When mounting power transistors and chips to a heat sink they often use
heat shrink grease to help dissipate the heat. Over the years I have
replaced or added this grease which I purchased at Radio Shack. One tube
lasted many years for the occasional times I needed it.

I dont need any right now, but I do not have any more on hand for the
next time i need it.

Anyhow, I understand this grease is pure 100% silicone grease. I've seen
it in both clear and white. I just tuned up my car and replaced the
plugs and wires. The auto parts store guy suggested using something
called "Spark Plug boot grease". It was only $3 and I know all too well
how plug wires tend to get stuck on the plugs and by the time I get them
off, I ripped off the terminal inside the boot. So, I bought and used
this grease. (which I know also repels moisture from getting into the
plug boots).

There is a lot left in the tube and I was just putting it away so I can
find it the next time I need it. I was reading the package and it says
100% pure silicone grease.

Hmmmm, wouldn't this be the same stuff used to mount semiconductors to
heat sinks? It sure does look the same too... If it's the same, I'll
have some for heat sink use too, and in that case, it gets put in with
my electronics repair stuff, rather than in my garage. I doubt it's
affected by cold weather, but keeping it in the house will keep it at
room temp all year long, rather than freezing in the garage in winter.

I thought I'd post this to see if anyone has used this for
semiconductors on heat sink, grease, or is there some reason NOT to use
this stuff for that purpose?

(If this is the same stuff, it's a heck of a lot cheaper to buy it at an
auto parts store).

On 12/04/2018 3:37 PM, wrote:
When mounting power transistors and chips to a heat sink they often use
heat shrink grease to help dissipate the heat. Over the years I have
replaced or added this grease which I purchased at Radio Shack. One tube
lasted many years for the occasional times I needed it.

I dont need any right now, but I do not have any more on hand for the
next time i need it.

Anyhow, I understand this grease is pure 100% silicone grease. I've seen
it in both clear and white. I just tuned up my car and replaced the
plugs and wires. The auto parts store guy suggested using something
called "Spark Plug boot grease". It was only $3 and I know all too well
how plug wires tend to get stuck on the plugs and by the time I get them
off, I ripped off the terminal inside the boot. So, I bought and used
this grease. (which I know also repels moisture from getting into the
plug boots).

There is a lot left in the tube and I was just putting it away so I can
find it the next time I need it. I was reading the package and it says
100% pure silicone grease.

Hmmmm, wouldn't this be the same stuff used to mount semiconductors to
heat sinks? It sure does look the same too... If it's the same, I'll
have some for heat sink use too, and in that case, it gets put in with
my electronics repair stuff, rather than in my garage. I doubt it's
affected by cold weather, but keeping it in the house will keep it at
room temp all year long, rather than freezing in the garage in winter.

I thought I'd post this to see if anyone has used this for
semiconductors on heat sink, grease, or is there some reason NOT to use
this stuff for that purpose?

(If this is the same stuff, it's a heck of a lot cheaper to buy it at an
auto parts store).


**It's not the same stuff. Heat sink grease, is not really grease. It is
a thermally conductive powder, suspended in a suitable medium, that
allows it to be spread on a semiconductor. Focus on the words:
"Thermally conductive".

I recall that clear stuff from the early 1970s. It is significantly
inferior to more modern products.

This will do the trick, at a reasonable price:

https://www.digikey.com.au/product-d...1011-ND/340309

Don't muck about, buy the correct stuff to do the job.

--
Trevor Wilson
www.rageaudio.com.au

On Thu, 12 Apr 2018 15:48:53 +1000, Trevor Wilson
wrote:

On 12/04/2018 3:37 PM, wrote:
When mounting power transistors and chips to a heat sink they often use
heat shrink grease to help dissipate the heat. Over the years I have
replaced or added this grease which I purchased at Radio Shack. One tube
lasted many years for the occasional times I needed it.

I dont need any right now, but I do not have any more on hand for the
next time i need it.

Anyhow, I understand this grease is pure 100% silicone grease. I've seen
it in both clear and white. I just tuned up my car and replaced the
plugs and wires. The auto parts store guy suggested using something
called "Spark Plug boot grease". It was only $3 and I know all too well
how plug wires tend to get stuck on the plugs and by the time I get them
off, I ripped off the terminal inside the boot. So, I bought and used
this grease. (which I know also repels moisture from getting into the
plug boots).

There is a lot left in the tube and I was just putting it away so I can
find it the next time I need it. I was reading the package and it says
100% pure silicone grease.

Hmmmm, wouldn't this be the same stuff used to mount semiconductors to
heat sinks? It sure does look the same too... If it's the same, I'll
have some for heat sink use too, and in that case, it gets put in with
my electronics repair stuff, rather than in my garage. I doubt it's
affected by cold weather, but keeping it in the house will keep it at
room temp all year long, rather than freezing in the garage in winter.

I thought I'd post this to see if anyone has used this for
semiconductors on heat sink, grease, or is there some reason NOT to use
this stuff for that purpose?

(If this is the same stuff, it's a heck of a lot cheaper to buy it at an
auto parts store).


**It's not the same stuff. Heat sink grease, is not really grease. It is
a thermally conductive powder, suspended in a suitable medium, that
allows it to be spread on a semiconductor. Focus on the words:
"Thermally conductive".

I recall that clear stuff from the early 1970s. It is significantly
inferior to more modern products.

This will do the trick, at a reasonable price:

https://www.digikey.com.au/product-d...1011-ND/340309

Don't muck about, buy the correct stuff to do the job.

I guess that answers this question.

Thanks for the speedy reply.

I kind of thought that there could be a special composition involved,
but I had to ask to find out.

Thanks again.

I like Dow 340. Also, do you know how to apply it ? You put a daub or a bead near or between the mounting screw(s) and tighten to squeeze out the excess. Spreading it can cause air pockets which defeats the purpose. This method prevents that.

You probably won't find a website that tells this method, but I know of what I speak. Just like you won't find on the web WHY to use 100 % ethylene glycol for your engine coolant, but I can make me case and it is hard to argue against. Anyone wants to dispute it make your case and then my case will bury you. Guaranteed.

You get sort of a feel for how big of a daub or bead to apply. Ideally it should stick slightly out the sides of the device, that assures full coverage. You don't want a huge amount of excess. Also in some cases it is a good idea to push the device on to the heatsink by hand with as much force as possible. Screws strip in aluminum and some of them have a spring type hold down.

The clear stuff is no good. Even the best stuff is actually a thermal insulator but it beats air. the white stuff has microscopic particles in suspension and they do most of the heat conduction. the clear stuff doesn't have it. Don't use it.

I like these:

https://www.digikey.com/product-deta...R171-ND/307793


Peter Wieck
Melrose Park, PA

On Thursday, 12 April 2018 06:38:19 UTC+1, wrote:

When mounting power transistors and chips to a heat sink they often use
heat shrink grease to help dissipate the heat. Over the years I have
replaced or added this grease which I purchased at Radio Shack. One tube
lasted many years for the occasional times I needed it.

I dont need any right now, but I do not have any more on hand for the
next time i need it.

Anyhow, I understand this grease is pure 100% silicone grease. I've seen
it in both clear and white. I just tuned up my car and replaced the
plugs and wires. The auto parts store guy suggested using something
called "Spark Plug boot grease". It was only $3 and I know all too well
how plug wires tend to get stuck on the plugs and by the time I get them
off, I ripped off the terminal inside the boot. So, I bought and used
this grease. (which I know also repels moisture from getting into the
plug boots).

There is a lot left in the tube and I was just putting it away so I can
find it the next time I need it. I was reading the package and it says
100% pure silicone grease.

Hmmmm, wouldn't this be the same stuff used to mount semiconductors to
heat sinks? It sure does look the same too... If it's the same, I'll
have some for heat sink use too, and in that case, it gets put in with
my electronics repair stuff, rather than in my garage. I doubt it's
affected by cold weather, but keeping it in the house will keep it at
room temp all year long, rather than freezing in the garage in winter.

I thought I'd post this to see if anyone has used this for
semiconductors on heat sink, grease, or is there some reason NOT to use
this stuff for that purpose?

(If this is the same stuff, it's a heck of a lot cheaper to buy it at an
auto parts store).

heatsink compound is grese loaded with zinc oxide powder. The ZO provides the thermal conductivity.

If you're stuck for some, toothpaste is surprisingly good. I tried it on a high diss AMD 8 core CPU, it only ran a couple of degrees hotter than the proper stuff.


NT

On Thursday, April 12, 2018 at 7:51:56 AM UTC-5, wrote:
I like these:

https://www.digikey.com/product-deta...R171-ND/307793


Peter Wieck
Melrose Park, PA

Are those the gray rubbery ones ? I like them, no goop required. One place I worked told us to use goop with them anyway, they were kind of anal about things.

On Thursday, April 12, 2018 at 6:06:05 AM UTC-7, wrote:
If you're stuck for some, toothpaste is surprisingly good. I tried it on a
high diss AMD 8 core CPU, it only ran a couple of degrees hotter than the
proper stuff.
If you need electrical insulation, petroleum jelly is probably better. The main objective is to fill the air gaps.

On Thursday, April 12, 2018 at 3:30:24 AM UTC-4, wrote:
I like Dow 340.


I've got several tubes of Dow 340. Very heavy per fluid oz; lots of solids. Expensive stuff but worth it.

On Thursday, 12 April 2018 14:35:16 UTC+1, wrote:
On Thursday, April 12, 2018 at 6:06:05 AM UTC-7, tabby wrote:
If you're stuck for some, toothpaste is surprisingly good. I tried it on a
high diss AMD 8 core CPU, it only ran a couple of degrees hotter than the
proper stuff.
If you need electrical insulation, petroleum jelly is probably better. The main objective is to fill the air gaps.

Petroleum jelly melts & runs.


NT

In article ,
says...

On Thursday, April 12, 2018 at 7:51:56 AM UTC-5, wrote:
I like these:

https://www.digikey.com/product-deta...R171-ND/307793


Peter Wieck
Melrose Park, PA

Are those the gray rubbery ones ? I like them, no goop required. One place I worked told us to use goop with them anyway, they were kind of anal about things.

The web page says they are pink; probably why Peter likes them!

Mike.

On 12/04/2018 08:30, wrote:

You probably won't find a website that tells this method, but I know of what I speak. Just like you won't find on the web WHY to use 100 % ethylene glycol for your engine coolant, but I can make me case and it is hard to argue against. Anyone wants to dispute it make your case and then my case will bury you. Guaranteed.

I remember when we had this argument at work after a certain automotive
TV program claimed the same.
We finally settled for 60% mix being better because the higher SHC over
100% ethylene glycol was preferred in a heat transfer system.
Knowing how marginal some automotive cooling systems are, I'd plump for
the 60% mix personally, even if there are other benefits to using 100%.

This was a few years back though, maybe newer coolants behave differently?

They are a very subtle shade of Dove Grey....

Peter Wieck
Melrose Park, PA

On Thu, 12 Apr 2018 00:37:18 -0500, wrote:

I thought I'd post this to see if anyone has used this for
semiconductors on heat sink, grease, or is there some reason NOT to use
this stuff for that purpose?

The best way to use thermal goo is to have the heat sink and device
touch each other with direct metal to metal contact, and with whatever
thermal goo you select filling in only the gaps. Making a thermal
sandwich with a thick layer of thermal goo which prevents direct
contact doesn't work very well. Idea is to grind flat and mirror
polish the heat sink and whatever is getting hot to get more metal to
metal contact, and use very little thermal goo. Some CPU's and video
chips have a mirror finish.

However, if you want to roll your own, diamonds are your best friend.
Here's a list of thermal conductivity of various compounds and
concoctions.
W/m*K
Diamond 1000
h-BN 600 (boron nitride)
c-BN 740 (boron nitride)
Silver 406
Copper 385
Gold 314
AlN 285 (aluminum nitride ceramic)
Aluminum 205
Graphite 200
Carbon 150
SiC 120 (silicon carbide)
Brass 109
ZnO 50 (zinc oxide)
Al2O3 25 (aluminum oxide ceramic)
TiO2 10 (titanium dioxide)

The common white thermal grease is zinc oxide, aluminum oxide, or
both. The expensive stuff adds boron nitride. The clear stuff is
just the grease, which is totally useless for thermal conduction but
might be a handy carrier if you want you mix your own using various
powders.

Tooth paste is the most common "alternative" thermal goo, although sun
screen which contains zinc oxide and perhaps titanium oxide should
also work.

If you can used and control a conductive thermal goo, try "liquid
metal", and alloy of bismuth and indium:
https://www.gamersnexus.net/guides/3064-intels-thermal-problem-pt1-liquid-metal-vs-thermal-paste-benchmarks-7900x
http://www.thermal-grizzly.com/en/products/26-conductonaut-en

Good luck.

--
Jeff Liebermann
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558

On Thu, 12 Apr 2018 00:30:20 -0700 (PDT), wrote:

I like Dow 340.

I have several tubes of the stuff. It works, but I prefer Arctic
Silver 5 for CPU overclocking and RF power devices. Actually, I
prefer lapping and polishing the device and heatsink, but that's not
always an option. A small tube of Arctic Silver 5 lasts me about 20
i7 size CPU's or about $0.25/per CPU because I use very little.

Also, do you know how to apply it? You put a daub or a bead
near or between the mounting screw(s) and tighten to squeeze out
the excess. Spreading it can cause air pockets which defeats the
purpose. This method prevents that.

That's not very compatible with my dictum "The less thermal goo you
use, the better it works". You want metal to metal as much as
possible with the thermal goo just filling in the cracks and gouges.

You probably won't find a website that tells this method, but I
know of what I speak. Just like you won't find on the web WHY
to use 100 % ethylene glycol for your engine coolant, but I
can make me case and it is hard to argue against. Anyone wants
to dispute it make your case and then my case will bury you.
Guaranteed.

I've posted my test results in sci.electronics.design. I'll see if I
can find the article. You might find it of interest.

You get sort of a feel for how big of a daub or bead to apply.
Ideally it should stick slightly out the sides of the device,
that assures full coverage. You don't want a huge amount of
excess. Also in some cases it is a good idea to push the device
on to the heatsink by hand with as much force as possible.
Screws strip in aluminum and some of them have a spring type
hold down.

Sigh.

The clear stuff is no good. Even the best stuff is actually a
thermal insulator but it beats air. the white stuff has microscopic
particles in suspension and they do most of the heat conduction.
the clear stuff doesn't have it. Don't use it.

At least we agree on that part.

--
Jeff Liebermann
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558

On Thu, 12 Apr 2018 10:16:55 -0700, Jeff Liebermann
wrote:

I've posted my test results in sci.electronics.design. I'll see if I
can find the article. You might find it of interest.

This should work:
https://groups.google.com/d/msg/sci.electronics.design/s_TJxYnypVk/1oSFPQdCBwAJ

A bit on tooth paste:
https://groups.google.com/d/msg/sci.electronics.design/s_TJxYnypVk/545qJWVLBwAJ

Using gold leaf:
https://groups.google.com/d/msg/sci.electronics.design/s_TJxYnypVk/yCgpwwtQBwAJ

Plenty more in that thread:

I found a more complete list of thermal conductivity:

W/m*K
Diamond 1000
c-BN 740 (Cubic Boron Nitride)
h-BN 600 (Hexagonal Boron Nitride)
Silver 406
Copper 385
Gold 314
AlN 285 (aluminum nitride ceramic)
Aluminum 205
Graphite 200
Carbon 150
SiC 120
Brass 109
Indium 86
ZnO 50 (zinc oxide)
Al2O3 25 (aluminum oxide ceramic)
Pastes 4.0
SilPad 2000 3.5
Circuit Works 1.84
Dow Corning 340 0.67

Note that most white thermal goo at the low end of the thermal
conductivity list with Dow Corning 340 in the really awful category.
Don't believe me? See:
http://www4.dowcorning.com/applications/search/products/details.aspx?prod=01015443&type=PROD
and look in the box under "properties".
Thermal Conductivity = 0.67 Watts per meter K


--
Jeff Liebermann
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558

On Thu, 12 Apr 2018 10:31:09 -0700, Jeff Liebermann
wrote:

On Thu, 12 Apr 2018 10:16:55 -0700, Jeff Liebermann
wrote:

I've posted my test results in sci.electronics.design. I'll see if I
can find the article. You might find it of interest.

This should work:
https://groups.google.com/d/msg/sci.electronics.design/s_TJxYnypVk/1oSFPQdCBwAJ

A bit on tooth paste:
https://groups.google.com/d/msg/sci.electronics.design/s_TJxYnypVk/545qJWVLBwAJ

Using gold leaf:
https://groups.google.com/d/msg/sci.electronics.design/s_TJxYnypVk/yCgpwwtQBwAJ

Plenty more in that thread:

I found a more complete list of thermal conductivity:

W/m*K
Diamond 1000
c-BN 740 (Cubic Boron Nitride)
h-BN 600 (Hexagonal Boron Nitride)
Silver 406
Copper 385
Gold 314
AlN 285 (aluminum nitride ceramic)
Aluminum 205
Graphite 200
Carbon 150
SiC 120
Brass 109
Indium 86
ZnO 50 (zinc oxide)
Al2O3 25 (aluminum oxide ceramic)
Pastes 4.0
SilPad 2000 3.5
Circuit Works 1.84
Dow Corning 340 0.67

Note that most white thermal goo at the low end of the thermal
conductivity list with Dow Corning 340 in the really awful category.
Don't believe me? See:
http://www4.dowcorning.com/applications/search/products/details.aspx?prod=01015443&type=PROD
and look in the box under "properties".
Thermal Conductivity = 0.67 Watts per meter K
I use some very fine particle size diamond lapping compounds in my
shop. Maybe I should consider using some for heat sink compound next
time I want to overclock the crap out of something. In fact, it could
first be used for lapping the parts and then just left in place.
Eric

On Thursday, April 12, 2018 at 1:17:00 PM UTC-4, Jeff Liebermann wrote:


You get sort of a feel for how big of a daub or bead to apply.
Ideally it should stick slightly out the sides of the device,
that assures full coverage. You don't want a huge amount of
excess. Also in some cases it is a good idea to push the device
on to the heatsink by hand with as much force as possible.
Screws strip in aluminum and some of them have a spring type
hold down.

Sigh.

Not sure where you disagree Jeff. Not speaking for the other Jeff (jurb), but I agree with him. If you get too much compound out of the sides, you've wasted it. If none appears you may not have put enough.

The idea is to squeeze as much out as is possible ensuring that only enough to fill gaps is left, on that we all agree. Forcing the device down by external pressure helps make sure any excess is forced out without relying on the devices own hardware to accomplish.

The center daub verses the even spread is debatable either way. RCA back in the late 60s told us to use the center daub and let it spread out on it's own. Their reason was to avoid air pockets. On small devices like transistors, that's what I do. On larger devices, I don't think enough pressure can be exerted to ensure a large area can force enough compound out of the joint, so I tend to carefully spread as thin a layer as I can accomplish.

On Thu, 12 Apr 2018 11:59:48 -0700, wrote:

I use some very fine particle size diamond lapping compounds in my
shop.

What's the grain diameter? If it's larger than the depth of the
cracks and crevasses in the aluminum extruded heat sink, then you're
taking a step backwards. The bulk of the heat is passed by metal to
metal contact.

Maybe I should consider using some for heat sink compound next
time I want to overclock the crap out of something. In fact, it could
first be used for lapping the parts and then just left in place.

As I vaguely recall, the typical flatness specs for extruded heat
sinks is something like 0.007 in/in. So, if the heat sink is 2 inches
wide, it can be warped 0.014" and still be considered usable. Ugh. It
will take an awfully large amount of heat sink goo to fill a 0.014"
gap.

The lack of flatness also causes problems when one tries to using such
a heat sink as a lapping plate. If the CPU can is softer than the
aluminum, it will convert the formerly flat can into a warped version
of the not very flat heat sink. I did stuff like this in the distant
past and found a really flat lapping plat to be a necessity.

If you want to see how bad it can get, take a black felt tip pen and
"paint" the top of the CPU or the heatsink black. Find a flat surface
(glass is good). Drop a sheet of fine emery cloth (2000 grit) on the
flat plate. Move the heat sink very slightly over the sand paper.
Inspect the heatsink. Where the heat sink was raised, the sandpaper
will remove the ink. Where there was a depression, the paint will
remain in place. Extra credit for repeating the test with a hot or
cold heat sink. Thermal expansion in an extrusion isn't uniform and
you will see bending in the heatsink.

There's also a problem with diamond dust and grease. While the grease
is great of keeping the diamond dust in place and making it easy to
apply, thermal cycling tends to pump the grease away from hot spots
leaving rather voids. You can sometimes see this when disassembling a
CPU and heatsink combination that has been running for a few years. If
you take it apart immediately after assembly, the thermal goo is
uniformly distributed (as long as the heat sink is reasonably flat).
However a few hundred thermal cycles later, it will have voids.

--
Jeff Liebermann
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558

On Thu, 12 Apr 2018 12:05:53 -0700 (PDT), John-Del
wrote:

On Thursday, April 12, 2018 at 1:17:00 PM UTC-4, Jeff Liebermann wrote:


You get sort of a feel for how big of a daub or bead to apply.
Ideally it should stick slightly out the sides of the device,
that assures full coverage. You don't want a huge amount of
excess. Also in some cases it is a good idea to push the device
on to the heatsink by hand with as much force as possible.
Screws strip in aluminum and some of them have a spring type
hold down.

Sigh.

Not sure where you disagree Jeff.

Sigh 2.0

Not speaking for the other Jeff (jurb), but I agree with him.

That makes three Jeff's. Nobody ever agrees with me, so you must be
referring to Jeff 1.0.

If you get too much compound out of the sides, you've wasted it.
If none appears you may not have put enough.

The idea is to squeeze as much out as is possible ensuring that
only enough to fill gaps is left, on that we all agree. Forcing
the device down by external pressure helps make sure any excess
is forced out without relying on the devices own hardware to
accomplish.

The center daub verses the even spread is debatable either way.
RCA back in the late 60s told us to use the center daub and let
it spread out on it's own. Their reason was to avoid air pockets.
On small devices like transistors, that's what I do. On larger
devices, I don't think enough pressure can be exerted to ensure
a large area can force enough compound out of the joint, so
I tend to carefully spread as thin a layer as I can accomplish.

As usual, I beg to differ:

1. If you apply enough pressure to make the thermal goo ooooze out
from the sandwich, you will either bend the device (as in a TO-3 or RF
power xsistor) or simply not be able to apply enough pressure with the
mounting screws and springs. I was going to calculate or measure the
pressure applied based on the recommended mounting screw torque for
various heat sinks, but don't have the time. I might have some time
this weekend to sandwich some Dow Corning 340 between two metal slabs
in an arbor press with a load cell and see what it really takes to
squeeze out the thermal goo. As you mention, I also suspect it will
be rather high pressure, far beyond what can be done with small
fasteners. Offhand, I would guess that this method was invented by a
thermal goo salesman in order to inspire users to consume more of his
company's thermal goo.

2. The problem with forming bubbles (voids) in the thermal goo was
originally mentioned in the literature in reference to removing the
heat sink after the thermal goo was applied. That will certainly
create bubbles. Somehow, someone extended that to the initial
application of thermal goo, which is not correct. I've never bothered
to prove this, so if you have time, try a blob of your favorite
thermal goo between two glass plates and look at it under a
microscope. If there are any bubbles, they should be obvious. If you
want, I can do this Friday as I have the necessary equipment:
http://802.11junk.com/jeffl/pics/microscopes/Olympus%20BH/slides/Olympus%20BH.html
3. Thermal goo is fairly cheap. However, it does make a mess when
the excess is squeezed out of the heat sink sandwich. I prefer not
cleaning up the mess.

My method of applying thermal go is fairly simple. Find the direction
on the heat sink in which the machining marks and gouges run. Apply a
tiny amount of thermal goo to the heat sink. Use a plastic razor
blade:
https://www.google.com/search?q=plastic+razor+blade&tbm=isch
to smear the thermal goo in the direction of ACROSS the machine marks.
The idea is to push the thermal goo into the grooves, crevasses, and
gouges in the heat sink. If the mating part of the sandwich also has
machine marks, do the same thing. The initial blob of thermal goo is
intentionally insufficient to cover the entire heat sink. Add small
blobs and continue to smear until the surface is covered. You will
see quite a bit of metal. That's good as you want metal to metal
contact. If there's any excess, wipe it off with the plastic razor.
When done, clamp it together and DON'T take it apart for "inspection".
If you do, start over by wiping the heat sink clean with alcohol, let
dry, and do the blob thing again. Thermal goo tends to harden as the
carrier evaporates. It will not flow into the cracks easily and will
resist compression. Best to start from scratch.



--
Jeff Liebermann
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558

On 4/12/18 10:05 PM, Jeff Liebermann wrote:
My method of applying thermal go is fairly simple. Find
the direction on the heat sink in which the machining marks
and gouges run. Apply a tiny amount of thermal goo to the
heat sink. Use a plastic razor blade:

As the original Jeff-1.0, I have to agree with Mr. Liebermann.

Originally, I was in the "blob and clamp" group. But, aside
from the mess that tends to make, I learned that really was
not the right method.

Of course, being the lazy **** I am, what I usually do is just
put a small blob on the part, smear it around with my fingertip
until I have a very thin layer spread over the entire part.
Then clamp it together. It may not be quite as right, but it's
a hell of a lot messy and I haven't had any overheating failures.

As in all things in life, there's a right way to do things, then
there's the internet, which will teach you all the other 101 ways
of doing it wrong.


--
"I am a river to my people."
Jeff-1.0
WA6FWi
http:foxsmercantile.com

"What's the grain diameter? If it's larger than the depth of the
cracks and crevasses in the aluminum extruded heat sink, then you're
taking a step backwards."

Now you're getting into the RMS finish left by the machines. In mass production I doubt it is very good. It is likely the grain is fine enough, in fact I have seen the results of machining on the surface and it looks like manufacturers are derating enough or just don't care.

"The bulk of the heat is passed by metal to
metal contact. "

Which is why I apply as much pressure as possible before tightening any screws. The strip, some devices are mounted by clips and the pressure depends on its modulus of elasticity. One advantage is that over time it presses continually and closes the gap, if any.

There is this pink **** out there that has such a high viscosity that I consider it unacceptable. It is hard to squeeze out of the damn tube, as such it would take so much force to actually get the high spots down to metal to metal contact that it would probably damage the device.

I have used tools to compress these, and I know when to stop. When you tighten the vise grips or whatever a little bit more and get no more goop then it is pretty much done. In the case of a large STK IC for example, I will take the old part and put it on top of the new part so it spreads the force and isn't likely to break the case. Squeeze the whole shebang until no more comes out.

As far as the compound and its additives, diamond dust is probably the best.. Copper beats aluminum or zinc oxide, but diamond blows their doors off. It also has a very good dielectric strength except for blue diamond. Apparently whatever "impurity" is in there causes it. I don' t feel like looking up what that is, feldspar or some **** ? Doesn't matter. Diamond does have a cost though, just how much is that semiconductor worth ?

"The lack of flatness also causes problems when one tries to using such a heat sink as a lapping plate. "

I wouldn't do that with a computer CPU. I have done it a few times with other devices and that was only so mush, I did not really remove any significant material. Truth is I was low on the "bird****" so I thinned it out a bit.. Beats nothing and the guy didn't want to wait.

Actually I have cleaned a bunch of them with coffee filters. They do remove some metal. In fact the did it to VCR heads as well, seeing that black on it was not dirt, it was aluminum. It is time to stop, but the heads were about as clean as they'll ever get, and it may have enhanced head to tape contact a bit. Just don't take off too much or there will be a bunch of wear and there goes your gap and azimuth offset sooner.

"If you want to see how bad it can get, take a black felt tip pen and "paint" the top of the CPU or the heatsink black. Find a flat surface (glass is good). Drop a sheet of fine emery cloth (2000 grit) on the flat plate. "

Actually the coffee filter should work.

That sounds like scraping. you know you have machines, and the ways are straight. Well those are cut on machine with straight ways so they are straight. And the ways for that machine are cut on a... this could go on forever. What is the FIRST reference ?

Scraped on plates. People actually scrape them by hand. they have a special surface on which the high spots are perfectly flat to withing a millionth of an inch, but there are valleys for oil. A roller will roll perfectly straight, or any guide that does not damage the plate. How to achieve this ?

They take two plates that are somewhat flat and blue them and put them together, where the bluing is not is a high spot so they take that down with the scraping tool. The two plates eventually seem flat, but they might not be.. One could be perfectly concave and the other convex to the exact same degree so they mate, but are not straight. So they have to use a third plate. you can't have a concave and a convex plate math another plate, it is simply impossible. And with hand tools they get them within millionths of an inch. I have watched them, and watched them sell them. Most companies do not need that accuracy but some do. they cannot tolerate a copy of a copy of a copy of a copy of flatness, they want the original. My friend makes the originals.

This is more accurate than polishing granite plates or even countertops. usually those are done with optical flats and/or light at an oblique angle, along with a good eye. I got a few sample from my late friend who did those granite and marble tops at his day job, other times he was a sculptor. I commissioned him to do one but he died so it is not done. i use those samples to process food, meat usually because we buy in bulk. not easy lugging a piece into the kitchen but it is worth the trouble, and I like to use on the occasions when I make a real pizza. All the pizza places around here just get worse and worse. They mostly suck or charge an arm and a leg.

"thermal cycling tends to pump the grease away from hot spots
leaving rather voids"

Hopefully those voids are where metal to metal contact was actually achieved. They are usually under spring pressure.

"Thermal expansion in an extrusion isn't uniform and
you will see bending in the heatsink. "

Mass production. I am surprised things work as well as they do. but all the mid fi audio amps are junk. Of course they want things to last two days past the warranty. One day is pushing it a bit too much.

On Thu, 12 Apr 2018 13:31:11 -0700, Jeff Liebermann
wrote:

What's the grain diameter? If it's larger than the depth of the
cracks and crevasses in the aluminum extruded heat sink, then you're
taking a step backwards. The bulk of the heat is passed by metal to
metal contact.

For power transistors, there is no metal to metal contact at all, if
there is a mica insulator in between the transistor and the heat sink.
Somehow that thermal paste transfers the heat thru that mica.

Going way back, I think my first encounter with power transistors were
the audio power output transistor in car radios. I remember working on
one and got that grease on my hands and I had to ask the teacher what
that was. He handed me a tube of it and told me to make sure the mica is
not cracked and make sure to apply enough of that grease so it oozes out
when I tighten the screws. Then he explained the purpose of it. That was
in the 1960s.

Since then, I've probably used more on CPUs than I ever did on
transistors. But the CPUs dont have an insulator on between.

On Thu, 12 Apr 2018 15:42:01 +0100, Lee wrote:


I remember when we had this argument at work after a certain automotive
TV program claimed the same.
We finally settled for 60% mix being better because the higher SHC over
100% ethylene glycol was preferred in a heat transfer system.
Knowing how marginal some automotive cooling systems are, I'd plump for
the 60% mix personally, even if there are other benefits to using 100%.

This was a few years back though, maybe newer coolants behave differently?

I dont know how this got into discussing Antifreeze, but you are
supposed to mix it 50-50. They claim that 100% antifreeze can freeze.
(Personally I have never seen it freeze). But I usually mix around 60%
AF and 40% water. I dont buy that premixed AF. The price is usually
about the same per gallon, so you're paying for water. That stuff is
made for people who are too lazy or stupid to mix it themselves...

"I dont know how this got into discussing Antifreeze,"

I mentioned it, but that was in another thread.

"but you are supposed to mix it 50-50. They claim that 100% antifreeze can freeze."

Whoever claimed that is an idiot. Don't listen to them. Actually anytihng can freeze, but that is not what they meant. The statement indicates they're totally unfamiliar with chemistry and physics.

"(Personally I have never seen it freeze). But I usually mix around 60% AF and 40% water. I dont buy that premixed AF. The price is usually about the same per gallon, so you're paying for water. That stuff is made for people who are too lazy or stupid to mix it themselves... "

It used to be that sex sells, now it is easy sells. This country and half the world is into easy, the easy way out. It has its costs.

As for antifreeze, if there is no water at all in there it is much less likely to form corrosive components. There is a difference in how it cools though, thus :

At the cylinder walls the heat gets intense enough to boil the antifreeze mixture and there will be a vapor pocket in between the coolant and the heat.. It does cool by evaporation some, but that also decomposes the ethylene glycol to some extent.

Though water has better thermal conductivity than ethylene glycol, that is offset by the higher boiling point which means that more of the coolant will be in contact with the heat. Conduction of the heat causes more even cooling than evaporation.

Also, the overall pressure in the cooling system is lower, resulting in less stress on all the sealing components as well as the hoses.

Since I started using pure antifreeze with no water I have never had a cooling system problem. Periodic flushes are unnecessary, look at it years later and it is still green, it never turns brown. It will never freeze in any environment in which you can survive, about 8.9F. It does not boil until 387F, much higher than water, which is what makes it cool better.

There is a car maker that uses pure polypropylene glycol as coolant in some models, don't recall which. It is highly hydrophilic so it is in a sealed system with no overflow or return. It boils at 381F and freezes at -74F. Another uses oil, though I am pretty sure it is not regular engine oil. the thermal conductivity is low so while it would not boil much, it would not remove as much heat and the localized pockets of it hot would probably cause breakdown. It may be a synthetic, I am not sure right now.

Another thing abut the lazy consumer, soem of them don't even read. First of all if they read the ingredients of the **** they buy to eat they wouldn't. But I think stores put the mixed coolant right with the pure antifreeze and people who don't pay attentyion just buy it because they see a slightly lower price. Lkke im a grocery store, you got "tastes like BUTTER", "can't beleive it's not BUTTER". Even paint, want oil based primer ? Look at the label carefully, many of them say "for OIL BASE", "to be used with OIL BASE" etc.

The money game. It keeps the stupidity contest on and people are winning all the time.

On Thu, 12 Apr 2018 22:34:41 -0500, Fox's Mercantile
wrote:

On 4/12/18 10:05 PM, Jeff Liebermann wrote:
My method of applying thermal go is fairly simple. Find
the direction on the heat sink in which the machining marks
and gouges run. Apply a tiny amount of thermal goo to the
heat sink. Use a plastic razor blade:

As the original Jeff-1.0, I have to agree with Mr. Liebermann.

Nobody agrees with me. Something must be wrong.

Originally, I was in the "blob and clamp" group. But, aside
from the mess that tends to make, I learned that really was
not the right method.

I should start posting photos of CPU heat sink installations on some
of the machines I've seen in my palatial office for repair. I'm now
buying alcohol by the gallon and Q-Tips by the Costco box.

Of course, being the lazy **** I am, what I usually do is just
put a small blob on the part, smear it around with my fingertip
until I have a very thin layer spread over the entire part.
Then clamp it together. It may not be quite as right, but it's
a hell of a lot messy and I haven't had any overheating failures.

Yeah, that works, except that the solvent used in some tubes of
thermal goo seems to remove the decals and painted letters on my
keyboards. I find it necessary to wash my hands after working with
thermal goo. Let's see what the MSDS says:
https://www.chempoint.com/products/download?grade=51854&type=msds
This is cute: Page 6:
Hazardous decomposition products
Thermal decompositions: Formaldehyde
That's odd. It's 50-70% zinc oxide, but the MSDS sheet does not
specify what the remaining 50-30% might be. No odor, so it might be
water, but that should be specified.

As in all things in life, there's a right way to do things, then
there's the internet, which will teach you all the other 101 ways
of doing it wrong.

Welcome to IoT, the Internet of Things (that are wrong). The best
part is that for every wrong way to do something, there are large
numbers of people (like me) who will blindly redistribute the wrong
way when asked. Things tend to look more authoritative when formatted
in HTML than with badly formatted ordinary text using broken English.
Never mind Fake News. Deal with the fake instructions crisis.



--
Jeff Liebermann
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558

Silicon pads. No thinking involved. No grease. No smear. Why not?

25 posts on the quantity of angels and pinheads involved. What a waste.

Peter Wieck
Melrose Park, PA

On Fri, 13 Apr 2018 08:25:20 -0700 (PDT), "
wrote:

Silicon pads. No thinking involved. No grease. No smear. Why not?

W/m*K
Diamond 1000
c-BN 740 (Cubic Boron Nitride)
h-BN 600 (Hexagonal Boron Nitride)
Silver 406
Copper 385
Gold 314
AlN 285 (aluminum nitride ceramic)
Aluminum 205
Graphite 200
Carbon 150
SiC 120
Brass 109
Indium 86
ZnO 50 (zinc oxide)
Al2O3 25 (aluminum oxide ceramic)
Pastes 4.0
Sil Pad 2000 3.5
Circuit Works 1.84
Dow Corning 340 0.67

Sil Pad 2000, which is one of the better silicon impregnated pads, has
a fairly lousy thermal conductivity. The big advantage is that they
don't use thermal goo:
http://www.henkel-adhesives.com/product-search-1554.htm?nodeid=8806349996033
For non-critical applications, such as those encountered by most of
those in this newsgroup, they're just fine. There are ways to install
them incorrectly. If they have a problem, it's that performance
varies with the amount of pressure applied.

25 posts on the quantity of angels and pinheads involved. What a waste.

Really? I got most of my experience with thermal management at a
company that made various RF power products. I think the biggest was
a 2-30MHz 1000 watt PEP power amplifier. To do that with BJT devices
required careful balancing of the devices used in Class AB, which
included careful mechanical balancing. To remain competitive, the
power products had to be better than the competition, while still
meeting FCC IMD specifications and without faking the numbers. The
competitive edge turned out to be the way heat was removed from the
devices, which was my headache. I had to go back to basics because
most of the applications engineers working for the heatsink and power
device companies were more than happy to make their life easier by
accepting mediocre performance. To get what I wanted, I had to start
with basics, and work my way up, which soon demonstrated that much of
the "no thinking" methods, and understandings of how things worked,
were wrong. I don't think it was a waste, but you might if you don't
have similar problems to deal with. Should that happen, be advised
that I derive considerable sadistic enjoyment watching others reinvent
the wheel.


--
Jeff Liebermann
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558

On Thu, 12 Apr 2018 13:31:11 -0700, Jeff Liebermann
wrote:

On Thu, 12 Apr 2018 11:59:48 -0700, wrote:

I use some very fine particle size diamond lapping compounds in my
shop.

What's the grain diameter? If it's larger than the depth of the
cracks and crevasses in the aluminum extruded heat sink, then you're
taking a step backwards. The bulk of the heat is passed by metal to
metal contact.

Smallest grain size is 1 micron. Or .0000039
Inches. My best surface plate is flat within 30 millionths of an
inch. My best set of gauge blocks, the ceramic ones, are +1 to + 3
millionths in size except for the 4 inch block which is +4 millionths.
Eric

Maybe I should consider using some for heat sink compound next
time I want to overclock the crap out of something. In fact, it could
first be used for lapping the parts and then just left in place.

As I vaguely recall, the typical flatness specs for extruded heat
sinks is something like 0.007 in/in. So, if the heat sink is 2 inches
wide, it can be warped 0.014" and still be considered usable. Ugh. It
will take an awfully large amount of heat sink goo to fill a 0.014"
gap.

The lack of flatness also causes problems when one tries to using such
a heat sink as a lapping plate. If the CPU can is softer than the
aluminum, it will convert the formerly flat can into a warped version
of the not very flat heat sink. I did stuff like this in the distant
past and found a really flat lapping plat to be a necessity.

If you want to see how bad it can get, take a black felt tip pen and
"paint" the top of the CPU or the heatsink black. Find a flat surface
(glass is good). Drop a sheet of fine emery cloth (2000 grit) on the
flat plate. Move the heat sink very slightly over the sand paper.
Inspect the heatsink. Where the heat sink was raised, the sandpaper
will remove the ink. Where there was a depression, the paint will
remain in place. Extra credit for repeating the test with a hot or
cold heat sink. Thermal expansion in an extrusion isn't uniform and
you will see bending in the heatsink.

There's also a problem with diamond dust and grease. While the grease
is great of keeping the diamond dust in place and making it easy to
apply, thermal cycling tends to pump the grease away from hot spots
leaving rather voids. You can sometimes see this when disassembling a
CPU and heatsink combination that has been running for a few years. If
you take it apart immediately after assembly, the thermal goo is
uniformly distributed (as long as the heat sink is reasonably flat).
However a few hundred thermal cycles later, it will have voids.

On Friday, April 13, 2018 at 12:13:21 PM UTC-4, Jeff Liebermann wrote:
Should that happen, be advised
that I derive considerable sadistic enjoyment watching others reinvent
the wheel.

Oh, you should, you should!

Horses for courses. Special applications require special attention - no surprise there.

Generally, when I "fix" something, I want it to stay that way. So, I will use (where appropriate) precision resistors, 105C+ caps, pre-screened film caps, matched transistors, dual-element fuses - again, where appropriate. The incremental cost across any one device will be less than the postage for that 'special' part and so forth. And, I also want to understand the 'why' of things. But I have no particular investment in being 'right', or even in being 'correct'. Just in the ultimate results.

Case-in-point - the relay for the HK Citation 17. After all the discussion, using the OEM relay just turned out to give a good result with no second thoughts or guesses. Good enough for me. Was it my only good option? Probably not. Was it -a- good option. Yes.

Peter Wieck
Melrose Park, PA

On Wednesday, April 11, 2018 at 10:38:19 PM UTC-7, wrote:
When mounting power transistors and chips to a heat sink they often use
heat shrink grease

That greasy stuff (also available in waxy and rubbery forms) is thermal transfer compound;
like a grease, but it is NOT grease.

It has to stay put in small crevices in order to work.

If you use a 'grease' formula instead of a 'thermal compound' formula, it might only
work for a few hours, then flow away.

If you try to add particles with high thermal conductivity to grease, you might
just be making spacers to keep the metal parts at a distance (it's distance times
resistance-to-heat-trasfer that you want to minimize). Don't fall for the 'better
conductivity' argument, it's conductivity DIVIDED BY GAP DISTANCE you care about.

On Fri, 13 Apr 2018 10:07:46 -0700 (PDT), "
wrote:

On Friday, April 13, 2018 at 12:13:21 PM UTC-4, Jeff Liebermann wrote:
Should that happen, be advised
that I derive considerable sadistic enjoyment watching others reinvent
the wheel.

Oh, you should, you should!

I do, I do. I positively salivate at the possibility of telling the
experts "I told you so".

Generally, when I "fix" something, I want it to stay that way.

Sure, if I can get the right parts. More commonly, I have a schedule
to meet and am forced to use not so wonderful parts. Using substitute
or recycled parts has caused me grief a few times, but in general, it
works because I understand how the circuit works and therefore what I
can get away with doing.

Incidentally, you can get diamond doped thermal goo:
https://www.innovationcooling.com/products/ic-diamond/
Not too expensive for those who want the very best at any price:
https://www.newegg.com/Product/ProductList.aspx?Submit=ENE&DEPA=0&Order=BESTMATCH &Description=ic+diamond

I also want to understand the 'why' of things.

Yep. If you re-read my long and boring rants on proper abuse of
thermal goo, you might notice that I spent quite a few bytes
explaining how things worked and why I do things in some particular
manner. While I believe that everyone is entitled to expressing their
opinions, I usually ignore the one-line "conversations" that have
become the defacto standard of chat type communications. Without
substantiation and explanation, opinions are worthless.

But I have no particular investment in being 'right', or even in
being 'correct'. Just in the ultimate resuts.

I have an investment in being (mostly) right. I value my reputation,
or at least what's left of it after making a few major screwups. If
"ultimate results" means doing whatever it takes to separate the
customer from their money, we need to have discussion on ethics.




--
Jeff Liebermann
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558

"I dont know how this got into discussing Antifreeze,"

I mentioned it, but that was in another thread.

"but you are supposed to mix it 50-50. They claim that 100% antifreeze can freeze."

Whoever claimed that is an idiot. Don't listen to them. Actually anytihng can freeze, but that is not what they meant. The statement indicates they're totally
unfamiliar with chemistry and physics.

I see a whole bunch of charts on the net, which show the freezing
temperature of various glycol-and-water mixtures.

For ethylene glycol, there's a very clear eutectic effect taking
place. The freezing point decreases from 0C to -50C, as the
concentration of EG in in the mix increases from 0% to about 65%. At
ratios above that (more than 65% EG, less than 35% water), the mixture
freezes at increasingly _higher_ temperatures. The freezing point of
100% ethylene glycol is shown as being around -20C, or not much "below
zero" Farenheit.

The curve for propylene glycol is very different. A mixture of PG and
water freezes at a few degress higher than an equivalent EG/water mix,
up to that magic 65% ratio... but the freezing point continues to drop
(slowly) all the way up to 100% PG. There's no visible eutectic
effect that I can see. However, the rate-of-decrease is quite low
above about 70% - going all the way up to 100% PG gains you only a
couple of degrees of increased freeze protection.

So, the question of "what's the right mix of antifreeze and water, for
the best freeze protection" depends very much on *WHICH* glycol is in
the antifreeze. I suspect a mixture of the two may have a more
complex behavior.

If you're starting with a 100% (or close to it) ethylene glycol
antifreeze, then the advice to stick to 50:50 looks very good, as far
as freeze protection is concerned. If you go up to straight 100%
glycol, you're good down to around -10F or -20C, but below that, the
glycol *will* freeze. You'd save money and have significantly better
freeze protection with 60:40 or 70:30.

If you're using propylene glycol, loading up to 80% or more won't hurt
your freeze protection... but it's still not as good protection as
you'd get with a 60:40 or 70:30 EG mixture.

As for antifreeze, if there is no water at all in there it is much less likely to form corrosive components. There is a difference in how it cools though, thus :

Keeping it absolutely dry is going to be difficult in practice. It's
going to absorb at least some moisture via the reserve tank, I
imagine.

On Fri, 13 Apr 2018 16:06:03 -0700, Jeff Liebermann
wrote:

Incidentally, you can get diamond doped thermal goo:
https://www.innovationcooling.com/products/ic-diamond/
Not too expensive for those who want the very best at any price:
https://www.newegg.com/Product/ProductList.aspx?Submit=ENE&DEPA=0&Order=BESTMATCH &Description=ic+diamond

Thermal Paste Application Methods - Which one is best? - The Workshop
https://www.youtube.com/watch?v=r2MEAnZ3swQ (10:13)
Included are various lines, an X, a P, finger smear, too much, too
little, etc. If you're impatient, skip to 7:49 for a Powerpoint chart
with the results.

--
Jeff Liebermann
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558

On Friday, April 13, 2018 at 7:06:19 PM UTC-4, Jeff Liebermann wrote:


But I have no particular investment in being 'right', or even in
being 'correct'. Just in the ultimate resuts.

I have an investment in being (mostly) right. I value my reputation,
or at least what's left of it after making a few major screwups. If
"ultimate results" means doing whatever it takes to separate the
customer from their money, we need to have discussion on ethics.

This is a hobby, not a business. I have yet to take any sort of compensation for anything other than parts for any repair (for a friend) I have ever made. As I do not make repairs for strangers, that is moot. I want the device to be safe, functional and reliable once it leaves my bench. Full Stop.

Peter Wieck
Melrose Park, PA

On Fri, 13 Apr 2018 15:57:55 -0700 (PDT), whit3rd
wrote:

That greasy stuff (also available in waxy and rubbery forms) is thermal transfer compound;
like a grease, but it is NOT grease.

Well, it's called thermal grease, silicon grease, high viscosity
semi-solid, or maybe magic grease. While not a lubricating
petrochemical compound, it is a type of grease.

It has to stay put in small crevices in order to work.

It also has to have a grain size small enough to fit in the crevices.
If you use a 'grease' formula instead of a 'thermal compound' formula, it might only
work for a few hours, then flow away.

Actually, it's worse than that. When heated, the viscosity of
commodity silicon grease is lowered, making it flow easier. It also
expands when heated. If I built a sandwich with a spring loaded heat
sink, some thermal goo, and a CPU, the expansion and easier flow will
cause the thermal goo to sloooowly ooooooze out of the sandwich. The
spring tension (as found in some CPU coolers) will help prevent air
gaps and thermal goo losses. Setting the spring pressure correctly is
tricky. If too little, the assembly will eventually rattle. If too
much pressure, and if too much thermal goo was added, it could
potentially make a mess. Fortunately, as the thermal goo slowly
ooooozes out from the sandwich with every thermal cycle, the gap
between the heatsink and the CPU slowly decreases, causing an
improvement in heat sink performance. That's why Arctic Silver and
others mention that you should see lower temperatures after the
thermal goo has had time to "break in" [1].
https://archive.techarp.com/showarticle600c.html

If you try to add particles with high thermal conductivity to grease, you might
just be making spacers to keep the metal parts at a distance (it's distance times
resistance-to-heat-trasfer that you want to minimize). Don't fall for the 'better
conductivity' argument, it's conductivity DIVIDED BY GAP DISTANCE you care about.

Yep. Actually, energy distribution is by the inverse square of the
distance, but at tiny distances, it might as well be linear. Having
too large a grain size will certainly ruin the thermal conductivity
but not because they don't fit in the cracks. It's because large
particles offer fewer points of contact between adjacent particles
than smaller (nano) particles:
Particle Radius Thermal Conductivity
50 micro meters 0.8 W/mK
1 micro meter 1.1 W/mK
0.003 micro meters 2.4 W/mK
I don't have numbers handy for the grain size used in commodity
thermal goo.


[1] http://www.arcticsilver.com/as5.htm
Due to the unique shape and sizes of the particles in Arctic Silver
5's conductive matrix, it will take a up to 200 hours and several
thermal cycles to achieve maximum particle to particle thermal
conduction and for the heatsink to CPU interface to reach maximum
conductivity. (This period will be longer in a system without a fan on
the heatsink or with a low speed fan on the heatsink.) On systems
measuring actual internal core temperatures via the CPU's internal
diode, the measured temperature will often drop 2C to 5C over this
"break-in" period. This break-in will occur during the normal use of
the computer as long as the computer is turned off from time to time
and the interface is allowed to cool to room temperature. Once the
break-in is complete, the computer can be left on if desired.




--
Jeff Liebermann
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558

On Fri, 13 Apr 2018 09:28:28 -0700, wrote:

On Thu, 12 Apr 2018 13:31:11 -0700, Jeff Liebermann
wrote:

On Thu, 12 Apr 2018 11:59:48 -0700, wrote:

I use some very fine particle size diamond lapping compounds in my
shop.

What's the grain diameter? If it's larger than the depth of the
cracks and crevasses in the aluminum extruded heat sink, then you're
taking a step backwards. The bulk of the heat is passed by metal to
metal contact.

Smallest grain size is 1 micron. Or .0000039 Inches

or 39 micro inches (one too many zeros).

My best surface plate is flat within 30 millionths of an
inch. My best set of gauge blocks, the ceramic ones, are +1 to + 3
millionths in size except for the 4 inch block which is +4 millionths.

Arctic Silver 5 uses:
http://www.arcticsilver.com/as5.htm
Average Particle Size: 0.49 micron or 0.000020 inch or 20 micro
inch. However, they use:
"Arctic Silver 5 uses three unique shapes and sizes of
pure silver particles to maximize particle-to-particle
contact area and thermal transfer."

Crystalline diamond nanoparticles have an advantage, where the flat
facet surfaces provide better thermal conduction than random, rough,
or spherical shapes.
https://www.google.com/search?q=diamond+nanoparticles&tbm=isch

Your diamond particles are twice the diameter, but considering the mix
of sizes in Arctic Silver 5, the sizes are comparable. They should
work if you decide to mix your own thermal goo. However, you can buy
diamond thermal paste:
https://www.innovationcooling.com/products/ic-diamond/
The data sheet claims:
Average Particle Size: 40 µ maximum particle diameter
40 micro what? inches or meters? Probably inches which is the same
as your lapping compound.

If we made CPU's and heat sinks with the same precision as your gauge
blocks, then we wouldn't need thermal paste or even mounting hardware.
The two surfaces would stick together by themselves.

--
Jeff Liebermann
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558

On Sat, 14 Apr 2018 11:54:58 -0700, Jeff Liebermann
wrote:

On Fri, 13 Apr 2018 09:28:28 -0700, wrote:

On Thu, 12 Apr 2018 13:31:11 -0700, Jeff Liebermann
wrote:

On Thu, 12 Apr 2018 11:59:48 -0700, wrote:

I use some very fine particle size diamond lapping compounds in my
shop.

What's the grain diameter? If it's larger than the depth of the
cracks and crevasses in the aluminum extruded heat sink, then you're
taking a step backwards. The bulk of the heat is passed by metal to
metal contact.

Smallest grain size is 1 micron. Or .0000039 Inches

or 39 micro inches (one too many zeros).

My best surface plate is flat within 30 millionths of an
inch. My best set of gauge blocks, the ceramic ones, are +1 to + 3
millionths in size except for the 4 inch block which is +4 millionths.

Arctic Silver 5 uses:
http://www.arcticsilver.com/as5.htm
Average Particle Size: 0.49 micron or 0.000020 inch or 20 micro
inch. However, they use:
"Arctic Silver 5 uses three unique shapes and sizes of
pure silver particles to maximize particle-to-particle
contact area and thermal transfer."

Crystalline diamond nanoparticles have an advantage, where the flat
facet surfaces provide better thermal conduction than random, rough,
or spherical shapes.
https://www.google.com/search?q=diamond+nanoparticles&tbm=isch

Your diamond particles are twice the diameter, but considering the mix
of sizes in Arctic Silver 5, the sizes are comparable. They should
work if you decide to mix your own thermal goo. However, you can buy
diamond thermal paste:
https://www.innovationcooling.com/products/ic-diamond/
The data sheet claims:
Average Particle Size: 40 µ maximum particle diameter
40 micro what? inches or meters? Probably inches which is the same
as your lapping compound.

If we made CPU's and heat sinks with the same precision as your gauge
blocks, then we wouldn't need thermal paste or even mounting hardware.
The two surfaces would stick together by themselves.
But they sure would be spendy. I don't even wanna remember what I paid
for my ceramic gage blocks.
Eric

Once upon a time on usenet wrote:
"What's the grain diameter? If it's larger than the depth of the
cracks and crevasses in the aluminum extruded heat sink, then you're
taking a step backwards."

Now you're getting into the RMS finish left by the machines. In mass
production I doubt it is very good. It is likely the grain is fine
enough, in fact I have seen the results of machining on the surface
and it looks like manufacturers are derating enough or just don't
care.

"The bulk of the heat is passed by metal to
metal contact. "

Which is why I apply as much pressure as possible before tightening
any screws. The strip, some devices are mounted by clips and the
pressure depends on its modulus of elasticity. One advantage is that
over time it presses continually and closes the gap, if any.

There is this pink **** out there that has such a high viscosity that
I consider it unacceptable. It is hard to squeeze out of the damn
tube, as such it would take so much force to actually get the high
spots down to metal to metal contact that it would probably damage
the device.

I have used tools to compress these, and I know when to stop. When
you tighten the vise grips or whatever a little bit more and get no
more goop then it is pretty much done. In the case of a large STK IC
for example, I will take the old part and put it on top of the new
part so it spreads the force and isn't likely to break the case.
Squeeze the whole shebang until no more comes out.

In my opinion you should never 'squeeze' it tighter than the clip / fastener
is going to hold it. Otherwise you squeeze too much out and are left with
voids.

As far as the compound and its additives, diamond dust is probably
the best. Copper beats aluminum or zinc oxide, but diamond blows
their doors off. It also has a very good dielectric strength except
for blue diamond. Apparently whatever "impurity" is in there causes
it. I don' t feel like looking up what that is, feldspar or some ****
? Doesn't matter. Diamond does have a cost though, just how much is
that semiconductor worth ?

"The lack of flatness also causes problems when one tries to using
such a heat sink as a lapping plate. "

I wouldn't do that with a computer CPU. I have done it a few times
with other devices and that was only so mush, I did not really remove
any significant material. Truth is I was low on the "bird****" so I
thinned it out a bit. Beats nothing and the guy didn't want to wait.

Actually I have cleaned a bunch of them with coffee filters. They do
remove some metal. In fact the did it to VCR heads as well, seeing
that black on it was not dirt, it was aluminum. It is time to stop,
but the heads were about as clean as they'll ever get, and it may
have enhanced head to tape contact a bit. Just don't take off too
much or there will be a bunch of wear and there goes your gap and
azimuth offset sooner.

"If you want to see how bad it can get, take a black felt tip pen
and "paint" the top of the CPU or the heatsink black. Find a flat
surface (glass is good). Drop a sheet of fine emery cloth (2000
grit) on the flat plate. "

Actually the coffee filter should work.

That sounds like scraping. you know you have machines, and the ways
are straight. Well those are cut on machine with straight ways so
they are straight. And the ways for that machine are cut on a... this
could go on forever. What is the FIRST reference ?

Scraped on plates. People actually scrape them by hand. they have a
special surface on which the high spots are perfectly flat to withing
a millionth of an inch, but there are valleys for oil. A roller will
roll perfectly straight, or any guide that does not damage the plate.
How to achieve this ?

They take two plates that are somewhat flat and blue them and put
them together, where the bluing is not is a high spot so they take
that down with the scraping tool. The two plates eventually seem
flat, but they might not be. One could be perfectly concave and the
other convex to the exact same degree so they mate, but are not
straight. So they have to use a third plate. you can't have a concave
and a convex plate math another plate, it is simply impossible. And
with hand tools they get them within millionths of an inch. I have
watched them, and watched them sell them. Most companies do not need
that accuracy but some do. they cannot tolerate a copy of a copy of a
copy of a copy of flatness, they want the original. My friend makes
the originals.

This is more accurate than polishing granite plates or even
countertops. usually those are done with optical flats and/or light
at an oblique angle, along with a good eye. I got a few sample from
my late friend who did those granite and marble tops at his day job,
other times he was a sculptor. I commissioned him to do one but he
died so it is not done. i use those samples to process food, meat
usually because we buy in bulk. not easy lugging a piece into the
kitchen but it is worth the trouble, and I like to use on the
occasions when I make a real pizza. All the pizza places around here
just get worse and worse. They mostly suck or charge an arm and a
leg.

"thermal cycling tends to pump the grease away from hot spots
leaving rather voids"

Hopefully those voids are where metal to metal contact was actually
achieved. They are usually under spring pressure.

No such luck. They're usually where there was little contact. Metal-to-metal
tends to stay that way duriung thermal cycling as long as pressure is
constant.

I've done a lot of work on laptops, a lot of them nasty to get into so it's
best to do it right first time. I've also lapped more than my share of CPU
'spreaders' (IHSs) and (desktop machine) heatsink bases.
--
Shaun.

"Humans will have advanced a long, long way when religious belief has a cozy
little classification in the DSM*."
David Melville (in r.a.s.f1)
(*Diagnostic and Statistical Manual of Mental Disorders)

"Thermal expansion in an extrusion isn't uniform and
you will see bending in the heatsink. "

Mass production. I am surprised things work as well as they do. but
all the mid fi audio amps are junk. Of course they want things to
last two days past the warranty. One day is pushing it a bit too
much.

"In my opinion you should never 'squeeze' it tighter than the clip / fastener is going to hold it. Otherwise you squeeze too much out and are left with voids. "

Disagree. What seem like voids are either the points of actual metal to metal contact or so close that you can't see the compound. Remember I said a bead or daub, if it is spread it is almost for sure not even and that will cause actual voids where it traps the air at the low spots of the compound. Some of those clips are too weak to overcome the viscosity of the compound, and some of that aluminum stuff they make the heatsinks out of is very soft and the screws might strip. The main thing is not to let it come up or move. If it is done right they are usually stuck pretty good though.

"I've done a lot of work on laptops, a lot of them nasty to get into so it's best to do it right first time."

Agreed, with anything. It's been said "How come there is never enough time to do it right but always enough time to to it again". I have even told people now and then "Hell no I don't want to do it right, I just don't want to do it again". I also don't want the liability, if the part fails guess what ?

"I've also lapped more than my share of CPU
'spreaders' (IHSs) and (desktop machine) heatsink bases. "

I haven't done that many processors in PCs, I just follow instructions. I did much work in power supplies and amps, unfortunately lapping is simply impossible on most. I also agree with Jeff Leiberman's caveat about making the surface concave. If you do that it could be worse than not lapping at all.. I only lapped in some output ICs once actually. I was extremely low on compound so I thinned out what was leftover and lapped with it. The ICs required no insulator being a totally plastic package. At the end of the lapping I had them in position and moved no more so that if there were any larger particles in there they would stay put, embedded and not keep the surfaces away. The only reason I was even able was because I was retrofitting a pair of LM3886 in place of a big STK and made a clip that went from one mounting screw to the other. I had plenty of room. (I would have put i pre outs and had the guy use an external power amp but the damn tone controls were in the global feedback loop)

Luckily I don't have to do much of that anymore or I would have a caulking gun full of compound like this one place I worked. Makes it easier to apply and I would never run out. They did but it took years even with a bunch of techs working.

I've been hearing of laptops with mo fan, and of course smartphones don't have them. Will it eventually get to the point where they don't need heatsinks ? Get an efficient enough switch and it could happen. I have already seen power switching transistors with no heat sink except the tab itself.

At 0 Vcesat, 0 Vceo, 0 Vbe, 0 tOFF and 0 tON there is no heat to sink.