been used for years in the
electronics/computer industry. It was "discovered" for CPUs when the
heat started rising, and heatsinks started being needed.

Yep, I know that. I was talking specifically about the PC side of things. I
have a mate who's into electronics and I remember him using "thermal
transfer compound" on some of the transistors/heatsinks on his home-made
power amplifiers 20+ years ago. I don't kmow what it was made of but I do
remember him telling me it was really toxic. Zinc oxide? That seems to ring
a (faint) bell.

One of the best early ones was from 3M and used their newly developed
silicones. Still pretty much the standard for most applications.

JT

*Vanguard* wrote:

Oops, never mind. Did some searching to find the thermal conductance of
some metals, which are (along with some other materials):

Diamond = 1000 to 2600 W/mK (wow!)
Silver = 430 W/mK
Copper = 390 W/mK
Gold = 320 W/mK
Aluminum = 236 W/mK
Platinum = 70 W/mK
Glass = 1 W/mK
Air = 0.035 W/mK
Styrofoam = 0.03 W/mK

The above are for solid materials, not for pastes filled with micronized
filler using the above materials. Just imagine the cost for
diamond-filled thermal paste! Ouch.

Might not be too high. But using industrial grade diamond dust might
not be much better than silicone grease. Diamond's high conductance
relies on the alignment of its crystals, (as does its brilliance).
There is some work being done using "diamond like" layers on silicon
wafers used to fabricate CPUs. Could be a signifigant developement in
the ever increasing heat density of modern CPUs.

Virg Wall
--

It is vain to do with more
what can be done with fewer.
William of Occam.

On Wed, 28 Apr 2004 04:31:29 -0500, "*Vanguard*"
wrote:


Gold?

Hmm, just had a thought but no time to think it through. Silicone,
zinc, aluminum, and silver, in that order, give increasiningly better
heat transfer rates. Wouldn't gold be even better? But imagine the
price for gold-filled compounds!

Oops, never mind. Did some searching to find the thermal conductance of
some metals, which are (along with some other materials):

Diamond = 1000 to 2600 W/mK (wow!)
Silver = 430 W/mK
Copper = 390 W/mK
Gold = 320 W/mK
Aluminum = 236 W/mK
Platinum = 70 W/mK
Glass = 1 W/mK
Air = 0.035 W/mK
Styrofoam = 0.03 W/mK

The above are for solid materials, not for pastes filled with micronized
filler using the above materials. Just imagine the cost for
diamond-filled thermal paste! Ouch.

Gold might actually be a good alternative in the form of Gold Leaf.
Relatively inexpensive at hobby shops, and Gold leaf is one of the
thinnest, most malleable materials available. A sheet smoothed onto the top
of the processor would need no paste to hold it, would be soft enough to be
crushed into the little crevices and gaps, and has very good heat
conduction. Gold leaf is only a few atoms thick, so excess is unlikely.
Just have to make sure there was no extra that would overhang and short.
Will have to experiment with it when I get a chance.

JT

JT wrote:
On Wed, 28 Apr 2004 04:31:29 -0500, "*Vanguard*"
wrote:


Gold?

Hmm, just had a thought but no time to think it through. Silicone,
zinc, aluminum, and silver, in that order, give increasiningly better
heat transfer rates. Wouldn't gold be even better? But imagine the
price for gold-filled compounds!

Oops, never mind. Did some searching to find the thermal
conductance of some metals, which are (along with some other
materials):

Diamond = 1000 to 2600 W/mK (wow!)
Silver = 430 W/mK
Copper = 390 W/mK
Gold = 320 W/mK
Aluminum = 236 W/mK
Platinum = 70 W/mK
Glass = 1 W/mK
Air = 0.035 W/mK
Styrofoam = 0.03 W/mK

The above are for solid materials, not for pastes filled with
micronized filler using the above materials. Just imagine the cost
for diamond-filled thermal paste! Ouch.

Gold might actually be a good alternative in the form of Gold Leaf.
Relatively inexpensive at hobby shops, and Gold leaf is one of the
thinnest, most malleable materials available. A sheet smoothed onto
the top of the processor would need no paste to hold it, would be
soft enough to be crushed into the little crevices and gaps, and has
very good heat conduction. Gold leaf is only a few atoms thick, so
excess is unlikely. Just have to make sure there was no extra that
would overhang and short. Will have to experiment with it when I get
a chance.

As you said, it's just a few atoms thick. I think the 'sink and maybe the
CPU would have to be lapped.
--
~misfit~

On Thu, 29 Apr 2004 11:51:18 +1200, "~misfit~"
wrote:

JT wrote:
On Wed, 28 Apr 2004 04:31:29 -0500, "*Vanguard*"
wrote:


Gold?

Hmm, just had a thought but no time to think it through. Silicone,
zinc, aluminum, and silver, in that order, give increasiningly better
heat transfer rates. Wouldn't gold be even better? But imagine the
price for gold-filled compounds!

Oops, never mind. Did some searching to find the thermal
conductance of some metals, which are (along with some other
materials):

Diamond = 1000 to 2600 W/mK (wow!)
Silver = 430 W/mK
Copper = 390 W/mK
Gold = 320 W/mK
Aluminum = 236 W/mK
Platinum = 70 W/mK
Glass = 1 W/mK
Air = 0.035 W/mK
Styrofoam = 0.03 W/mK

The above are for solid materials, not for pastes filled with
micronized filler using the above materials. Just imagine the cost
for diamond-filled thermal paste! Ouch.

Gold might actually be a good alternative in the form of Gold Leaf.
Relatively inexpensive at hobby shops, and Gold leaf is one of the
thinnest, most malleable materials available. A sheet smoothed onto
the top of the processor would need no paste to hold it, would be
soft enough to be crushed into the little crevices and gaps, and has
very good heat conduction. Gold leaf is only a few atoms thick, so
excess is unlikely. Just have to make sure there was no extra that
would overhang and short. Will have to experiment with it when I get
a chance.

As you said, it's just a few atoms thick. I think the 'sink and maybe the
CPU would have to be lapped.

Of course lapped surfaces would be the best, or maybe use '2' sheets .
Hope I get a chance to try this soon. Can just see it now. Arctic Gold

JT

JT wrote:
On Thu, 29 Apr 2004 11:51:18 +1200, "~misfit~"
wrote:

JT wrote:
Gold might actually be a good alternative in the form of Gold Leaf.
Relatively inexpensive at hobby shops, and Gold leaf is one of the
thinnest, most malleable materials available. A sheet smoothed onto
the top of the processor would need no paste to hold it, would be
soft enough to be crushed into the little crevices and gaps, and has
very good heat conduction. Gold leaf is only a few atoms thick, so
excess is unlikely. Just have to make sure there was no extra that
would overhang and short. Will have to experiment with it when I get
a chance.

As you said, it's just a few atoms thick. I think the 'sink and
maybe the CPU would have to be lapped.

Of course lapped surfaces would be the best, or maybe use '2' sheets
. Hope I get a chance to try this soon. Can just see it now. Arctic
Gold

If you do I'd really like to know the results. I'm sure others would too.
--
~misfit~

"JT" said in s.com:
On Wed, 28 Apr 2004 04:31:29 -0500, "*Vanguard*"
wrote:


Gold?

Hmm, just had a thought but no time to think it through. Silicone,
zinc, aluminum, and silver, in that order, give increasiningly better
heat transfer rates. Wouldn't gold be even better? But imagine the
price for gold-filled compounds!

Oops, never mind. Did some searching to find the thermal
conductance of some metals, which are (along with some other
materials):

Diamond = 1000 to 2600 W/mK (wow!)
Silver = 430 W/mK
Copper = 390 W/mK
Gold = 320 W/mK
Aluminum = 236 W/mK
Platinum = 70 W/mK
Glass = 1 W/mK
Air = 0.035 W/mK
Styrofoam = 0.03 W/mK

The above are for solid materials, not for pastes filled with
micronized filler using the above materials. Just imagine the cost
for diamond-filled thermal paste! Ouch.

Gold might actually be a good alternative in the form of Gold Leaf.
Relatively inexpensive at hobby shops, and Gold leaf is one of the
thinnest, most malleable materials available. A sheet smoothed onto
the top of the processor would need no paste to hold it, would be
soft enough to be crushed into the little crevices and gaps, and has
very good heat conduction. Gold leaf is only a few atoms thick, so
excess is unlikely. Just have to make sure there was no extra that
would overhang and short. Will have to experiment with it when I get
a chance.

JT

I had actually thought of using gold leaf (several sheets) and
originally had it in my post about putting *pure* (24 karat) gold leaf
on the heatsink or on the CPU plate (smaller area) because it would be
soft and malleable. Maybe under pressure with the heatsink clipped onto
the CPU the gold leaf would mold into the cavities and microscopic pits.
But then I realized that what looks perfectly flat to your eye would
still probably end up with microcopically huge air bubbles, and while
malleable the gold would probably not ooze into the pits completely.
The only way it might work would be if there was a means of sending a
high electric current just through the gold leaf to flash melt it (to
minimize any generated heat that would conduct back to the CPU's die),
but I doubt the CPU die is electrically isolated from its heat plate,
and somehow I don't think consumers would have the necessary equipment.
Someone would have to find out if this idea worked and start a service
where users could get their selected heatsink flash fused with gold to
their CPU (or buy them that way as a package).

That's a bit of a dream at this time so I've started to look into the
Peltier cooling systems. I don't want to go with liquid cooling (which
still has a fan somewhere or else you listen to pumps and gurgles, have
to deal with leaks, and route all the plumbing [I like my innards very
neat]). ThermalTake has their SubZero solution but I don't like having
to surrender a PCI slot.
--
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"*Vanguard*" wrote in message ...

"do_not_spam_me" said in
om:

I have 2 old jars of Delta Bond thermal epoxy but haven't
used them, except when I needed a putty-like epoxy, and to
glue on heatsinks I've used only silicone rubber RTV,
except in the case of large heatsink and a small contact
area, where I used regular epoxy. Thermal epoxy for a
300 MHz K6-2 is an utter waste of money.

Silicone rubber to affix a heatsink? Geez, why not just
thermally isolate the heatsink with a thick rubber washer
and some contact cement?

I don't see how a rubber washer could affix a heatsink to a PC CPU,
and the only common high temperature rubber cement is disk brake
silencer (CRC makes it), which I don't like because it stains the
skin, and I don't know its thermal conductivity.

Why even bother affixing the heatsink at all?

Because even the worst heatsink and thermal adhesive will likely
improve the CPU package's thermal conductivity by a factor of 2-5.

It would be better to not use anything and just press the heatsink
and CPU together dry to get as much metal to metal contact as possible.

Unlikely, unless the surfaces match unusually well. Generally any
liquid will double the heat conductivity.

There's a reason no one includes silicon *rubber* in
their testing of thermal compounds in test reports, like
http://www.techwarelabs.com/reviews/...thermal_paste/ and
http://www.thetechzone.com/reviews/r...nd/index.shtml.
Silicone rubber is a thermal *insulator*, not a conductor. Yeah, it
transfers heat 4 times faster than air but that still sucks!

Where do those links list silicone rubber? The only silicone-based
thermal conductants I found there were made of silicone grease, which,
as you know, isn't like silicone rubber. Where does either mention
that silicone rubber transfers heat 4 times faster than air?

The thermal conductivities of some materials, in W/cm^2/cm/C
("Switching Regulators and Power Supplies," p. 112.):

silver 4.19
copper 4.01
gold 3.39
aluminum 2.25
beryllium oxide 2.08 (best of any electrical insulator, worse at high
temp)
silicon .83
iron .71
stainless steel .16 (type not specified)
Pyrex glass .010
mica .0043
epoxy laminate .0030 (circuit board material)
silicone rubber .0026 (GE brand, type not specified)
air .00024

Water is roughly 1/3 better than copper, oil about half as good as
aluminum, and diamond is much better than anthing, about 20
W/cm^2/cm/C.

This shows silicone rubber being over 10 times as good as air. The
thickness of the material also has to be considered because silicone
rubber insulators tend to perform better than mica insulators, even
when the latter are coated with thermal grease and the former are run
bare (http://users.ece.gatech.edu/~mleach/ or his old Audio magazine
articles). Also because any layer of glue, grease, or tape is so
thin, it's thermal conductivity isn't as important as the heatsink's
thermal resistance to the surrounding air (probably almost 1 C/W for a
Socket 7 heatsink).

Thermal transfer:
air ~ 0.035 W/mK
silicone rubber = 0.14 to 0.22 W/mK
3M thermal tape = 0.4 W/mK
silicone/zinc grease or paste = 0.4 to 0.9 W/mK
copper filled silicone grease = 2.0 W/mK
alumina (Artic or generic) = 4.0 W/mK
silver filled silicone grease = 4.2 W/mK
Artic Silver epoxy = 7.5 W/mk
Artic Silver 3 = 9.0 W/mK
Artic Silver 5 = 350,000 W/mK (claimed)

I don't see how Artic can claim their Silver 5 compound, a
*paste*, has a thermal transfer rate that is 814 times greater
than solid silver itself. When I Googled around, no one
actually tested this claim and instead just quotes Artic's own
specs. By the way, little known fact (well, it was to me until
now): there was no Artic Silver 4 because "4" in Japanese is
"shi" which means "death" (see
http://www.techaddicts.net/ArcticSilver5/AS5_1.html).

I don't know Japanese, but I thought one meaning of "shi" was the
number 4, as in ichi, ni, san, shi (1, 2, 3, 4).

What is the minimum W/mK or W/cm^2/cm/C for you to consider a material
to be a thermal conductor rather than a thermal insulator? Also
pre-formed sheets of silicone rubber has long been used to help cool
semiconductors, including in almost every computer power supply, so I
doubt that it's bad.

I was suggesting a cheap but adequate solution for attaching a
heatsink to a 300 MHz K6-2, for which the type of thermal glue used
will hardly matter, unless it's way too thick, and it's silly to take
extraordinary measures for such a CPU. In this case, "extraordinary"
means more than $2.