Thermal conductive epoxy: powdered diamond, only $1200 for 5g

[Bill Beaty]

Never know when you might need some!

:)

Also gold conductive epoxy $425 5gm, probably better than
aquadag.

So, what's superior to the old JB-weld putty 500F deg? At work
we needed some high-temp epoxy for bonding sensors to copper
block stage heaters. I think we ended up using the stuff from
Atom, but here's my scratch collection for future ref:

http://staff.washington.edu/wbeaty/chem-epoxy.html

Omega has some cool stuff for cheap, a 1500F paste, zirconium
yttrium oxide powder (2-part, mixed with sodium silicate liquid.)
Sort of like expensive refractory plaster of paris, see YSZ:
https://en.wikipedia.org/wiki/Yttria-stabilized_zirconia
"Furnace cement" is similar and way less pricey, alumina mixed
with sodium silicate syrup.

Mystery cans from our storage, possibly YSZ paste:
Aerojet General 9-G coating, AMS-C199
can #1 gray powder, can #2 liquid (probably sodium silicate solution)



Hmm. Now I'm thinking DIY rubies? Made by dripping fused
material out of a small SiC crucible in a microwave oven? NASA
apparently likes to use SiC backed up with YSZ paste coating,
if the melt attacks the SiC.



(((((((((((((((((( ( ( ( ( (O) ) ) ) ) )))))))))))))))))))
William J. Beaty SCIENCE HOBBYIST website
billb at amasci com http://amasci.com
EE/programmer/sci-exhibits amateur science, hobby projects, sci fair
Seattle, WA 206-762-3818 unusual phenomena, tesla coils, weird sci

[whit3rd]

On Friday, December 11, 2015 at 7:11:35 PM UTC-8, Bill Beaty wrote:
> Never know when you might need some!

Seems a little high priced, to me. Abrasive graded grit in diamond
used to be up to $40/gram (last time I bought any). Epoxy, was
even cheaper.

> Hmm. Now I'm thinking DIY rubies? Made by dripping fused
> material out of a small SiC crucible in a microwave oven?

Or just buy 'em. Ten-millimeter round faceted will set you back
maybe 2 bucks each, after shipping
<http://www.gemsngems.com>

[Jeff Liebermann]

On Fri, 11 Dec 2015 19:45:09 -0800 (PST), whit3rd <whi...@gmail.com>
wrote:

Find a cheaper source. For 10 mm round they want $135/ea:
<http://www.gemsngems.com/product-category/lab-created-gemstones/hydrothermal-ruby/round-hydrothermal-ruby/>

However, you can get 10 mm ruby laser rods from Russia at reasonable
prices. Just slice, cut, and polish your own gems:
<http://www.ebay.com/itm/262112028186>


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

[John Larkin]

On Fri, 11 Dec 2015 19:45:09 -0800 (PST), whit3rd <whi...@gmail.com>
wrote:

The thing about particle-filled epoxy is the the particles increase
the gap, so increase thermal resistance. The particles are still
mostly separated by epoxy, a terrible thermal conductor.

Dow 340 silicone grease has very fine fill particles, and squishes
down somewhere below 100 micro-inches thickness with moderate
pressure. I bet that has lower theta than diamond-grit-filled epoxy,
given flat surfaces.

The price differential must be 1e4 or so.

[mixed nuts]

Cosmetic grade Boron Nitride is pretty cheap and very fine. Plus, it'll
hide your wrinkles.

--
Grizzly h.

[John Larkin]

The best particles are no particles. But if the surfaces aren't
super-flat, fill is needed, so something with very small particles
will help. It's important that it flow out of the contact areas into
the gaps.

Given a typical power mosfet (very flat) and a typical extruded heat
sink (not very flat) Dow 340 will cut theta by a factor of 3 or so.
I'm guessing (pat pending) that diamond-grit goop wouldn't be
dramatically better.

[whit3rd]

On Saturday, December 12, 2015 at 10:13:06 AM UTC-8, Jeff Liebermann wrote:
> On Fri, 11 Dec 2015 19:45:09 -0800 (PST), whit3rd <whi...@gmail.com>
> wrote:

[about growing rubies]

> >Or just buy 'em. Ten-millimeter round faceted will set you back
> >maybe 2 bucks each, after shipping
> ><http://www.gemsngems.com>
>
> Find a cheaper source. For 10 mm round they want $135/ea:
> <http://www.gemsngems.com/product-category/lab-created-gemstones/hydrothermal-ruby/round-hydrothermal-ruby/>

There's multiple processes and recipes; I was looking at a less expensive variant:
<http://www.gemsngems.com/product-category/lab-created-corundum/lab-created-ruby-5/round-lab-created-ruby-5/>

[Phil Hobbs]

The problem with grease is that it tends to pump itself out from under
the hot spots under temperature cycling. If one could get the diamond
particles to embed themselves in both sides of the metal, they'd stay
put and probably improve the theta.

Cheers

Phil HObbs

--
Dr Philip C D Hobbs
Principal Consultant
ElectroOptical Innovations LLC
Optics, Electro-optics, Photonics, Analog Electronics

160 North State Road #203
Briarcliff Manor NY 10510

hobbs at electrooptical dot net
http://electrooptical.net

[mixed nuts]

I think that's correct - the grease would have to be very heavily loaded
and under extremely high clamping force to embed the particles and make
a dramatic difference.

Most of the greases and thermal (not electrically conductive) adhesives
are filled with hexagonal Boron Nitride and/or Aluminum Nitride. Both
can be had in powder form - micron size or less. BN is very soft like
talc or graphite (sometimes sold as white graphite for its lubricating
properties) so particles could not produce much of a gap. AlN is harder
but milled fine enough it might be slightly better than BN.

http://www.bn.saint-gobain.com/
http://www.bn.saint-gobain.com/bn-electronics.aspx
https://en.wikipedia.org/wiki/Boron_nitride

The silver and copper filled stuff makes me nervous if it's in grease
form - I wouldn't want that crap dribbling into the electronics.

--
Grizzly H.

[tabb...@gmail.com]

On Saturday, 12 December 2015 21:44:50 UTC, mixed nuts wrote:

> I think that's correct - the grease would have to be very heavily loaded
> and under extremely high clamping force to embed the particles and make
> a dramatic difference.
>
> Most of the greases and thermal (not electrically conductive) adhesives
> are filled with hexagonal Boron Nitride and/or Aluminum Nitride. Both
> can be had in powder form - micron size or less. BN is very soft like
> talc or graphite (sometimes sold as white graphite for its lubricating
> properties) so particles could not produce much of a gap. AlN is harder
> but milled fine enough it might be slightly better than BN.
>
> http://www.bn.saint-gobain.com/
> http://www.bn.saint-gobain.com/bn-electronics.aspx
> https://en.wikipedia.org/wiki/Boron_nitride
>
> The silver and copper filled stuff makes me nervous if it's in grease
> form - I wouldn't want that crap dribbling into the electronics.

I tried toothpaste a while back on a 125W AMD CPU, as I couldn't find my stuff and wanted to get it done. It ran all of 1C hotter than with zinc oxide paste. That's silica IIRC.


NT

[Jeff Liebermann]

On Sat, 12 Dec 2015 11:54:46 -0800 (PST), whit3rd <whi...@gmail.com>

wrote:

>On Saturday, December 12, 2015 at 10:13:06 AM UTC-8, Jeff Liebermann wrote:
>> On Fri, 11 Dec 2015 19:45:09 -0800 (PST), whit3rd <whi...@gmail.com>
>> wrote:
>
>[about growing rubies]
>> >Or just buy 'em. Ten-millimeter round faceted will set you back
>> >maybe 2 bucks each, after shipping
>> ><http://www.gemsngems.com>
>>
>> Find a cheaper source. For 10 mm round they want $135/ea:
>> <http://www.gemsngems.com/product-category/lab-created-gemstones/hydrothermal-ruby/round-hydrothermal-ruby/>

>There's multiple processes and recipes; I was looking at a less expensive variant:
><http://www.gemsngems.com/product-category/lab-created-corundum/lab-created-ruby-5/round-lab-created-ruby-5/>

That's the same supplier and page that I linked, except I'm on Page 2,
where the 10 mm prices are listed. $135/ea.

I couldn't find anything on making rubies in a microwave oven, but did
find this on making zircons:
<http://www.yourgemologist.com/CubicZirconia/cubiczirconia.html>
and diamonds:
<http://wonderfulengineering.com/people-are-making-diamonds-in-microwave-ovens-heres-how-you-can-make-one-too/>
in a microwave oven. Do you perhaps have a better reference for
rubies?

[Jeff Liebermann]

On Sat, 12 Dec 2015 15:51:15 -0500, Phil Hobbs
<pcdhSpamM...@electrooptical.net> wrote:

>The problem with grease is that it tends to pump itself out from under
>the hot spots under temperature cycling. If one could get the diamond
>particles to embed themselves in both sides of the metal, they'd stay
>put and probably improve the theta.

In a past life, I was responsible for getting the heat out of RF power
transistors. I posted my results, which didn't quite agree with the
internet published orthodoxy, about 2 years ago in this newsgroup.
Now, I can't find it. Argh.

Very roughly, I got best results when I polished both the aluminum
heat sink and the base of the power xsistor. The idea was to get as
much metal to metal contact as possible. What worked best was no
grease, no powders, and no mixes of grease and powders. Just metal to
metal. However, that requires that both the heat sink and xsistor be
flat and parallel, not twisted, bent, or torqued. Measuring the
flatness of the heat sink was fairly easy. I can't say the same for
the xsistor. So, I just tested for stiction against a known flat
gauge block. Good enough.

During the testing, I tried various powdered metals without any greasy
binder. I didn't have a wide selection of powders available, but I
managed to try silicon carbide, graphite, metallic silver, alumina,
and copper. I would say that powdered silver worked about the same as
Arctic Silver heat sink goo. The best of the bunch was silver.
W/m*K
Diamond 1000
h-BN 600
c-BN 740
Silver 406
Copper 385
Gold 314
Aluminum 205
Graphite 200
Carbon 150
SiC 120
Brass 109

The idea behind the powder was to force the powdered metal particles
into the aluminum heat sink and copper xsistor base, filling in the
cracks and crevasses in the metal. In order to make that work, I had
to clean/degrease the parts, smear on the powder, wipe off the excess,
attach the transistor, and compress the mounting flange. If I had
left a large quantity of powder on the heat sink, it would make things
much worse. Inspecting the surface with a microscope showed that most
(not all) of the particles were imbedded in the aluminum.

However, the copper xsistor base was another story. Most of the
particles would just stick to the surface and not fill the cracks. I
could beat on the xsistor to force the particles into the xsistor
base, but that would cause the base to loose its flat surface. I
could have left the gold plating on the base, but then it wouldn't be
flat.

One thing I didn't try was gold leaf. Working with power transistor
size pieces of gold leaf is difficult. It sticks to literally
anything and will not let go. It also likes to wrinkle creating
lumps. However, with a fairly high thermal conductivity and the
ability to fill in cracks, it's still tempted to fight the problems.

The bottom line is that powder only made sense if both metals were
soft, polished, flat and parallel. Controlling the amount of powder
was difficult because the amount needed depended on the type and depth
of the surface features, cracks and roughness.

In the end, we used a polished heat sink and xistor for the really
high power stuff, and conventional heat sink goo for most everything
else. It was possible to get an improvement by using some of the
aforementioned methods, but it just wasn't worth the time and effort.

[tabb...@gmail.com]

What, you didn't try toothpaste? :)


NT

[Jeff Liebermann]

On Sat, 12 Dec 2015 16:39:32 -0800 (PST), tabb...@gmail.com wrote:

>What, you didn't try toothpaste? :)

If I repeated the tests today, I wouldn't bother with toothpaste.
Toothpaste is 20-42% water, which has a lousy thermal conductivity
(0.6 W/m-K). If I evaporated the water AFTER installing, there will
be air gaps. No thanks.

Instead, I would try gold leaf (314 W/m-k) again and add flake
graphite (750 W/m-K):
"THERMAL CONDUCTIVITY OF GRAPHITE FLAKE COMPOSITES"
<http://acs.omnibooksonline.com/data/papers/2007_C081.pdf>

Also, note that the differences between the various compounds is in
the area of 0.1 C/Watt. That doesn't seem like much until you try to
dissipate 150 watts per device:
0.1 * 150 = 15 C
which can be the difference between running hot and meltdown.

[John Larkin]

On Sat, 12 Dec 2015 15:51:15 -0500, Phil Hobbs
<pcdhSpamM...@electrooptical.net> wrote:

Do you think so? That would only be a problem if air moved in, to
replace the grease in the gaps.

[tabb...@gmail.com]

On Sunday, 13 December 2015 03:21:13 UTC, Jeff Liebermann wrote:

> On Sat, 12 Dec 2015 16:39:32 -0800 (PST), nt wrote:
>
> >What, you didn't try toothpaste? :)
>
> If I repeated the tests today, I wouldn't bother with toothpaste.
> Toothpaste is 20-42% water, which has a lousy thermal conductivity
> (0.6 W/m-K). If I evaporated the water AFTER installing, there will
> be air gaps. No thanks.

hence the smiley

> Instead, I would try gold leaf (314 W/m-k) again and add flake
> graphite (750 W/m-K):
> "THERMAL CONDUCTIVITY OF GRAPHITE FLAKE COMPOSITES"
> <http://acs.omnibooksonline.com/data/papers/2007_C081.pdf>

how would gold leaf help? To get it to squash into the crevices and out of the both-flat areas you'd need to put huge force on it. If you don't, it's just another impedance in the way. Unfortunately the same is true of any solid - and also I suspect why grease didn't work well for you. As the gap narrows, grease at some point becomes too stiff to flow through such tiny gaps, so you end up with grease separating the 2 surfaces.

> Also, note that the differences between the various compounds is in
> the area of 0.1 C/Watt. That doesn't seem like much until you try to
> dissipate 150 watts per device:
> 0.1 * 150 = 15 C
> which can be the difference between running hot and meltdown.

NT

[Jeff Liebermann]

On Sat, 12 Dec 2015 19:45:44 -0800 (PST), tabb...@gmail.com wrote:

>hence the smiley

I don't do smileys. Hieroglyphics went away with the ancient
Egyptians.

>> Instead, I would try gold leaf (314 W/m-k) again and add flake
>> graphite (750 W/m-K):
>> "THERMAL CONDUCTIVITY OF GRAPHITE FLAKE COMPOSITES"
>> <http://acs.omnibooksonline.com/data/papers/2007_C081.pdf>

>how would gold leaf help? To get it to squash into the crevices
>and out of the both-flat areas you'd need to put huge force on
>it. If you don't, it's just another impedance in the way.

Thermal resistance, not impedance. There's no imaginary part.

Gold leaf has better thermal conductivity than most of the pastes and
powders. Visualize to non-mating surfaces full of cracks, but
reasonably flat. The surfaces will touch only at the highest peaks,
leaving air pockets in the gaps and cracks. The gold leaf is thin
enough that the touching peaks will push aside some of the old and
either down the sides of the peaks, or into the cracks. It won't fill
the cracks as a grease or powder might, but will have three high
thermally conductive materials touching. Unfortunately, I don't have
a sectioning saw necessary to produce a microscope cross section photo
to see what the gold is really doing.

>Unfortunately the same is true of any solid - and also I suspect
>why grease didn't work well for you. As the gap narrows, grease
>at some point becomes too stiff to flow through such tiny gaps,
>so you end up with grease separating the 2 surfaces.

Nope. The problem with grease is determining how much to use. If the
grease is thick, and I use too much, the cracks are filled, but
there's also a rather thick layer of comparatively high thermal
resistance grease sitting between the heat sink and the xsistor. If I
use very thin grease (i.e. oil), then it just leaks out of the joint
and loosens the torque on the mounting screws. A compromise is
needed.

The best way to do grease, paste, and powder is to thinly smear the
paste onto both the aluminum and copper down to where you can see both
grease and metal sticking through the grease. In other words, fill
the cracks, but don't go over the metal peaks. Then assemble and
compress. That uses an amazingly small amount of thermal grease.
However, there are a few problems. It doesn't work well if either
part is twisted. If not done right, it will also leave the sides of
the metal peaks uncovered. I originally used the end of an acrylic
ruler to apply the grease. That worked well until the end of the
ruler showed grooves resulting in grease ridges on the heat sink. I'm
not sure what to use now, but I suspect it will need to be harder than
aluminum.

Anyway, my problems with grease were probably from applying the grease
either too thick or too thin.

<http://www.ebay.com/itm/272017489895>

[John Larkin]

On Sat, 12 Dec 2015 20:46:22 -0800, Jeff Liebermann <je...@cruzio.com>
wrote:

Dow 340 squishes out from under a part with modest pressure. It flows.
I don't think that too thick is a problem.

I measured 100 microinches thickness added by some, which was my limit
of measurement resolution with a micrometer. It may squish thinner.

Bubbles/air gaps could be a problem. I think that the best application
is one drop in the middle of a part, then press onto the sink with a
circular motion, until grease exudes all around the edges of the part.

[tabb...@gmail.com]

On Sunday, 13 December 2015 04:46:27 UTC, Jeff Liebermann wrote:

> On Sat, 12 Dec 2015 19:45:44 -0800 (PST), nt wrote:

> >> Instead, I would try gold leaf (314 W/m-k) again and add flake
> >> graphite (750 W/m-K):
> >> "THERMAL CONDUCTIVITY OF GRAPHITE FLAKE COMPOSITES"
> >> <http://acs.omnibooksonline.com/data/papers/2007_C081.pdf>
>
> >how would gold leaf help? To get it to squash into the crevices
> >and out of the both-flat areas you'd need to put huge force on
> >it. If you don't, it's just another impedance in the way.
>
> Thermal resistance, not impedance. There's no imaginary part.
>
> Gold leaf has better thermal conductivity than most of the pastes and
> powders. Visualize to non-mating surfaces full of cracks, but
> reasonably flat. The surfaces will touch only at the highest peaks,
> leaving air pockets in the gaps and cracks. The gold leaf is thin
> enough that the touching peaks will push aside some of the old and
> either down the sides of the peaks, or into the cracks.

You reckon that with only hand pressure, the solid metal gold will flow sideways from under the peaks. I have to say that sounds optimistic - you've clearly done a lot more work on this than I have, but that is a bold claim, and I think would warrant some sort of measurement of whether that does happen.

> It won't fill
> the cracks as a grease or powder might,

no, and there's its other problem. There's so little bulk that I wouldn't expect it to do much in the crevices.

> but will have three high
> thermally conductive materials touching. Unfortunately, I don't have
> a sectioning saw necessary to produce a microscope cross section photo
> to see what the gold is really doing.

I wonder if there's any other way to do it

> >Unfortunately the same is true of any solid - and also I suspect
> >why grease didn't work well for you. As the gap narrows, grease
> >at some point becomes too stiff to flow through such tiny gaps,
> >so you end up with grease separating the 2 surfaces.
>
> Nope. The problem with grease is determining how much to use. If the
> grease is thick, and I use too much, the cracks are filled, but
> there's also a rather thick layer of comparatively high thermal
> resistance grease sitting between the heat sink and the xsistor. If I
> use very thin grease (i.e. oil), then it just leaks out of the joint
> and loosens the torque on the mounting screws. A compromise is
> needed.
>
> The best way to do grease, paste, and powder is to thinly smear the
> paste onto both the aluminum and copper down to where you can see both
> grease and metal sticking through the grease. In other words, fill
> the cracks, but don't go over the metal peaks. Then assemble and
> compress. That uses an amazingly small amount of thermal grease.
> However, there are a few problems. It doesn't work well if either
> part is twisted. If not done right, it will also leave the sides of
> the metal peaks uncovered.

FWIW my observations of used parts in commercial domestic equipment is that there's always a nearly whole layer of grease left between the 2 surfaces. Maybe that's just because they're so far from flat, I don't know.

> I originally used the end of an acrylic
> ruler to apply the grease. That worked well until the end of the
> ruler showed grooves resulting in grease ridges on the heat sink. I'm
> not sure what to use now, but I suspect it will need to be harder than
> aluminum.

Would a single scrape with a regular steel scraper produce significant surface damage? If so I guess you just have to keep regrinding something soft.

> Anyway, my problems with grease were probably from applying the grease
> either too thick or too thin.
>
> <http://www.ebay.com/itm/272017489895>

I came across the flow problem when trying to pass regular engine oil through a 1mm nozzle. Getting it to move at all proved beyond the physical limits of the equipment.


NT

[Phil Hobbs]

On 12/12/2015 10:21 PM, Jeff Liebermann wrote:
> On Sat, 12 Dec 2015 16:39:32 -0800 (PST), tabb...@gmail.com wrote:
>
>> What, you didn't try toothpaste? :)
>
> If I repeated the tests today, I wouldn't bother with toothpaste.
> Toothpaste is 20-42% water, which has a lousy thermal conductivity
> (0.6 W/m-K). If I evaporated the water AFTER installing, there will
> be air gaps. No thanks.
>
> Instead, I would try gold leaf (314 W/m-k) again and add flake
> graphite (750 W/m-K):
> "THERMAL CONDUCTIVITY OF GRAPHITE FLAKE COMPOSITES"
> <http://acs.omnibooksonline.com/data/papers/2007_C081.pdf>
>
> Also, note that the differences between the various compounds is in
> the area of 0.1 C/Watt. That doesn't seem like much until you try to
> dissipate 150 watts per device:
> 0.1 * 150 = 15 C
> which can be the difference between running hot and meltdown.
>

Some friends of mine developed a couple of interesting technologies for
metallic thermal interface materials (TIMs). One is an indium-gallium
liquid alloy that was used in some higher end Apple machines. It works
the best of anything, but is vulnerable to corrosion. The other is
indium foil with a very small quilt pattern embossed in it. Both work
dramatically better than the best paste. The quilt pattern allows the
metal to conform better to the surfaces, because it only has to flow a
short distance to get out from under a high spot. Either one is good
enough for a 2500-sun solar concentrator--in fact it was the metal TIM
that made the concentrator possible. (I did a little work on the solar
project, but not on the TIMs, except to cheer from the sidelines.)

The best paste as of 2007ish came in at about 3.5 W/m/K. It was made by
a Japanese outfit whose name I forget--it had tiny flat metal flakes in
it, which were supposed to form stacks so that most of the heat went
through a solid metal path. It turned out that the stacks performed
worst under temperature cycling. Since the stacks were pinned in place,
expansion of the grease washed the small particles out from between the
flakes, which dramatically increased the thermal resistance.

Cheers

Phil Hobbs

[Neon John]

On Sat, 12 Dec 2015 11:40:04 -0800, John Larkin

>Given a typical power mosfet (very flat) and a typical extruded heat
>sink (not very flat) Dow 340 will cut theta by a factor of 3 or so.
>I'm guessing (pat pending) that diamond-grit goop wouldn't be
>dramatically better.
>

John, I'm using Laird T52-1 Tguard phase change pad for the power
transistors in my induction heaters. This is a micro-thin sheet of
kapton with a filled wax coating on each side that melts at about 40
deg C. The wax melts and fills the irregularities. My heat sinks are
either machined or extruded.

Laird claims and I've measured 0.13 deg C/Watt per side with this
stuff using an actual transistor as the heat source.

Do you think the Dow 304 with the same thickness kapton could beat
that? I'd love to find something a bit more thermally conductive,
though the 0.32 deg/W for the die to substrate isn't helping things
all that much.

John
John DeArmond
http://www.neon-john.com
http://www.fluxeon.com
Tellico Plains, Occupied TN
See website for email address

[DecadentLinuxUserNumeroUno]

On Sun, 13 Dec 2015 11:27:47 -0500, Neon John <n...@never.com> Gave us:

Use hard anodized Al for the sink. That surface is non conductive (if
done to mil spec)..
Then use silver filled epoxy for the attach. That is what chip makers
use to attach the die to the substrate.

Better might be to use a paper thin anodized Al sheet clad onto a
copper mass for the sink.

[Joseph Gwinn]

On Dec 12, 2015, Jeff Liebermann wrote
(in article<ufsp6b1e0dhcao1ui...@4ax.com>):

> On Sat, 12 Dec 2015 19:45:44 -0800 (PST), tabb...@gmail.com wrote:
>
> > hence the smiley
>
> I don't do smileys. Hieroglyphics went away with the ancient
> Egyptians.
>
> > > Instead, I would try gold leaf (314 W/m-k) again and add flake
> > > graphite (750 W/m-K):
> > > "THERMAL CONDUCTIVITY OF GRAPHITE FLAKE COMPOSITES"
> > > <http://acs.omnibooksonline.com/data/papers/2007_C081.pdf>
>
> > how would gold leaf help? To get it to squash into the crevices
> > and out of the both-flat areas you'd need to put huge force on
> > it. If you don't, it's just another impedance in the way.
>
> Thermal resistance, not impedance. There's no imaginary part.
>
> Gold leaf has better thermal conductivity than most of the pastes and
> powders. Visualize to non-mating surfaces full of cracks, but
> reasonably flat. The surfaces will touch only at the highest peaks,
> leaving air pockets in the gaps and cracks. The gold leaf is thin
> enough that the touching peaks will push aside some of the old and
> either down the sides of the peaks, or into the cracks. It won't fill
> the cracks as a grease or powder might, but will have three high
> thermally conductive materials touching. Unfortunately, I don't have
> a sectioning saw necessary to produce a microscope cross section photo
> to see what the gold is really doing.

An ordinary vertical mill with a saw blade will do. The key is to embed the
specimen in epoxy, cut, and polish the cut face using wet/dry sandpaper
followed by metallurgical polishing film (diamond dust in mylar film) face up
on a sheet of float glass.

Joe Gwinn

[John Larkin]

On Sun, 13 Dec 2015 11:27:47 -0500, Neon John <n...@never.com> wrote:

>On Sat, 12 Dec 2015 11:40:04 -0800, John Larkin
>>Given a typical power mosfet (very flat) and a typical extruded heat
>>sink (not very flat) Dow 340 will cut theta by a factor of 3 or so.
>>I'm guessing (pat pending) that diamond-grit goop wouldn't be
>>dramatically better.
>>
>
>John, I'm using Laird T52-1 Tguard phase change pad for the power
>transistors in my induction heaters. This is a micro-thin sheet of
>kapton with a filled wax coating on each side that melts at about 40
>deg C. The wax melts and fills the irregularities. My heat sinks are
>either machined or extruded.
>
>Laird claims and I've measured 0.13 deg C/Watt per side with this
>stuff using an actual transistor as the heat source.
>
>Do you think the Dow 304 with the same thickness kapton could beat
>that? I'd love to find something a bit more thermally conductive,
>though the 0.32 deg/W for the die to substrate isn't helping things
>all that much.

Kapton has a high thermal resistance, maybe OK if it's really thin.

The phase-change stuff that I've tried was terrible, because it was
thick and didn't really flow out from under the part. There's probably
better stuff around. If it really liquifies and flows, it's probably
OK.

If you need low theta and insulation, you might consider a thin slab
of lapped AlN and grease or epoxy. I'm seeing prices like $1.50 for a
TO247-size piece, 10 or 15 mils thick. Of if the voltage is low,
under 100 volts maybe, grease over 1 mil thick hard anodize, as the
Decadent guy suggests.

If thing get hardcore, use a copper heat spreader and grease, and bolt
the copper to an anodized aluminum heat sink. That will do good
lateral heat spreading, which can be the bottleneck with aluminum. The
spreader magnifies the area of the insulator, too.

I want blocks of solid isotopically-pure diamond. I wonder why diamond
is so hard to make.

[whit3rd]

On Saturday, December 12, 2015 at 3:42:03 PM UTC-8, Jeff Liebermann wrote:
> On Sat, 12 Dec 2015 11:54:46 -0800 (PST), whit3rd <whi...@gmail.com>
> wrote:

> >[about growing rubies]
> >> >Or just buy 'em. Ten-millimeter round faceted will set you back
> >> >maybe 2 bucks each, after shipping
> >> ><http://www.gemsngems.com>

> >> Find a cheaper source. For 10 mm round they want $135/ea:
> >> <http://www.gemsngems.com/product-category/lab-created-gemstones/hydrothermal-ruby/round-hydrothermal-ruby/>
>
> >There's multiple processes and recipes; I was looking at a less expensive variant:
> ><http://www.gemsngems.com/product-category/lab-created-corundum/lab-created-ruby-5/round-lab-created-ruby-5/>
>
> That's the same supplier and page that I linked, except I'm on Page 2,
> where the 10 mm prices are listed. $135/ea.

Double-check that; your browser may be doing autocomplete behind your back.
Those are the same supplier, but very different pages.
Hydrothermal is a pressure-cooker crystal growth scheme, while the less expensive
comes from a Czochralski type plasma scheme, which has more impurities and flaws (this
might be OK, if you wanted a star ruby).
I'm not sure how either scheme would work out in a garage or kitchen.

[Jeff Liebermann]

On Sun, 13 Dec 2015 12:26:11 -0800 (PST), whit3rd <whi...@gmail.com>

wrote:

>On Saturday, December 12, 2015 at 3:42:03 PM UTC-8, Jeff Liebermann wrote:
>> On Sat, 12 Dec 2015 11:54:46 -0800 (PST), whit3rd <whi...@gmail.com>
>> wrote:
>
>> >[about growing rubies]
>> >> >Or just buy 'em. Ten-millimeter round faceted will set you back
>> >> >maybe 2 bucks each, after shipping
>> >> ><http://www.gemsngems.com>
>
>> >> Find a cheaper source. For 10 mm round they want $135/ea:
>> >> <http://www.gemsngems.com/product-category/lab-created-gemstones/hydrothermal-ruby/round-hydrothermal-ruby/>
>>
>> >There's multiple processes and recipes; I was looking at a less expensive variant:
>> ><http://www.gemsngems.com/product-category/lab-created-corundum/lab-created-ruby-5/round-lab-created-ruby-5/>
>>
>> That's the same supplier and page that I linked, except I'm on Page 2,
>> where the 10 mm prices are listed. $135/ea.

>Double-check that; your browser may be doing autocomplete behind your back.
>Those are the same supplier, but very different pages.

Bingo. After flushing my cache and checking the URL, I get a cheaper
page. However, 10 mm is now $25 and far away from $2/ea.
<http://www.gemsngems.com/product-category/lab-created-corundum/lab-created-ruby-5/round-lab-created-ruby-5/page/2/>

>Hydrothermal is a pressure-cooker crystal growth scheme, while the less expensive
>comes from a Czochralski type plasma scheme, which has more impurities and flaws (this
>might be OK, if you wanted a star ruby).
>I'm not sure how either scheme would work out in a garage or kitchen.

Thanks, but growing crystals and semiconductor processes are some of
the many areas of electronics about which I know nothing. I found a
bit more on growing various crystals in a microwave oven, but nothing
for rubies.

[Jeff Liebermann]

On Sun, 13 Dec 2015 19:11:39 -0800, Jeff Liebermann <je...@cruzio.com>
wrote:

>Bingo. After flushing my cache and checking the URL, I get a cheaper
>page. However, 10 mm is now $25 and far away from $2/ea.
><http://www.gemsngems.com/product-category/lab-created-corundum/lab-created-ruby-5/round-lab-created-ruby-5/page/2/>

Oops. Different mistake this time. The $25 is the "lot" price for
$25 pieces. The unit price is $1.28, which is less than $2.00.
Sorry(tm).

[DecadentLinuxUserNumeroUno]

On Sun, 13 Dec 2015 09:58:25 -0800, John Larkin
<jjla...@highlandtechnology.com> Gave us:

>I want blocks of solid isotopically-pure diamond. I wonder why diamond
>is so hard to make.

Maybe they'll make some fine grain diamond in a graphene sheet matrix.

I think that sounds pretty good, actually.

Not thermally related, but DARPA got the world record for highest
frequency amplifier. They use HEMT and they are using a vacuum to get
Terahertz operation.

https://www.google.com/?gws_rd=ssl#q=DARPA+gets+world+record

[Bill Beaty]

On Saturday, December 12, 2015 at 7:21:13 PM UTC-8, Jeff Liebermann wrote:

> On Sat, 12 Dec 2015 16:39:32 -0800 (PST), tabbypurr wrote:
>
> >What, you didn't try toothpaste? :)
>
> If I repeated the tests today,

Or low-temp solder? Even room-temp solder?

Possibly destroys Al heatsinks progressively when warm, same as mercury does.

Do copper slabs display mercury rot, LME, like aluminum has?

[amdx]

We used a silver filled sheet epoxy for bonding PZT8 piezo ceramics to
aluminum. But first the two surfaces were abraded against each other
with a carborundum abrasive using a figure 8 pattern and constantly
rotating the ceramic. The aluminum, sheet epoxy and ceramic were mounted
on a heated clamping assembly with 20 psi of clamp pressure.
These were 2"round ceramics on a 4" round aluminum piece.
Mikek

[Phil Hobbs]

Lapping in the surfaces can help a lot. One tip (that I learned from
Usenet) is that lapping two surfaces makes them both spherical (with
some very large radius in this case), but using three surfaces and
lapping them pairwise forces all the radii to infinity, i.e. all three
surfaces become very flat.

The reason for this, I think, is that the constant change of direction
and orientation forces the surfaces to be spheres (i.e. independent of
orientation), and the odd number of surfaces means that the surface
can't be either concave or convex. If two of the surfaces were convex
and one concave the two convex ones would flatten each other out in the
middle when they were lapped together, which would force the third
surface to become flatter as well. That means that the three surfaces
all tend to become spheres of infinite radius, i.e. planes.

[amdx]

Mental block, lapping was the term I wanted :-)
Any radii created by lapping was much less of a problem than the
difference in expansion of the ceramic vs aluminum. After the transducer
had cooled it had a slight concaved surface. It wasn't a problem in use,
just an observation. It also produced a big spark
when it cooled.
Mikek

[Phil Hobbs]

Yes, one problem with a too-thin bond line is that the shear stress in
the cement is maximized. Something a bit thicker can accommodate the
thermal expansion a bit.

[amdx]

We didn't have delaminating issues, our big thing was efficiency of
the finished transducer. A thicker bond line, generally caused lower
efficiency. We were driving a 2" diameter ceramic with 250 Watts
continuous and 1000 Watts pulsed.
I miss that job, we had lots of fun!
Mikek

[DecadentLinuxUserNumeroUno]

On Mon, 14 Dec 2015 07:42:51 -0500, Phil Hobbs
<pcdhSpamM...@electrooptical.net> Gave us:

The reason for abrading the surfaces is so that the epoxy will have
better adhesion. The reason to do one with the other is for a
mating/coplanarity improvement.

The main reason, however is because if left smooth, the epoxy can
detach very easily. The abrading makes tiny hooks for it to grab onto,
which increases the pressure required to create a detachment event.

[Phil Hobbs]

>have better adhesion.  The reason to do one with the other is for a
>mating/coplanarity improvement.

>  The main reason, however is because if left smooth, the epoxy can
>detach very easily.  The abrading makes tiny hooks for it to grab onto,
>which increases the pressure required to create a detachment event.

Lapping solves all those problems at once. Fine valve grinding compound is one approach--it gets the surfaces close but leaves a bit of 'tooth'.

For mounting TECs, it's best to use diamond grit because emery is Al2O3 like the TEC end plates, and so doesn't polish them very well (it does work eventually).

Cheers

Phil Hobbs

[Jeff Liebermann]

On Sun, 13 Dec 2015 23:02:49 -0800 (PST), Bill Beaty
<bi...@eskimo.com> wrote:

>On Saturday, December 12, 2015 at 7:21:13 PM UTC-8, Jeff Liebermann wrote:
>> On Sat, 12 Dec 2015 16:39:32 -0800 (PST), tabbypurr wrote:
>>
>> >What, you didn't try toothpaste? :)
>>
>> If I repeated the tests today,

>Or low-temp solder? Even room-temp solder?

Not me. With RF power transistors, I have one advantage over
transducers and such. RF transistor flange mounts are bolted to the
heat sink. There's no need for the heat sink compound to have any
adhesive properties. Therefore, I don't need to solder, bond, or glue
anything together. So low-temp solder won't be on my short list.
However, that doesn't stop people from trying it. Here's an example:
<http://www.w6pql.com/70cm/500wassembly.htm>
Looks like only the ends of the flange mount are soldered.

Solder also isn't that wonderful a thermal conductor, even with silver
added:
<http://www.electronics-cooling.com/2006/08/thermal-conductivity-of-solders/>
I'm looking for thermal paste with the highest possible conductivity,
that doesn't ruin the budget and is manufacturable by mere mortals.
For example, I won't be looking into brazing or soldering the copper
transistor base to the aluminum heat sink because the process will
probably destroy the transistor junctions and warp the heat sink. It
also makes replacing RF power transistors rather difficult.

>Possibly destroys Al heatsinks progressively when warm, same as mercury does.
>Do copper slabs display mercury rot, LME, like aluminum has?

Dunno.

[Jeff Liebermann]

On Sun, 13 Dec 2015 11:16:05 -0500, Phil Hobbs
<pcdhSpamM...@electrooptical.net> wrote:

>Some friends of mine developed a couple of interesting technologies for
>metallic thermal interface materials (TIMs). One is an indium-gallium
>liquid alloy that was used in some higher end Apple machines. It works
>the best of anything, but is vulnerable to corrosion.

PowerMac G5 quad core, methinks. I think it acted like solder paste,
not the usual heat sink goo, but I'm not sure. Apple also did a
Delphi liquid cooling in the quad core G5 machine which uses some kind
of exotic thermal paste. Indium-gallium sounds expensive.

These look like solders, or maybe solder paste:
<http://www.indium.com/thermal-management/thermal-k-list/>

>The other is
>indium foil with a very small quilt pattern embossed in it.

W/m*K
Indium (pure) 86
Gold leaf 314

>Both work
>dramatically better than the best paste.

I would think that gold leaf would work better. However, gold leaf is
a nightmare to handle (and subject to assembly line shrinkage). Look
like it's more expensive than gold:
<http://www.ebay.com/sch/i.html?_nkw=indium+foil>
0.05 and 0.1 mm thickness should work, especially if it's easier to
handle than gold foil.

>The quilt pattern allows the
>metal to conform better to the surfaces, because it only has to flow a
>short distance to get out from under a high spot.

Good idea. I've never played with indium foil. Is it malleable?

>Either one is good
>enough for a 2500-sun solar concentrator--in fact it was the metal TIM
>that made the concentrator possible. (I did a little work on the solar
>project, but not on the TIMs, except to cheer from the sidelines.)

For RF, the best I've done is 300 watts CW through about 120 sq-mm
flange mount or:
300 / 120 = 2.5 watts/sq-mm
I think I can do better with todays GaN power devices.

One sun is 1000 watts/sq-meter = 0.001 watts/sq-mm.
2500 suns * 0.001 watts/sq-mm = 2.5 watts/sq-mm.
Hmmm... that number looks familiar.

>The best paste as of 2007ish came in at about 3.5 W/m/K. It was made by
>a Japanese outfit whose name I forget--it had tiny flat metal flakes in
>it, which were supposed to form stacks so that most of the heat went
>through a solid metal path. It turned out that the stacks performed
>worst under temperature cycling. Since the stacks were pinned in place,
>expansion of the grease washed the small particles out from between the
>flakes, which dramatically increased the thermal resistance.

That's the same idea behind the carbon flake thermal "paste".

I forgot to mumble something about press fitting the transitor copper
flanges into the aluminum. The idea was to eliminate the thermal
grease and get a metal-to-metal air tight fit. It would also add the
sides of the transistor flange to the surface area. It didn't work
because I never could totally eliminate all the air gaps and the
xsistor manufacturers (TRW, CTC, etc) never could maintain their case
tolerances. Oh well.

[John Larkin]

On Mon, 14 Dec 2015 08:11:15 -0800, Jeff Liebermann <je...@cruzio.com>
wrote:

It often makes sense to use more semiconductors and spread the heat
out. That's easy at low frequencies, harder at RF.

Transistors often cost less than heat sinks!

[Phil Hobbs]

The problem with gold foil is that if you clamp it between two pieces of
metal, it disappears--it wants very badly to form an amalgam at the surface.

>
>> The quilt pattern allows the
>> metal to conform better to the surfaces, because it only has to flow a
>> short distance to get out from under a high spot.
>
> Good idea. I've never played with indium foil. Is it malleable?

Very. Softer than Sn63 solder by a lot. It's often used as the O-ring
in cryostats.

>
>> Either one is good
>> enough for a 2500-sun solar concentrator--in fact it was the metal TIM
>> that made the concentrator possible. (I did a little work on the solar
>> project, but not on the TIMs, except to cheer from the sidelines.)
>
> For RF, the best I've done is 300 watts CW through about 120 sq-mm
> flange mount or:
> 300 / 120 = 2.5 watts/sq-mm
> I think I can do better with todays GaN power devices.
>
> One sun is 1000 watts/sq-meter = 0.001 watts/sq-mm.
> 2500 suns * 0.001 watts/sq-mm = 2.5 watts/sq-mm.
> Hmmm... that number looks familiar.

Yep, but solar cells have to run cooler, because you lose power output
really badly otherwise--the series resistance goes up and the open
circuit voltage drops.

>
>> The best paste as of 2007ish came in at about 3.5 W/m/K. It was made by
>> a Japanese outfit whose name I forget--it had tiny flat metal flakes in
>> it, which were supposed to form stacks so that most of the heat went
>> through a solid metal path. It turned out that the stacks performed
>> worst under temperature cycling. Since the stacks were pinned in place,
>> expansion of the grease washed the small particles out from between the
>> flakes, which dramatically increased the thermal resistance.
>
> That's the same idea behind the carbon flake thermal "paste".
>
> I forgot to mumble something about press fitting the transitor copper
> flanges into the aluminum. The idea was to eliminate the thermal
> grease and get a metal-to-metal air tight fit. It would also add the
> sides of the transistor flange to the surface area. It didn't work
> because I never could totally eliminate all the air gaps and the
> xsistor manufacturers (TRW, CTC, etc) never could maintain their case
> tolerances. Oh well.
>

[Jeff Liebermann]

On Sat, 12 Dec 2015 21:31:12 -0800, John Larkin
<jjla...@highlandtechnology.com> wrote:

>Dow 340 squishes out from under a part with modest pressure. It flows.
>I don't think that too thick is a problem.

I think too thick is a problem when I'm trying to squeeze every last
possible watt out of the devices. The problem with Dow 340 is that it
continues to flow for weeks after installation. Try two small pieces
of steel with some Dow 340 in between. Use some 4-40 set screws to
compress the sandwich (same as in most RF power device mounting).
Torque to whatever your device specifies, but don't use spring
(Belville) washers or lockwashers to maintain tension. After a day or
so, re-torque the screws. You'll probably find that they've become
loose and require some tightening. This continues until you get to
metal on metal, which is where the sandwich should have been in the
first place before too much silicon grease was added.

You can do the same experiment with large metal packages (i.e. TO-3)
but the problem is different. Instead of the silicon grease oozing
out from under the device, the mounting flanges compress, the device
bends, and the silicon grease collects in the middle. However,
thermal cycling will eventually pump this accumulation out from under
the device, resulting in an air gap.

>I measured 100 microinches thickness added by some, which was my limit
>of measurement resolution with a micrometer. It may squish thinner.

I measured the capacitance between the device and an anodized
(insulated) heat sink. I have the numbers here somewhere but as I
recall, they were close to zero because the ideal amount of thermal
goo was where metal hit metal. I think my accuracy was limited by the
accuracy of my torque wrench, but I don't recall the relationship.

>Bubbles/air gaps could be a problem. I think that the best application
>is one drop in the middle of a part, then press onto the sink with a
>circular motion, until grease exudes all around the edges of the part.

Yep, that works and is what I try to do with CPU heat sinks. However,
most CPU sockets prevent that from working. So, I settle for smear
the goo on thick, wipe as much as possible off with a plastic blade,
attach. Using the CPU internal temp measurements and a CPU "exercise"
program, this works a few degrees better than anything else I've
tried.

[Jeff Liebermann]

On Mon, 14 Dec 2015 12:01:43 -0500, Phil Hobbs
<pcdhSpamM...@electrooptical.net> wrote:

>The problem with gold foil is that if you clamp it between two pieces of
>metal, it disappears--it wants very badly to form an amalgam at the surface.

As long as what's left fills in the cracks in the aluminum and copper,
it should work. I would be worried if the gold dissolved into the
aluminum or copper, but an amalgam (alloy) of gold and these two
materials, it should not shrink much. As I previously mumbled, I
haven't done much with the gold leaf and it's on my things to do list.
Besides, if there's any questions as to the expected results, I prefer
to see my own failures. Learn by Destroying(tm).

>Very. Softer than Sn63 solder by a lot. It's often used as the O-ring
>in cryostats.

Good. I'll add it to my short list. If it works, management can then
declare it too expensive, leaving me with what I originally wanted to
use as the winner. (red herring).

>Yep, but solar cells have to run cooler, because you lose power output
>really badly otherwise--the series resistance goes up and the open
>circuit voltage drops.

True, but ignoring the operating temperatures, comparing the thermal
resistances of the quilted indium foil with my tinkering is all I
wanted.

Please note that my testing of thermal pastes and assembly methods
were not exactly an organized project. I was trying to solve output
power variability problems in production as well as squeeze a few more
watts out of the available components to score a few points with
marketing. It was by no means an organized effort and was spread over
about 5 years of development on multiple products. Testing was
resumed many years later when I entered the computer repair biz, and
once again ran into the mysticism and magic that seems to surround
thermal management.

[Jeff Liebermann]

On Mon, 14 Dec 2015 08:58:04 -0800, John Larkin
<jjla...@highlandtechnology.com> wrote:

>It often makes sense to use more semiconductors and spread the heat
>out. That's easy at low frequencies, harder at RF.

My experience is from the marine radio business, where a few dollars
difference in selling price often made the difference in a sale. Well,
not so much at the retail level, but certainly when selling to fishing
fleets and distributors. So, we tried to use one RF power device in
as many places as possible. That means compromises and learning to
use mismatched and inferior components. At the time, there were only
a few RF power manufacturers, all with parts that were allegedly
compatible, but certainly not interchangeable. So, I had to design
boards for one specific manufacturer's power devices. Changing
vendors was not a trivial exercise. Today, due to automation and
larger quantities, such parts are more consistent, predictable, and
more available.

For RF, the limiting factor on obtaining rates power output is getting
the heat out of the device. Spreading the heat around over a larger
number of devices certainly would help. However, the cost and output
of RF power devices is not a linear relationship. Doubling the number
of 1/2 power RF devices would more than double the cost, as well as
introduce added losses in power combiner devices. The trend is in the
opposite direction, to put more dies into the power transistor
package. For example:
<http://www.northropgrumman.com/Capabilities/BipolarRFTransistors/PublishingImages/pageImages/BI-10002.jpg>

>Transistors often cost less than heat sinks!

Yep. Transistors get the benefit of automation. Heat sinks, much
less so. However, with todays higher efficiency switching amps (Class
D/E/F) and envelope tracking RF power amps, the total dissipation is
less, allowing a smaller and cheaper devices and heat sink. Progress
lurches forward.

[krw]

In the case of heat sinks, who cares if the surfaces are planes or
spheres? In fact, spherical sections would be *slightly* (read:
insignificantly) better.

[John Larkin]

On Mon, 14 Dec 2015 09:07:53 -0800, Jeff Liebermann <je...@cruzio.com>
wrote:

>On Sat, 12 Dec 2015 21:31:12 -0800, John Larkin
><jjla...@highlandtechnology.com> wrote:
>
>>Dow 340 squishes out from under a part with modest pressure. It flows.
>>I don't think that too thick is a problem.
>
>I think too thick is a problem when I'm trying to squeeze every last
>possible watt out of the devices. The problem with Dow 340 is that it
>continues to flow for weeks after installation.

That's a feature! But sometimes I think that a very thin, unfilled oil
is better if the surfaces are very flat.

Try two small pieces
>of steel with some Dow 340 in between. Use some 4-40 set screws to
>compress the sandwich (same as in most RF power device mounting).
>Torque to whatever your device specifies, but don't use spring
>(Belville) washers or lockwashers to maintain tension. After a day or
>so, re-torque the screws. You'll probably find that they've become
>loose and require some tightening. This continues until you get to
>metal on metal, which is where the sandwich should have been in the
>first place before too much silicon grease was added.

Some sorts of spring washers are necessary, especially if there's FR4
in the stack. FR4 cold-flows, so fasteners will loosen up. Wavy
washers are nice for PCBs, because they don't dig into the board and
make many contacts.

I got the 100 uinch measured gap with Dow 340, with just seconds of
pressure.

>
>You can do the same experiment with large metal packages (i.e. TO-3)
>but the problem is different. Instead of the silicon grease oozing
>out from under the device, the mounting flanges compress, the device
>bends, and the silicon grease collects in the middle. However,
>thermal cycling will eventually pump this accumulation out from under
>the device, resulting in an air gap.

Do you think so? Why would the air preferentially displace the
silicone?

>
>>I measured 100 microinches thickness added by some, which was my limit
>>of measurement resolution with a micrometer. It may squish thinner.
>
>I measured the capacitance between the device and an anodized
>(insulated) heat sink. I have the numbers here somewhere but as I
>recall, they were close to zero because the ideal amount of thermal
>goo was where metal hit metal. I think my accuracy was limited by the
>accuracy of my torque wrench, but I don't recall the relationship.
>
>>Bubbles/air gaps could be a problem. I think that the best application
>>is one drop in the middle of a part, then press onto the sink with a
>>circular motion, until grease exudes all around the edges of the part.
>
>Yep, that works and is what I try to do with CPU heat sinks. However,
>most CPU sockets prevent that from working. So, I settle for smear
>the goo on thick, wipe as much as possible off with a plastic blade,
>attach. Using the CPU internal temp measurements and a CPU "exercise"
>program, this works a few degrees better than anything else I've
>tried.

The smear-and-mount thing guarantees air gaps, in my opinion. I don't
know how to prove that.




--

John Larkin Highland Technology, Inc
picosecond timing precision measurement

jlarkin att highlandtechnology dott com
http://www.highlandtechnology.com

[John Larkin]

On Mon, 14 Dec 2015 09:50:12 -0800, Jeff Liebermann <je...@cruzio.com>
wrote:

At low frequencies, the tradeoff favors more cheap parts, like more
D2PAKs instead of 500 watt TO247 types. And pick-and-place is a lot
cheaper than hardware and screwdrivers.

[Phil Hobbs]

It would make the devices interchangeable, which would be nice from a
servicing point of view.

[Phil Hobbs]

It does--I've seen lots of pictures from my old colleagues in the
Packaging Research Department at IBM. (It was a weird place to be doing
MIM tunnel junctions, but the people were nice.)

Thermal expansion pushes the paste out, but once it's out, there's
nothing to pull it back in as the temperature drops again. So
eventually it pumps out. Putting paste reservoirs underneath helps,
because they're sealed from the atmosphere, so there actually is a
restoring force.

[Phil Hobbs]

On 12/14/2015 12:27 PM, Jeff Liebermann wrote:
> On Mon, 14 Dec 2015 12:01:43 -0500, Phil Hobbs
> <pcdhSpamM...@electrooptical.net> wrote:
>
>> The problem with gold foil is that if you clamp it between two pieces of
>> metal, it disappears--it wants very badly to form an amalgam at the surface.

>
> As long as what's left fills in the cracks in the aluminum and copper,
> it should work. I would be worried if the gold dissolved into the
> aluminum or copper, but an amalgam (alloy) of gold and these two
> materials, it should not shrink much. As I previously mumbled, I
> haven't done much with the gold leaf and it's on my things to do list.
> Besides, if there's any questions as to the expected results, I prefer
> to see my own failures. Learn by Destroying(tm).

If it amalgamates faster than it flows, all it'll do is harden the metal
at the high spots. Dunno which is faster.

>
>> Very. Softer than Sn63 solder by a lot. It's often used as the O-ring
>> in cryostats.
>
> Good. I'll add it to my short list. If it works, management can then
> declare it too expensive, leaving me with what I originally wanted to
> use as the winner. (red herring).
>
>> Yep, but solar cells have to run cooler, because you lose power output
>> really badly otherwise--the series resistance goes up and the open
>> circuit voltage drops.
>
> True, but ignoring the operating temperatures, comparing the thermal
> resistances of the quilted indium foil with my tinkering is all I
> wanted.
>
> Please note that my testing of thermal pastes and assembly methods
> were not exactly an organized project. I was trying to solve output
> power variability problems in production as well as squeeze a few more
> watts out of the available components to score a few points with
> marketing. It was by no means an organized effort and was spread over
> about 5 years of development on multiple products. Testing was
> resumed many years later when I entered the computer repair biz, and
> once again ran into the mysticism and magic that seems to surround
> thermal management.

You got that right.

[Michael A. Terrell]

John Larkin wrote:
>
> It often makes sense to use more semiconductors and spread the heat
> out. That's easy at low frequencies, harder at RF.

Really? They have been building high power solid state transmitters
for decades. Harris was building a 5 KW AM broadcast transmitter with
FETs in TO3 cases in the late '80s. It is needless to say this but they
had to redesign the modules, when they stopped manufacturing transistors
in the TO3 package.

Now, you can buy a UHF TV transmitter that will put out as much power
as you can afford. They build standardized modules that are fed from a
power divider, then the outputs go into a power combiner. The
transmitter has an embedded computer system to monitor the system. It
will report the total power out, reflected power and it will tell the
operator if one of the RF trays fails, along with which tray is bad.

[Bill Beaty]

On Monday, December 14, 2015 at 8:11:19 AM UTC-8, Jeff Liebermann wrote:
> Solder also isn't that wonderful a thermal conductor, even with silver
> added:
> <http://www.electronics-cooling.com/2006/08/thermal-conductivity-of-solders/>

Huh? Read again, looks like 5,000x better than thermal grease.

That's millikelvins, not K.

> I'm looking for thermal paste with the highest possible conductivity,

Solid metal is a bit higher than silicone oil. By ~three orders.

> For example, I won't be looking into brazing or soldering the copper
> transistor base to the aluminum heat sink because the process will
> probably destroy the transistor junctions and warp the heat sink.

Room temp solder overheats transistors? Or 50C solder? "Low temp
solder" is below 100C. Indium-gallium type melts in your hand.
Using normal tin-lead would be silly. But low-temp solder might
not be stable against aluminum

[Jeff Liebermann]

On Mon, 14 Dec 2015 15:27:45 -0500, "Michael A. Terrell"
<mike.t...@earthlink.net> wrote:

>John Larkin wrote:
>>
>> It often makes sense to use more semiconductors and spread the heat
>> out. That's easy at low frequencies, harder at RF.

>Really? They have been building high power solid state transmitters
>for decades. Harris was building a 5 KW AM broadcast transmitter with
>FETs in TO3 cases in the late '80s. It is needless to say this but they
>had to redesign the modules, when they stopped manufacturing transistors
>in the TO3 package.

Yep.
<http://www.nautel.com/solutions/am-nx-series-25-50kw/>
<http://www.nautel.com/solutions/high-power-mw-nx-series-100kw-2mw/>
Notice the 85 to 90% efficiency on AM. Basically, it's a collection
of Class D switchers running 2.5kW at the carrier frequency. That
much better than the old daze of class A and AB where one was lucky to
get 35% efficiency.

> Now, you can buy a UHF TV transmitter that will put out as much power
>as you can afford. They build standardized modules that are fed from a
>power divider, then the outputs go into a power combiner. The
>transmitter has an embedded computer system to monitor the system. It
>will report the total power out, reflected power and it will tell the
>operator if one of the RF trays fails, along with which tray is bad.

TV efficiency is not so good running in the 20-25% range:
<http://www.nautel.com/wp-content/uploads/dlm_uploads/2012/08/NT-Series-Br-1.7-Mar2015-v2-web.pdf>
See chart at bottom of page. Drop another 5-15% depending on the
output filtering and/or combinging.

Ok, back to partying. It's a tough job, but someone has to do it.

[Jeff Liebermann]

On Mon, 14 Dec 2015 14:25:09 -0800 (PST), Bill Beaty
<bi...@eskimo.com> wrote:

>On Monday, December 14, 2015 at 8:11:19 AM UTC-8, Jeff Liebermann wrote:
>> Solder also isn't that wonderful a thermal conductor, even with silver
>> added:
>> <http://www.electronics-cooling.com/2006/08/thermal-conductivity-of-solders/>
>
>Huh? Read again, looks like 5,000x better than thermal grease.
>That's millikelvins, not K.

Nope. Thermal conductivity, in SI units, is in
Watts per meter-Kelvins
W/m-K
W/m/K
W/m·K
See:
<https://en.wikipedia.org/wiki/Thermal_conductivity#Units_of_thermal_conductivity>
<https://answers.yahoo.com/question/index?qid=20100412190941AAxekZD>

I can see where you got that idea. Many typesetters leave out the
multiply sign resulting in W/mK or milli-Kelvins.
<https://www.google.com/#q=w%2FmK>

11th commandment: Thou shalt not abrev.

>> I'm looking for thermal paste with the highest possible conductivity,
>
>Solid metal is a bit higher than silicone oil. By ~three orders.

Yep. Silicone transformer oil is about 0.1 to 0.2 W/m-K. Aluminum is
about 200 W/m-K. However, mix some powdered metals or alumina with
the smallest amount of silicon grease needed to not make a huge mess,
and the resulting thermal conductivity might creep up to about 0.5
W/m-K. Phil Hobbs found some stuff that claimed 3.5 W/m-K. That's
about it for the greases. Metals are more interesting.
W/m*K
Diamond 1000
h-BN 600
c-BN 740
Silver 406
Copper 385
Gold 314
Aluminum 205
Graphite 200
Carbon 150
SiC 120
Brass 109

>> For example, I won't be looking into brazing or soldering the copper
>> transistor base to the aluminum heat sink because the process will
>> probably destroy the transistor junctions and warp the heat sink.

>Room temp solder overheats transistors? Or 50C solder? "Low temp
>solder" is below 100C. Indium-gallium type melts in your hand.
>Using normal tin-lead would be silly. But low-temp solder might
>not be stable against aluminum

None of the above. I was thinking of trying Alumiweld or one of the
other aluminum brazing or soldering rods. There's some debate as to
whether it's soldering or brazing.
<http://www.alumiweld.com>
<http://www.instructables.com/id/Quick-and-easy-brazing-aluminum-copper-and-nonfer/>
The problem is that the brazing or soldering temperature for aluminum
is high enough to damage the transistor and warp the heat sink. Still,
it's tempting.

Ok, back to the party...

[tabb...@gmail.com]

On Monday, 14 December 2015 17:27:50 UTC, Jeff Liebermann wrote:


> Good. I'll add it to my short list. If it works, management can then
> declare it too expensive, leaving me with what I originally wanted to
> use as the winner. (red herring).

Don't herrings smell after a while? Still, I bet the contract doesn't specify odour limits.


NT

[Jeff Liebermann]

Yep. One of my favorite munchies is "raw" (actually lightly pickled)
herring with onions and pickles. I like it smoked (which is where the
red color comes from), but it's difficult to find in California. This
dish produces the ultimate dragon breath, which is useful for ending
meetings quickly, and repelling undesirable visitors to my office. The
effect lingers for hours so a little goes a long way. Tastes good
too.

I wasn't very serious about using a red herring in my next project.
I've been doing mostly design reviews, and analyzing science fiction
product proposals. I doubt if any company would trust me to design
anything that actually needs to work. Still, if they're foolish
enough to do so, I would probably include some obviously bad idea or
useless feature, that invites instant criticism and eventual deletion.
The managers, having satisfied their compulsion to kill off some part
of the project, will then not bother me.

[Spehro Pefhany]

On Mon, 14 Dec 2015 12:01:43 -0500, the renowned Phil Hobbs
<pcdhSpamM...@electrooptical.net> wrote:

>
>Very. Softer than Sn63 solder by a lot. It's often used as the O-ring
>in cryostats.

Yup, it just squishes like putty.


--sp





--
Best regards,
Spehro Pefhany
Amazon link for AoE 3rd Edition: http://tinyurl.com/ntrpwu8
Microchip link for 2015 Masters in Phoenix: http://tinyurl.com/l7g2k48

[Przemek Klosowski]

On Tue, 15 Dec 2015 03:12:31 -0500, Spehro Pefhany wrote:

> On Mon, 14 Dec 2015 12:01:43 -0500, the renowned Phil Hobbs
> <pcdhSpamM...@electrooptical.net> wrote:
>
>
>>Very. Softer than Sn63 solder by a lot. It's often used as the O-ring
>>in cryostats.
>
> Yup, it just squishes like putty.

Yup, essentially forms metal joints at room temperature on contact
pressure. To create a gas-tight O-ring, you just overlap the ends and
squeeze. If only other materials worked this way :)

[Neon John]

On Sun, 13 Dec 2015 09:58:25 -0800, John Larkin
<jjla...@highlandtechnology.com> wrote:

>
>Kapton has a high thermal resistance, maybe OK if it's really thin.

Thin enough that the whole joint measures 0.23 deg C/W.
>
>The phase-change stuff that I've tried was terrible, because it was
>thick and didn't really flow out from under the part. There's probably
>better stuff around. If it really liquifies and flows, it's probably
>OK.

The Laird stuff is hard to beat. You ought to get a sample and try
it. I buy it in pre-cut strips the height of the TO247 plus a little
and the length of the area the array of transistors mount to using
MaxClips. That makes assembly trivially easy.

>
>If you need low theta and insulation, you might consider a thin slab
>of lapped AlN and grease or epoxy. I'm seeing prices like $1.50 for a
>TO247-size piece, 10 or 15 mils thick. Of if the voltage is low,
>under 100 volts maybe, grease over 1 mil thick hard anodize, as the
>Decadent guy suggests.

Where might I find this stuff? I've looked around a little and have
had no luck. The peak voltage is around 1200 so the hard anodizing is
out.

>
>If thing get hardcore, use a copper heat spreader and grease, and bolt
>the copper to an anodized aluminum heat sink. That will do good
>lateral heat spreading, which can be the bottleneck with aluminum. The
>spreader magnifies the area of the insulator, too.

Tried that. The geometry isn't very favorable. It helped things a
bit but moving from mica and grease to the Laird stuff helped more
than anything I've tried so far.

>
>I want blocks of solid isotopically-pure diamond. I wonder why diamond
>is so hard to make.

A couple of decades ago I was over at the Research Triangle in NC with
a colleague. He stopped in to visit a colleague from another job.
This guy was growing monocrystaline transparent diamond using nothing
more than a water chilled block of copper and an acetylene torch set
to "smoke".

A linear actuator moved the copper block back and forth at about a
stroke a second over maybe 4 inches. The just-barely-sooty flame
played over the block at an angle.

It looked like a large heap of soot was deposited but after a couple
of days he could reach into the pile with tweezers and pull out a
sheet of pure diamond.

That's all I know about the process. He probably got a patent.

[John Larkin]

On Fri, 18 Dec 2015 14:27:55 -0500, Neon John <n...@never.com> wrote:

>On Sun, 13 Dec 2015 09:58:25 -0800, John Larkin
><jjla...@highlandtechnology.com> wrote:
>
>>
>>Kapton has a high thermal resistance, maybe OK if it's really thin.
>
>Thin enough that the whole joint measures 0.23 deg C/W.
>>
>>The phase-change stuff that I've tried was terrible, because it was
>>thick and didn't really flow out from under the part. There's probably
>>better stuff around. If it really liquifies and flows, it's probably
>>OK.
>
>The Laird stuff is hard to beat. You ought to get a sample and try
>it. I buy it in pre-cut strips the height of the TO247 plus a little
>and the length of the area the array of transistors mount to using
>MaxClips. That makes assembly trivially easy.
>
>>
>>If you need low theta and insulation, you might consider a thin slab
>>of lapped AlN and grease or epoxy. I'm seeing prices like $1.50 for a
>>TO247-size piece, 10 or 15 mils thick. Of if the voltage is low,
>>under 100 volts maybe, grease over 1 mil thick hard anodize, as the
>>Decadent guy suggests.
>
>Where might I find this stuff? I've looked around a little and have
>had no luck. The peak voltage is around 1200 so the hard anodizing is
>out.

Right, the anodize isn't safe much over 100 volts.


Most of the AlN people seem dedicated to not selling parts. I did have
good response, and some nice samples, from www.siennatech.com. Ask for
Karen. Say hi for me.

>
>>
>>If thing get hardcore, use a copper heat spreader and grease, and bolt
>>the copper to an anodized aluminum heat sink. That will do good
>>lateral heat spreading, which can be the bottleneck with aluminum. The
>>spreader magnifies the area of the insulator, too.
>
>Tried that. The geometry isn't very favorable. It helped things a
>bit but moving from mica and grease to the Laird stuff helped more
>than anything I've tried so far.
>
>>
>>I want blocks of solid isotopically-pure diamond. I wonder why diamond
>>is so hard to make.
>
>A couple of decades ago I was over at the Research Triangle in NC with
>a colleague. He stopped in to visit a colleague from another job.
>This guy was growing monocrystaline transparent diamond using nothing
>more than a water chilled block of copper and an acetylene torch set
>to "smoke".
>
>A linear actuator moved the copper block back and forth at about a
>stroke a second over maybe 4 inches. The just-barely-sooty flame
>played over the block at an angle.
>
>It looked like a large heap of soot was deposited but after a couple
>of days he could reach into the pile with tweezers and pull out a
>sheet of pure diamond.
>
>That's all I know about the process. He probably got a patent.

Or DeBeers disappeared him.

[Jasen Betts]

IMO brazing is soldering using a bronze filler.

><http://www.alumiweld.com>
><http://www.instructables.com/id/Quick-and-easy-brazing-aluminum-copper-and-nonfer/>
> The problem is that the brazing or soldering temperature for aluminum
> is high enough to damage the transistor and warp the heat sink. Still,
> it's tempting.

solder a copper plate to the heatsink using the special solder and then use ordinary, or
low temperture solder to attach the transistor to that.

--
\_(ツ)_

[sean....@gmail.com]

Al foil seems like a good fill to me. Or gold leaf if surface is flat to a few microns anyway. But that's only my idea, you would have to prove it out in a lab.

[David Eather]

I don't know what the noise about gold is for - it has worse thermal
properties than silver and cost heaps more

[DecadentLinuxUserNumeroUno]

On Mon, 21 Dec 2015 06:27:10 +1000, "David Eather" <eat...@tpg.com.au>
Gave us:

Silver filled epoxy. Takes up ANY gap so the fit about how conformal
Gold foil can be is moot. The diamond powder stuff is better though.
Diamond beats all metals on thermal.

[Jeff Liebermann]

On Mon, 21 Dec 2015 06:27:10 +1000, "David Eather" <eat...@tpg.com.au>

wrote:

List of candidates and typical thermal conductivity:
W/m*K
Diamond 1000
h-BN 600 (Boron Nitride)
c-BN 740 (Cubic Boron Nitride)

Silver 406
Copper 385
Gold 314
Aluminum 205
Graphite 200
Carbon 150
SiC 120
Brass 109

Indium 86
Arctic Ag paste 5
Dow Corning 340 0.54

Gold is very malleable and can be pounded into extremely thin sheets
(gold leaf), while silver cannot do this. The idea is for the gold
leaf to act in place of the silicon goo, and only fill in the cracks
and gouges, not act as a shim, which prevents metal to metal contact
between the heat sink and the xsistor base. Phil Hobbs countered that
gold leaf likes to dissolve into the base metals and disappear, which
might actually be an advantage if it leaves some metal behind in the
cracks. However, I haven't tried it yet, so I don't know what it
takes to make it work. One thing for sure. Handling gold leaf will
likely become a production nightmare.

More:
"Silicone Grease Solutions For Your Thermal Interface Needs"
<https://www.dowcorning.com/content/publishedlit/11-1712-01.pdf>

[David Eather]

On Mon, 21 Dec 2015 08:05:37 +1000, Jeff Liebermann <je...@cruzio.com>

I used to guild as a hobby. I assure you that silver can indeed be pounded
into this sheets - but 24 caret gold is much softer which is probably the
property they needed here

[Jeff Liebermann]

On Tue, 22 Dec 2015 07:54:21 +1000, "David Eather" <eat...@tpg.com.au>
wrote:

>I used to guild as a hobby. I assure you that silver can indeed be pounded
>into this sheets - but 24 caret gold is much softer which is probably the
>property they needed here

Foiled again (pardon the pun).

I scraped these thicknesses numbers from an assortment of web sites
offering to sell the stuff. I picked what I think are the most common
thicknesses, but could use some corrections. I don't understand why
the fake silver (Al) leaf is so much thicker than the real aluminum
leaf.

Microns
Fake silver 1.8 (Al)
Silver leaf 0.3 to 0.5
Fake gold leaf 0.3 to 0.6 (85% Cu, 15% Zn)
Gold leaf 0.13
Aluminum leaf 0.8 to 4.0

It might be worth trying to use silver leaf as a TIM (thermal
interface material).
<http://www.ebay.com/itm/272064693008>
<http://www.ebay.com/itm/272050223614>

Ymmm... edible gold leaf:
<http://stores.ebay.com/Picasso-Frame-Depot/EIDBLE-GOLD-LEAF-FOOD-DECOR-/_i.html?_fsub=9752329010>

Thanks.

[George Herold]

One thing I don't see discussed much is the effect of pressure.
How hard you are squeezing the two materials together.
No filler was involved, but I did some testing of
brass 1/4 inch standoffs and the contact resistance
at each end changed a lot depending on how tightly
it was screwed down. I'd have to check notes, but contact resistance
was 1/2 to maybe twice the resistance of the brass piece.

George H.

[DecadentLinuxUserNumeroUno]

On Sun, 20 Dec 2015 14:05:37 -0800, Jeff Liebermann <je...@cruzio.com>
Gave us:

snip

My idea about graphene is spot on. I found this:

http://www.graphenea.com/pages/graphene-properties#.Vnll4Fm2t_k

[Clifford Heath]

On 22/12/15 08:54, David Eather wrote:
> I used to guild as a hobby

I think you mean gild. Unless you're in a gilding guild :).

[Jeff Liebermann]

On Tue, 22 Dec 2015 16:43:09 -0500, DecadentLinuxUserNumeroUno
<DL...@DecadentLinuxUser.org> wrote:

> My idea about graphene is spot on. I found this:
>http://www.graphenea.com/pages/graphene-properties#.Vnll4Fm2t_k

I see no idea, how graphene is suppose to produce a superior thermal
interface, or how a 1 atom layer of graphene will fill a much wider
gap between a power device and a heat sink. Please elaborate (or
labor at any rate).

<https://en.wikipedia.org/wiki/Graphene#Thermal_conductivity>
I don't understand everything in the thermal section of the article.
However, I do note that coating a one atom layer of graphene on
something else reduces the thermal conductivity to about 500-600
W/m-K, which is about the same as much cheaper graphite. I see no
benefit to using graphene as a TIM (thermal interface material).

[Jeff Liebermann]

On Tue, 22 Dec 2015 09:03:42 -0800 (PST), George Herold
<ghe...@teachspin.com> wrote:

>One thing I don't see discussed much is the effect of pressure.
>How hard you are squeezing the two materials together.
>No filler was involved, but I did some testing of
>brass 1/4 inch standoffs and the contact resistance
>at each end changed a lot depending on how tightly
>it was screwed down. I'd have to check notes, but contact resistance
>was 1/2 to maybe twice the resistance of the brass piece.
>George H.

Pressure is important, but can also be a problem. What you're doing
by applying pressure are:
1. Compressing the TIM (thermal interface material) so that it fill
the cracks and gaps.
2. Exude any excess TIM goo out of the gap, to produce a thinner TIM.
3. Straightening the base metals if they are not perfectly flat.
4. Compressing the metals so that they mix (alloy) at the interface.
This probably takes more pressure than the typical heat sink can
provide, but it might be possible if the metals are plated with a
softer metal (gold or indium).

The idea behind a TIM is to *NOT* require that the heat sink be
applied under pressure. Instead, the imperfections in the metal parts
are filled by a thermal conductive paste, which requires only modest
pressure. Applying too much pressure to a ceramic case RF power
transistor or ceramic package CPU, will probably crack the case. In
laptops and some desktops, the heat sinks use coil springs and
shoulder screws to control the maximum pressure.

Your brass standoffs changed in contact resistance because the ends
were not flat or polished, which reduced the electrical contact area.
Half the bulk(?) resistance would imply half the contact area.

Like thermal resistance optimization, the objective is to maximize the
contact area. For thermal, I can use either conductive or
non-conductive paste or filler. For electrical, it has to be
conductive. For brass, I guess(tm) you could smear the end of the
standoff with solder paste, do the same to the other side, add flux,
shove a large DC current (AC causes spatter) through the joint, and
produce a soldered connection. If that's not good enough, think about
submerged arc welding. If that's too complexicated, think about
pounding the brass standoff into the base metal or heat sink using an
interference fit. If a PCB or sheet metal, use a swaged standoff:
<https://www.google.com/search?q=swage+standoff&tbm=isch>

[amdx]

On 12/20/2015 4:05 PM, Jeff Liebermann wrote:
> On Mon, 21 Dec 2015 06:27:10 +1000, "David Eather" <eat...@tpg.com.au>
> wrote:
>
>> On Mon, 21 Dec 2015 01:37:01 +1000, <sean....@gmail.com> wrote:
>>
>>> Al foil seems like a good fill to me. Or gold leaf if surface is flat to
>>> a few microns anyway. But that's only my idea, you would have to prove
>>> it out in a lab.
>
>> I don't know what the noise about gold is for - it has worse thermal
>> properties than silver and cost heaps more
>
> List of candidates and typical thermal conductivity:
> W/m*K
> Diamond 1000
> h-BN 600 (Boron Nitride)
> c-BN 740 (Cubic Boron Nitride)
> Silver 406
> Copper 385
> Gold 314
> Aluminum 205
> Graphite 200
> Carbon 150
> SiC 120
> Brass 109
> Indium 86
> Arctic Ag paste 5

SiL-Pad 2000 3.5W/m.K
> Dow Corning 340 0.54

Just wanted to compare Sil-pad 2000

$75 for a 6" x 6" sheet, sheesh.

> http://www.newark.com/bergquist/sil-pad-2000-150mmx150mm-sheet/thermally-conductive-insulator/dp/06WX5970?ost=06WX5970&ad=81515565981&selectedCategoryId=&CMP=KNC-GUSA-GEN-SHOPPING-NEW-BERGQUIST&gclid=COjq583g8MkCFdgTgQod5XEDYg

Mikek

[David Eather]

On Wed, 23 Dec 2015 09:41:48 +1000, Clifford Heath <no....@please.net>
wrote:

> On 22/12/15 08:54, David Eather wrote:
>> I used to guild as a hobby
>
> I think you mean gild. Unless you're in a gilding guild :).
>

i think i do mean gild - thanks

[Jeff Liebermann]

<http://www.bergquistcompany.com/thermal_materials/sil_pad/sil-pad-2000.htm>
<http://www.bergquistcompany.com/pdfs/dataSheets/PDS_SP%202000_HENKEL%200615.pdf>
<http://www.farnell.com/datasheets/49499.pdf>

That's some form of BN (boron nitride) suspended in silicone rubber
with fiberglass threads to hold it together. You start off with a
thermal conductivity of 600 or 740 W/m-K for the BN, and end up with
3.5 W/m-K after adding the silicone rubber. The problem is getting
enough contact surface between the BN particles. Too much conctact
area, and the insulator becomes brittle and falls apart. If enough
silicone rubber is used to cover the BN particles, the insulator might
hold together, but the thermal conductivity is terrible. Even BN
powder, with no silicone rubber, doesn't work because the
incompressible BN granules form insulating air gaps.

Also, did you notice the price? $75 for one 150 x 150mm sheet. Ouch.

[DecadentLinuxUserNumeroUno]

On Tue, 22 Dec 2015 15:51:18 -0800, Jeff Liebermann <je...@cruzio.com>
Gave us:

>I see no idea, how graphene is suppose to produce a superior thermal
>interface, or how a 1 atom layer of graphene will fill a much wider
>gap between a power device and a heat sink. Please elaborate (or
>labor at any rate).

They were talking about making prophylactics from it too.. So they
*must* be able to make thicker sheets.

It is also a much bigger molecular lattice than the Helium atom is,
yet it will not all them to pass. They are talking about lining helium
airships with it to reduce the inevitable leakage which currently
occurs.

So I think it would make great ESD mats or one could impregnate carbon
nanotubes into thin Teflon sheets for that.

But yeah, I think there can be applications for thermal abatement
here.

You don't?

Is that elaborate enough (or at a high enough rate)?

[DecadentLinuxUserNumeroUno]

On Wed, 23 Dec 2015 10:57:41 +1000, "David Eather" <eat...@tpg.com.au>
Gave us:

That dirty pit nicker!

[Jeff Liebermann]

On Tue, 22 Dec 2015 20:52:44 -0500, DecadentLinuxUserNumeroUno
<DL...@DecadentLinuxUser.org> wrote:

>But yeah, I think there can be applications for thermal abatement
>here.
>
>You don't?

Well, I'm sure you could conjure some application that might involve
moving heat from here to there via graphene. However, for the
immediate problem of finding the best TIM (thermal interface material)
for RF power transistors and aluminum heat sinks, graphene is not a
candidate.

> Is that elaborate enough (or at a high enough rate)?

Hardly. What's missing are numbers, calcs, references, URL's,
buzzwords, acronyms, and other devices that allow me to distinguish
between a likely fact and your opinion. You are of course entitled to
pass judgement, offer an opinion, and inflict both upon this
newsgroup. However, without substantiation, methinks opinions,
pontifications, and judgements are generally worthless. In this case,
how would you use graphene as a TIM and show some examples or prior
art. If the idea is totally new, produce some numbers that might
suggest that it's possible.

However, you got me thinking again about using graphic powder (not
flakes). No need for graphene here. If I smear some graphite powder
on both the power transistor and the heat sink, the cracks will mostly
fill with the powder. I can then scrape off the excess and rub the
power transistor onto the heatsink in a figure 8 (which someone
suggested previously), which should remove any excess graphite (if the
surfaces are reasonably flat). It will also make a huge mess, but
that can be cleaned later.

[DecadentLinuxUserNumeroUno]

On Tue, 22 Dec 2015 18:25:53 -0800, Jeff Liebermann <je...@cruzio.com>
Gave us:

>between a likely fact and your opinion.

Referencing that someone mentioned making a prophylactic from it was
not an opinion.

Also., here is a top research facility talking about using it.

https://www.google.com/?gws_rd=ssl#q=darpa+uses+graphene+as+a+heat+sink+compound

[mixed nuts]

Cosmetic grade BN powder isn't as messy. And you can get it in
different colors.

--
Grizzly H.

[George Herold]

Hi Jeff, sorry my posts suffer from not enough information sometimes.
I was using brass standoffs as "weak" thermal links from a ln2 bath to
a sample stage. You can calculate what the thermal resistance should be.
And what I found was that the measured thermal resistance was something like
twice the calculated value to (maybe) four times bigger. Depending on
how hard the screws were tightened. I assumed the extra resistance was
the contact/ surface resistance... (the thing you are trying to reduce with the
TIM) And since there were two surfaces I apportioned the extra resistance equally
to each side... hence my 1/2 to twice value. I should have tried some goop at
the interface and measured the change.. but I didn't... Maybe next time.

George H.

[Phil Hobbs]

On 12/13/2015 11:16 AM, Phil Hobbs wrote:
> On 12/12/2015 10:21 PM, Jeff Liebermann wrote:
>> On Sat, 12 Dec 2015 16:39:32 -0800 (PST), tabb...@gmail.com wrote:
>>
>>> What, you didn't try toothpaste? :)
>>
>> If I repeated the tests today, I wouldn't bother with toothpaste.
>> Toothpaste is 20-42% water, which has a lousy thermal conductivity
>> (0.6 W/m-K). If I evaporated the water AFTER installing, there will
>> be air gaps. No thanks.
>>
>> Instead, I would try gold leaf (314 W/m-k) again and add flake
>> graphite (750 W/m-K):
>> "THERMAL CONDUCTIVITY OF GRAPHITE FLAKE COMPOSITES"
>> <http://acs.omnibooksonline.com/data/papers/2007_C081.pdf>
>>
>> Also, note that the differences between the various compounds is in
>> the area of 0.1 C/Watt. That doesn't seem like much until you try to
>> dissipate 150 watts per device:
>> 0.1 * 150 = 15 C
>> which can be the difference between running hot and meltdown.
>>
>
> Some friends of mine developed a couple of interesting technologies for
> metallic thermal interface materials (TIMs). One is an indium-gallium
> liquid alloy that was used in some higher end Apple machines. It works
> the best of anything, but is vulnerable to corrosion. The other is
> indium foil with a very small quilt pattern embossed in it. Both work
> dramatically better than the best paste. The quilt pattern allows the
> metal to conform better to the surfaces, because it only has to flow a
> short distance to get out from under a high spot. Either one is good
> enough for a 2500-sun solar concentrator--in fact it was the metal TIM
> that made the concentrator possible. (I did a little work on the solar
> project, but not on the TIMs, except to cheer from the sidelines.)
>
> The best paste as of 2007ish came in at about 3.5 W/m/K. It was made by
> a Japanese outfit whose name I forget--it had tiny flat metal flakes in
> it, which were supposed to form stacks so that most of the heat went
> through a solid metal path. It turned out that the stacks performed
> worst under temperature cycling. Since the stacks were pinned in place,
> expansion of the grease washed the small particles out from between the
> flakes, which dramatically increased the thermal resistance.
>
> Cheers
>
> Phil Hobbs
>

Finally remembered. The paste I was thinking of was some special Shin
Etsu stuff, around 4.5-5 W/m/K.

Cheers

Phil Hobbs

--
Dr Philip C D Hobbs
Principal Consultant
ElectroOptical Innovations LLC
Optics, Electro-optics, Photonics, Analog Electronics

160 North State Road #203
Briarcliff Manor NY 10510

hobbs at electrooptical dot net
http://electrooptical.net

[dca...@krl.org]

On Tuesday, December 22, 2015 at 8:41:06 PM UTC-5, Jeff Liebermann wrote:

> >> List of candidates and typical thermal conductivity:
> >> W/m*K
> >> Diamond 1000
> >> h-BN 600 (Boron Nitride)
> >> c-BN 740 (Cubic Boron Nitride)
> >> Silver 406
> >> Copper 385
> >> Gold 314
> >> Aluminum 205
> >> Graphite 200
> >> Carbon 150
> >> SiC 120
> >> Brass 109
> >> Indium 86
> >> Arctic Ag paste 5
> >SiL-Pad 2000 3.5W/m.K
> >> Dow Corning 340 0.54
>

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

https://www.chemtronics.com/c-280-circuitworks-heat-sink-greases.aspx

CircuitWorks® Boron Nitride Heat Sink Grease facilitates heat transfer away from electrical/electronic components and into heat sinks. The material exhibits exceptionally high thermal conductivity with outstanding dielectric properties.

In case you did not know about this grease.

CircuitWorks® Boron Nitride Heat Sink Grease facilitates heat transfer away from electrical/electronic components and into heat sinks. The material exhibits exceptionally high thermal conductivity with outstanding dielectric properties.

[John Larkin]

Dow has some grease that's around 4.

http://tinyurl.com/hxhhe5v

They claim anti-pump-out too.

--

John Larkin Highland Technology, Inc

lunatic fringe electronics

[Jeff Liebermann]

On Wed, 23 Dec 2015 11:42:15 -0500, Phil Hobbs
<pcdhSpamM...@electrooptical.net> wrote:

Thanks. Looks like they have taken it to market:
<https://www.microsi.com/product/g751/>
<https://www.microsi.com/wp-content/uploads/2015/06/G751TDS-1202015.pdf>
<https://www.microsi.com/product-category/packaging/thermal-grease/>
<www.amazon.com/MASSCOOL-Shin-Etsu-Interface-Material-G751/dp/B000S35TB4/>
Claims 4.5 W/m-K so it might be the same or similar stuff.

I don't have a clue what's in it, except that it looks, smells, and
works much like Arctic Silver, which contains a little of everything
(silver, boron, alumina, zinc oxide, etc). However, Artic Silver
claims 8.7 W/m-K while NREL tests show only 0.89 W/m-K.
<http://www.nrel.gov/docs/fy08osti/42972.pdf>
Interesting reading and quite a list of different magic formulas. The
winner was Dow Corning TC-5022 at 4.0 W/m-K. Second best was Shinetsu
X-23-7762-S at 3.7 W/m-K (claimed 4.0).

None of the greases even come close to the dry flake, powder, and foil
thermal conductivity numbers. Obviously, pastes are easier to handle,
but with a potential 100:1 performance benefit, it would seem that the
dry TIMs would be worth investigating.

Bah Humbug (T'is the season, so I can say that).

[Jeff Liebermann]

On Wed, 23 Dec 2015 09:11:59 -0800 (PST), "dca...@krl.org"
<dca...@krl.org> wrote:

>On Tuesday, December 22, 2015 at 8:41:06 PM UTC-5, Jeff Liebermann wrote:
>
>> >> List of candidates and typical thermal conductivity:
>> >> W/m*K
>> >> Diamond 1000
>> >> h-BN 600 (Boron Nitride)
>> >> c-BN 740 (Cubic Boron Nitride)
>> >> Silver 406
>> >> Copper 385
>> >> Gold 314
>> >> Aluminum 205
>> >> Graphite 200
>> >> Carbon 150
>> >> SiC 120
>> >> Brass 109
>> >> Indium 86
>> >> Arctic Ag paste 5
>> >SiL-Pad 2000 3.5W/m.K
>> >> Dow Corning 340 0.54

>https://www.chemtronics.com/c-280-circuitworks-heat-sink-greases.aspx

>In case you did not know about this grease.

>CircuitWorksŽ Boron Nitride Heat Sink Grease facilitates heat

>transfer away from electrical/electronic components and into
>heat sinks. The material exhibits exceptionally high thermal
>conductivity with outstanding dielectric properties.

The performance must be so outstanding that the company doesn't see a
need to supply any thermal conductivity numbers on their number-free
data sheets. The best I could find is "Exceeds MIL-C-47113 for
Thermal Conductivity":
<https://www.chemtronics.com/p-691-circuitworks-boron-nitride-heat-sink-grease.aspx>
Oddly, the MSDS sheet only mentions that it contains "Silica,
amorphous, fumed, cryst.-free".
<https://www.chemtronics.com/descriptions/document/CW7250_ISS%20MSDS%20North%20America%20(ANSI%20Z400.1)%20V4.3.2%20-%20United%20States%20of%20America_English%20(US).pdf>
Looks like it's not pure and expensive BN (boron nitride) but is
rather a mix of cheaper conductive powders with a little BN added.
Little wonder there are no numbers or test results.

[Jeff Liebermann]

On Tue, 22 Dec 2015 23:09:35 -0500, DecadentLinuxUserNumeroUno
<DL...@DecadentLinuxUser.org> wrote:

>On Tue, 22 Dec 2015 18:25:53 -0800, Jeff Liebermann <je...@cruzio.com>
>Gave us:
>
>>between a likely fact and your opinion.
>
> Referencing that someone mentioned making a prophylactic from it was
>not an opinion.

I didn't see that, but congratulations on having read what I posted.
Unfortunately, there's no mention in your comments on how a graphene
based TIM is going to solve the problem of filling cracks, and
reducing gaps in my RF power device heat sinks. I can see some
possibilities for moving heat from the transistor die, but not between
the package and the aluminum heat sink. Keep trying. It's a topic of
interest to me.

> Also., here is a top research facility talking about using it.
>https://www.google.com/?gws_rd=ssl#q=darpa+uses+graphene+as+a+heat+sink+compound

Ummm... I get a list of URL's. Any particular URL that I should be
reading? If you read the article, did it give a number for thermal
conductivity achievable in the lab?

<http://www.extremetech.com/extreme/175457-this-carbon-nanotube-heatsink-is-six-times-more-thermally-conductive-could-trigger-a-revolution-in-cpu-clock-speeds>
Carbon nanotubes have long been known to have amazing
thermal conductivity, but bonding them to thermal
interfaces has been problematic.
That's exactly the problem we're discussing. The carbon nanotube may
be a great thermal conductor, but if it can't connect to the device,
package, or heat sink, it's useless. Besides, if finding the material
with the best thermal conductivity were the only parameter of
importance, we would be using thermal paste made with diamond powder
or maybe diamond films.

[Jeff Liebermann]

On Tue, 22 Dec 2015 23:30:57 -0500, mixed nuts
<melops...@undulatus.budgie> wrote:

>Cosmetic grade BN powder isn't as messy. And you can get it in
>different colors.

Thanks. I didn't know that there was a cosmetic flavor. The h-BN
type forms flakes, which are the best for thermal conductivity. I'll
try not to think about the minimum purchase quantity and price:
<http://www.bn.saint-gobain.com/tres-bn-cosmetic-powders.aspx>
<http://www.bn.saint-gobain.com/uploadedFiles/SGbn/Documents/TRES_BN/TresBN-CosmeticPowders-ds.pdf>

List of candidates and typical 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
Aluminum 205
Graphite 200
Carbon 150
SiC 120
Brass 109
Indium 86

Pastes 4.0
SilPad 2000 3.5
Dow Corning 340 0.54

[DecadentLinuxUserNumeroUno]

On Wed, 23 Dec 2015 10:34:03 -0800, Jeff Liebermann <je...@cruzio.com>
Gave us:

>Ummm... I get a list of URL's.

The DARPA links. Remember what I wrote? "Top researchers". How many
of those do you think there are?

[mixed nuts]

On 12/23/2015 1:48 PM, Jeff Liebermann wrote:
> On Tue, 22 Dec 2015 23:30:57 -0500, mixed nuts
> <melops...@undulatus.budgie> wrote:
>
>> Cosmetic grade BN powder isn't as messy. And you can get it in
>> different colors.
>
> Thanks. I didn't know that there was a cosmetic flavor. The h-BN
> type forms flakes, which are the best for thermal conductivity. I'll
> try not to think about the minimum purchase quantity and price:
> <http://www.bn.saint-gobain.com/tres-bn-cosmetic-powders.aspx>
> <http://www.bn.saint-gobain.com/uploadedFiles/SGbn/Documents/TRES_BN/TresBN-CosmeticPowders-ds.pdf>

This is likely the right stuff:

http://www.mcmaster.com/#10515k68/

Then the real problem becomes: "What does one do with the other 127 oz?"

--
Grizzly H.

[Jeff Liebermann]

On Wed, 23 Dec 2015 06:51:55 -0800 (PST), George Herold
<ghe...@teachspin.com> wrote:

>Hi Jeff, sorry my posts suffer from not enough information sometimes.

Yeah, it happens, but as you mention, the contact area problems are
the same. By tightening the screw, you're increasing the area of the
contact patch, eliminating any air gaps, and crushing any rounded
granules into something flat. You could do better with a hammer or a
hydraulic press.

LN2 would be 77K, which is above the temperature where alloys and
impurities dominate the resistance of brass. Still, it might be worth
checking to see if the resistance/temp is still linear at 77K.
<http://www.radio-electronics.com/info/formulae/resistance/resistance-temperature-coefficient.php>

>I was using brass standoffs as "weak" thermal links from a ln2 bath to
>a sample stage. You can calculate what the thermal resistance should be.
>And what I found was that the measured thermal resistance was something like
>twice the calculated value to (maybe) four times bigger. Depending on
>how hard the screws were tightened. I assumed the extra resistance was
>the contact/ surface resistance... (the thing you are trying to reduce with the
>TIM) And since there were two surfaces I apportioned the extra resistance equally
>to each side... hence my 1/2 to twice value. I should have tried some goop at
>the interface and measured the change.. but I didn't... Maybe next time.

I think conventional thermal goo would have made it worse. You didn't
disclose the mechanics of your (microscope?) (aluminum?) sample stage.
If it's been machined reasonably flat, and isn't coated, plated, or
painted with something thermally disgusting, then simply machining and
polishing the end of the brass standoff should have produced good
results without super-tightening the screw. If my guess(tm) is
correct, adding some dust to fill in the imperfections, from my list
of TIM candidates, might improve things.

Disclaimer: My very limited cryogenics experience was in about 1980
making ice cream with liquid nitrogen, so please assume that I don't
have a clue what I'm doing or am seriously out of date.

[Jeff Liebermann]

I guess I'm among the "top researchers". First, I search. Then, I do
it again which is called re-search. I usually start at the top and
work my way down. That makes me a "top re-searcher" (after the 2nd
search). I don't know how many "top re-searchers" there might be.
Probably everyone that refine their searches starting from the top.

However, you're right about one thing. I forgot what you wrote. If
you want to prevent that from happening in the future, I suggest you
write something worth remembering. Try to reverse our positions. If
I wrote the above, would you even want to read it?

I'll look at the DARPA links after I recover from having three
Christmas lunches today. Too much of a good thing and far too much
chocolate. To recover, I'll be exercising more and fasting for at
least a week or three.

Drivel: Santa (almost) breaks the net:
<http://members.cruzio.com/~jeffl/poetry/stnick.htm>
I think I wrote that in about 1986, when the world population was
still around 5 billion. The technobabble is dated, but still
applicable. More:
<http://members.cruzio.com/~jeffl/poetry/poetry.htm>

Merry Christmas and Bah Humbug (T'is the season).

[dca...@krl.org]

On Wednesday, December 23, 2015 at 1:03:59 PM UTC-5, Jeff Liebermann wrote:

>
> The performance must be so outstanding that the company doesn't see a
> need to supply any thermal conductivity numbers on their number-free
> data sheets. The best I could find is "Exceeds MIL-C-47113 for
> Thermal Conductivity":
>

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

If you want boron nitride powder you might try

http://www.aliexpress.com/item/150g-Hexagonal-Boron-Nitride-Powde-Boron-Nitride-powder/32491205452.html?spm=2114.01020208.3.131.Fg1fH2&ws_ab_test=searchweb201556_6,searchweb201644_2_79_78_77_82_80_62_81,searchweb201560_1

150 grams for $15.97 including shipping.

Dan

[Jeff Liebermann]

On Wed, 23 Dec 2015 18:35:05 -0800 (PST), "dca...@krl.org"
<dca...@krl.org> wrote:

>On Wednesday, December 23, 2015 at 1:03:59 PM UTC-5, Jeff Liebermann wrote:
>> The performance must be so outstanding that the company doesn't see a
>> need to supply any thermal conductivity numbers on their number-free
>> data sheets. The best I could find is "Exceeds MIL-C-47113 for
>> Thermal Conductivity":

>If you want boron nitride powder you might try
>http://www.aliexpress.com/item/150g-Hexagonal-Boron-Nitride-Powde-Boron-Nitride-powder/32491205452.html

>150 grams for $15.97 including shipping.
> Dan

Thanks. I was looking at what was offered on eBay. Few specified the
grain size. I was hoping for 1 micron to fill the cracks, but the
above 5 to 10 micron grain size might be good enough. I'll probably
buy something after the Chrismas frenzy is over and I finish some
paying projects. Also flake graphite, which should be cheaper. Or
maybe some 1 micron diamond powder?
<http://www.aliexpress.com/item/20g-99-99-Diamond-Powder-Polishing-8000-0-1um-W1-Grit-Mesh-100Cts/32232076716.html>
Oh-oh. Yet another project.
--

[Jeff Liebermann]

On Wed, 23 Dec 2015 16:44:23 -0500, mixed nuts

<melops...@undulatus.budgie> wrote:

>On 12/23/2015 1:48 PM, Jeff Liebermann wrote:
>> On Tue, 22 Dec 2015 23:30:57 -0500, mixed nuts
>> <melops...@undulatus.budgie> wrote:
>>
>>> Cosmetic grade BN powder isn't as messy. And you can get it in
>>> different colors.
>>
>> Thanks. I didn't know that there was a cosmetic flavor. The h-BN
>> type forms flakes, which are the best for thermal conductivity. I'll
>> try not to think about the minimum purchase quantity and price:
>> <http://www.bn.saint-gobain.com/tres-bn-cosmetic-powders.aspx>
>> <http://www.bn.saint-gobain.com/uploadedFiles/SGbn/Documents/TRES_BN/TresBN-CosmeticPowders-ds.pdf>

>This is likely the right stuff:
>http://www.mcmaster.com/#10515k68/
>Then the real problem becomes: "What does one do with the other 127 oz?"

Nope. The real problem is that it's boron nitride based PAINT.
Methinks it's fairly apparent that the superior thermal conductivity
of any of the previously mentioned powders, it thoroughly ruined by
the addition of some kind of fluid, paste, goo, grease, oil, slime, or
whatever. No thanks.

[mixed nuts]

On 12/24/2015 11:50 AM, Jeff Liebermann wrote:
> On Wed, 23 Dec 2015 16:44:23 -0500, mixed nuts
> <melops...@undulatus.budgie> wrote:
>
>> On 12/23/2015 1:48 PM, Jeff Liebermann wrote:
>>> On Tue, 22 Dec 2015 23:30:57 -0500, mixed nuts
>>> <melops...@undulatus.budgie> wrote:
>>>
>>>> Cosmetic grade BN powder isn't as messy. And you can get it in
>>>> different colors.
>>>
>>> Thanks. I didn't know that there was a cosmetic flavor. The h-BN
>>> type forms flakes, which are the best for thermal conductivity. I'll
>>> try not to think about the minimum purchase quantity and price:
>>> <http://www.bn.saint-gobain.com/tres-bn-cosmetic-powders.aspx>
>>> <http://www.bn.saint-gobain.com/uploadedFiles/SGbn/Documents/TRES_BN/TresBN-CosmeticPowders-ds.pdf>
>
>> This is likely the right stuff:
>> http://www.mcmaster.com/#10515k68/
>> Then the real problem becomes: "What does one do with the other 127 oz?"
>
> Nope. The real problem is that it's boron nitride based PAINT.
> Methinks it's fairly apparent that the superior thermal conductivity
> of any of the previously mentioned powders, it thoroughly ruined by
> the addition of some kind of fluid, paste, goo, grease, oil, slime, or
> whatever. No thanks.

I think it's just packaged wet to avoid dusting with a little bentonite
clay pushed to alkaline with a little ammonia to form a colloidal
suspension. After the water goes away it'd be pretty fluffy - no
non-volatile organic binders, oil etc.

--
Grizzly H.

[Jeff Liebermann]

On Thu, 24 Dec 2015 12:25:23 -0500, mixed nuts

Nope. It seems rather odd when they can just bag the h-BN along with
an inert gas and not need the water carrier. The MSDS call it a
"paint":
<http://www.mcmaster.com/mvA/library/20120416/1735300%20gpc%20boron%20nitride%20040912.pdf>
Water 7732-18-5 60 - 100 %
Amine Coated Bentonite 68953-58-2 1 - 5 %
Boron nitride 10043-11-5 10 - 30 %
That's an awful lot of water for just a carrier. 100% water? How
does that work when there's nothing left for the h-BN?

However, you're probably right about suspending the h-BM particles in
solution since this suppose to be some kind of ceramic high
temperature lubricant. No data sheet, no clue on the grain size, and
no OEM part number.

Going to the source and digging through a web site obviously designed
as a work of art instead of information:
<http://www.momentive.com/categories/all-product-categories.aspx>
I find this under "paint":
<http://www.momentive.com/Categories/Ceramics/Boron-Nitride-Paints.aspx>
BN sprays feature high-purity, fine BN crystals suspended within
a fast-drying, solvent-based carrier formulation. Available
in 13-ounce aerosol cans and made available in 12-can carton
shipments, each BN spray can is able to provide about 100 square
feet of coverage and is designed to produce a smooth coating
with very low binder content.
Ok, it really is a paint, which the data sheets has morphed into a
"coating":
<http://www.momentive.com/WorkArea/DownloadAsset.aspx?id=27489>
Well, the applications mix are rather interesting, but nothing
involving high thermal conductivity. Also, no grain size, or how to
get rid of the residual bentonite clay. No thanks.

[dca...@krl.org]

On Thursday, December 24, 2015 at 7:08:19 PM UTC-5, Jeff Liebermann wrote:

> Ok, it really is a paint, which the data sheets has morphed into a
> "coating":

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

I think it is a mold release.

Dan

[DecadentLinuxUserNumeroUno]

On Fri, 25 Dec 2015 07:45:51 -0800 (PST), "dca...@krl.org"
<dca...@krl.org> Gave us:

Castle Wolfenstein!

[Jeff Liebermann]

On Fri, 25 Dec 2015 07:45:51 -0800 (PST), "dca...@krl.org"

<dca...@krl.org> wrote:

>On Thursday, December 24, 2015 at 7:08:19 PM UTC-5, Jeff Liebermann wrote:
>> Ok, it really is a paint, which the data sheets has morphed into a
>> "coating":

>I think it is a mold release.
> Dan

The spread of mold in my house has been successfully contained and
limited to the shower. I really don't want it released elsewhere in
the house (although I do like blue cheese mold).

[dca...@krl.org]

On Wednesday, December 23, 2015 at 1:03:59 PM UTC-5, Jeff Liebermann wrote:

> The performance must be so outstanding that the company doesn't see a
> need to supply any thermal conductivity numbers on their number-free
> data sheets. The best I could find is "Exceeds MIL-C-47113 for
> Thermal Conductivity":

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

I sent them a query on what is their actual thermal conductivity. Will post if I get an answer.

Dan