Heatsink, just don't drop it on concrete

Bottom posting. (Google here)

No insulator. Could glue a chip to it and have some advantages with that. Power transistor cases, much better than plastic and if you can get the silicon to stick to it you have a really good package.

In my opinion, ceramic is a bit too hard to machine for use as heat sinks per se. This stuff about near has to be molded to its shape the first time. With holes.

I wonder how brittle it really is. (was mentioned "drop it") Maybe I'll get one and find out. I do have a cement floor.

If I remember I might, got other things to do right now.

 

[John Larkin]

On Wed, 19 Jun 2019 22:13:18 -0700 (PDT), jurb6006@gmail.com wrote:

Bottom posting. (Google here)

No insulator. Could glue a chip to it and have some advantages with that. Power transistor cases, much better than plastic and if you can get the silicon to stick to it you have a really good package.

In my opinion, ceramic is a bit too hard to machine for use as heat sinks per se. This stuff about near has to be molded to its shape the first time. With holes.

I sure hope that the semi contact area is ground flat. Moulded ceramic
is usually rough, and roughness wrecks thermal conductivity. But I
guess that's not so important for a small heat sink.


--

John Larkin Highland Technology, Inc

lunatic fringe electronics

 

"Tim Williams" <tiwill@seventransistorlabs.com> wrote in
news:qeg3uj$8qr$1@dont-email.me:

"John Larkin" <jjlarkin@highlandtechnology.com> wrote in message
news:s92ngepq1qupotbukg6toj0hjrqt1u0d2u@4ax.com...
I sure hope that the semi contact area is ground flat. Moulded
ceramic is usually rough, and roughness wrecks thermal
conductivity. But I guess that's not so important for a small
heat sink.


If it's HIP like I suspect, the surface will be not only mirror
finish, but so smooth that you have little hope of getting a
strong epoxy bond, if you wished to glue to it.

Tim

His claim is false. A ROUGH surface degrades an interface. It
would have to be very rough though. The smoothness a cast or
moulded ceramic face has is far too fine grained a surface profile
for it to degrade thermal flow. And it will also allow adhesive
attachment a bit more.

And the other problem mirror finish has (for epoxy attachment) is
that if your epoxy detaches, it is as if it is not even attached at
all. Smoke ensues.

 

John Larkin <jjlarkin@highlandtechnology.com> wrote in
news:s92ngepq1qupotbukg6toj0hjrqt1u0d2u@4ax.com:

On Wed, 19 Jun 2019 22:13:18 -0700 (PDT), jurb6006@gmail.com
wrote:

Bottom posting. (Google here)

No insulator. Could glue a chip to it and have some advantages
with that. Power transistor cases, much better than plastic and if
you can get the silicon to stick to it you have a really good
package.

In my opinion, ceramic is a bit too hard to machine for use as
heat sinks per se. This stuff about near has to be molded to its
shape the first time. With holes.

I sure hope that the semi contact area is ground flat. Moulded
ceramic is usually rough, and roughness wrecks thermal
conductivity. But I guess that's not so important for a small heat
sink.

The flatness is what counts. Coplanarity is what is important
when mating the heat source to the sink.

No, surface texture at that level has ZERO effect for or against
heat flow. The interface is where most is lost, and that is about
the interface medium. Air = no good. So we put fillers in. sil-pad
tabs or liquid 'paste'.
The surface quality of molded ceramic is fine grained, and
presents exactly ZERO difference.

If it were actually 'rough' you would have a valid point. But the
profile of the texture of a molded ceramic face is far too fine to
have any effect against thermal flow.

IF it was ground with 36 grit. MAYBE. But the surface quality of
ceramic has zero effect. Far more important is a tight, flat
interface. Whereas the 36 grit ROUGH surface WOULD impede thermal
flow. But not really a lot. You said it "wrecks it" but it doesn't
really. Non-coplanarity does.

You could find out with your IR imager. The difference is
practically nil until the roughbess gets pretty far up there.

We had a guy who insisted on soldering the big FETs down before
mounting the heat sink. If they were individual sinks sure, but a
gang of 12 FETs across the edge of a board there to mate with a heat
sink poses problems with his method. We were frying FETs within
seconds of use. I showed him that we needed to mount the heat sink
and FET packages onto the PCB and THEN solder the FET legs.

 

[Tim Williams]

"John Larkin" <jjlarkin@highlandtechnology.com> wrote in message
news:s92ngepq1qupotbukg6toj0hjrqt1u0d2u@4ax.com...

I sure hope that the semi contact area is ground flat. Moulded ceramic
is usually rough, and roughness wrecks thermal conductivity. But I
guess that's not so important for a small heat sink.

If it's HIP like I suspect, the surface will be not only mirror finish, but
so smooth that you have little hope of getting a strong epoxy bond, if you
wished to glue to it.

Tim

--
Seven Transistor Labs, LLC
Electrical Engineering Consultation and Design
Website: https://www.seventransistorlabs.com/

 

[John Larkin]

On Thu, 20 Jun 2019 14:38:25 +0000 (UTC),
DecadentLinuxUserNumeroUno@decadence.org wrote:

John Larkin <jjlarkin@highlandtechnology.com> wrote in
news:s92ngepq1qupotbukg6toj0hjrqt1u0d2u@4ax.com:

On Wed, 19 Jun 2019 22:13:18 -0700 (PDT), jurb6006@gmail.com
wrote:

Bottom posting. (Google here)

No insulator. Could glue a chip to it and have some advantages
with that. Power transistor cases, much better than plastic and if
you can get the silicon to stick to it you have a really good
package.

In my opinion, ceramic is a bit too hard to machine for use as
heat sinks per se. This stuff about near has to be molded to its
shape the first time. With holes.

I sure hope that the semi contact area is ground flat. Moulded
ceramic is usually rough, and roughness wrecks thermal
conductivity. But I guess that's not so important for a small heat
sink.



The flatness is what counts. Coplanarity is what is important
when mating the heat source to the sink.

No, surface texture at that level has ZERO effect for or against
heat flow. The interface is where most is lost, and that is about
the interface medium. Air = no good. So we put fillers in. sil-pad
tabs or liquid 'paste'.
The surface quality of molded ceramic is fine grained, and
presents exactly ZERO difference.

If it were actually 'rough' you would have a valid point. But the
profile of the texture of a molded ceramic face is far too fine to
have any effect against thermal flow.

IF it was ground with 36 grit. MAYBE. But the surface quality of
ceramic has zero effect. Far more important is a tight, flat
interface. Whereas the 36 grit ROUGH surface WOULD impede thermal
flow. But not really a lot. You said it "wrecks it" but it doesn't
really. Non-coplanarity does.

You could find out with your IR imager. The difference is
practically nil until the roughbess gets pretty far up there.

We had a guy who insisted on soldering the big FETs down before
mounting the heat sink. If they were individual sinks sure, but a
gang of 12 FETs across the edge of a board there to mate with a heat
sink poses problems with his method. We were frying FETs within
seconds of use. I showed him that we needed to mount the heat sink
and FET packages onto the PCB and THEN solder the FET legs.

Both roughness and flatness matter for good heat conduction. Thermal
grease is not actually a very good heat conductor, and it needs to be
thin to minimize theta. If the contacting surfaces aren't flat and
smooth, that hurts. We machine aluminum extrusions flat for high power
stuff, because they tend to be wiggly as-extruded. Our ceramic AlN
insulators are lapped to basically optical limits. Transistor packages
tend to be very good.

Thermal silicone grease has ceramic filler particles, which may help
conduction but increases gap. They compress to below 100 microinches,
which is good. I tried some diamond filled grease, but the particles
were so big that they increased the gap, with no net benefit.



--

John Larkin Highland Technology, Inc

lunatic fringe electronics

 

John Larkin <jjlarkin@highlandtechnology.com> wrote in
news:q47ngep5tumk872r2a5i8f1jmc64s3hjhf@4ax.com:

On Thu, 20 Jun 2019 14:38:25 +0000 (UTC),
DecadentLinuxUserNumeroUno@decadence.org wrote:

John Larkin <jjlarkin@highlandtechnology.com> wrote in
news:s92ngepq1qupotbukg6toj0hjrqt1u0d2u@4ax.com:

On Wed, 19 Jun 2019 22:13:18 -0700 (PDT), jurb6006@gmail.com
wrote:

Bottom posting. (Google here)

No insulator. Could glue a chip to it and have some advantages
with that. Power transistor cases, much better than plastic and
if you can get the silicon to stick to it you have a really good
package.

In my opinion, ceramic is a bit too hard to machine for use as
heat sinks per se. This stuff about near has to be molded to its
shape the first time. With holes.

I sure hope that the semi contact area is ground flat. Moulded
ceramic is usually rough, and roughness wrecks thermal
conductivity. But I guess that's not so important for a small
heat sink.



The flatness is what counts. Coplanarity is what is important
when mating the heat source to the sink.

No, surface texture at that level has ZERO effect for or against
heat flow. The interface is where most is lost, and that is about
the interface medium. Air = no good. So we put fillers in.
sil-pad tabs or liquid 'paste'.
The surface quality of molded ceramic is fine grained, and
presents exactly ZERO difference.

If it were actually 'rough' you would have a valid point. But
the
profile of the texture of a molded ceramic face is far too fine to
have any effect against thermal flow.

IF it was ground with 36 grit. MAYBE. But the surface quality
of
ceramic has zero effect. Far more important is a tight, flat
interface. Whereas the 36 grit ROUGH surface WOULD impede thermal
flow. But not really a lot. You said it "wrecks it" but it
doesn't really. Non-coplanarity does.

You could find out with your IR imager. The difference is
practically nil until the roughbess gets pretty far up there.

We had a guy who insisted on soldering the big FETs down before
mounting the heat sink. If they were individual sinks sure, but a
gang of 12 FETs across the edge of a board there to mate with a
heat sink poses problems with his method. We were frying FETs
within seconds of use. I showed him that we needed to mount the
heat sink and FET packages onto the PCB and THEN solder the FET
legs.

Both roughness and flatness matter for good heat conduction.

Yes, but what you fail to note is the actual degree of
roughness. I used to polish stainless steel plates so I know what
surface quality is. I also know about the interface mediums used
between heat sources and heat sinks.

Flatness matters, but once one is below a certain degree of
surface smoothness, there is no difference in conduction.

Thermal grease is not actually a very good heat conductor, and it
needs to be thin to minimize theta.

Yes, but it comes down to mils, not microinches. The 'matte'
finish on a perfectly flat A1N insulator has been perfectly fine for
decades.

If the contacting surfaces
aren't flat and smooth, that hurts. We machine aluminum extrusions
flat for high power stuff,

Oh boy!

because they tend to be wiggly
as-extruded.

Yes. Most credible companies mill mating surfaces for the heat
source to mate to the heat sink.

Our ceramic AlN insulators are lapped to basically
optical limits.

By you guys or the maker? I'd bet immeasurable difference between
an off the shelf A1N insulator and an "optically lapped" version.
It is serious overkill with a nil net gain result.

>Transistor packages tend to be very good.

Not really. A copper slab plated. That 'slab media' is extruded
and shear cut when they are building those FETs and transistors.
It is very flat, but not in any way an "optical quality lapped
surface". You have taken your obsession a bit too far and no longer
have a picture of what is happening.

Thermal silicone grease has ceramic filler particles,

SOME thermal grease has ceramic filler particles. Some have
Silver. Some have other media. Some have NO granular media at all.

which may
help conduction but increases gap. They compress to below 100
microinches, which is good. I tried some diamond filled grease,
but the particles were so big that they increased the gap, with no
net benefit.

As long as electrical conduction is not an issue, a silver filled
thermal paste or epoxy is best.

Why do I say this? Because THAT is what the entire microchip
industry uses for their die attachment.

Their stuff is NOT polished to a mirror finish either.

There is a point at which any 'returns' or gains are minimal or
even immeasurable. You are worrying about a molded ceramic
insulator surface quality that is far and well below the profile
level which causes a conduction differential.

You have problems looking at the bigger picture stuff, and
apparently at the micro scale as well.

Zero gap is zero gap. Flat, co-planar mating is what is required
MOST. A mirror finished surface intrfaces no better than a surface
with a 15 micron pebble matte finish. You are well below the point
where it matters or even shows a difference.

Also, not that the tabs have a hole that is offset from the
conduction surface. That means that the clamping force on it causes
it to want to tip a bit away from co-planar mating. There are a lot
of mounting clamps out there now, which clamp against the main body
of the part. That too is important.

 

John Larkin <jjlarkin@highlandtechnology.com> wrote in
news:quangepho93g085qhetg2k70ud8fk4clij@4ax.com:

Silver epoxy is used for its electrical conductivity.

Silver conducts heat better than copper does. Silver filled epoxy is
for conduction of BOTH heat and electrons.

On CPUs at Intel, it is used specifically for its thermal conduction
qualities.

 

[John Larkin]

On Thu, 20 Jun 2019 15:35:18 +0000 (UTC),
DecadentLinuxUserNumeroUno@decadence.org wrote:

As long as electrical conduction is not an issue, a silver filled
thermal paste or epoxy is best.

Why do I say this? Because THAT is what the entire microchip
industry uses for their die attachment.

Silver epoxy is used for its electrical conductivity.

Their stuff is NOT polished to a mirror finish either.

There is a point at which any 'returns' or gains are minimal or
even immeasurable. You are worrying about a molded ceramic
insulator surface quality that is far and well below the profile
level which causes a conduction differential.

You have problems looking at the bigger picture stuff, and
apparently at the micro scale as well.

One thing I do is measure thermal conductivity and then do what works.

https://www.dropbox.com/s/0pr4hq6euhjn4yr/DSC02169.JPG?raw=1

https://www.dropbox.com/s/9vt61si6taj2ivw/DSC02177.JPG?raw=1

That cuts through a lot of theorizing. And creative data sheets.

Zero gap is zero gap. Flat, co-planar mating is what is required
MOST. A mirror finished surface intrfaces no better than a surface
with a 15 micron pebble matte finish. You are well below the point
where it matters or even shows a difference.

Also, not that the tabs have a hole that is offset from the
conduction surface. That means that the clamping force on it causes
it to want to tip a bit away from co-planar mating. There are a lot
of mounting clamps out there now, which clamp against the main body
of the part. That too is important.

This uses clamp mounting of the power fets onto a very flat copper
heat spreader, with no insulators.

https://www.dropbox.com/s/nmyb9pz0qpma2xa/Amp.jpg?dl=0

The entire heat sink is the amplifier output node, insulated from the
chassis. 17 kilowatts peak power for NMR gradient drive.




--

John Larkin Highland Technology, Inc

lunatic fringe electronics

 

[John Larkin]

On Thu, 20 Jun 2019 16:33:46 +0000 (UTC),
DecadentLinuxUserNumeroUno@decadence.org wrote:

John Larkin <jjlarkin@highlandtechnology.com> wrote in
news:quangepho93g085qhetg2k70ud8fk4clij@4ax.com:

That cuts through a lot of theorizing. And creative data sheets.


You thinking that a matte finish ceramic is going to conduct better
with a mirrored surface is ludicrous.

The flatter, the better, whatever scale you measure it on.


--

John Larkin Highland Technology, Inc

lunatic fringe electronics

 

John Larkin <jjlarkin@highlandtechnology.com> wrote in
news:quangepho93g085qhetg2k70ud8fk4clij@4ax.com:

This uses clamp mounting of the power fets onto a very flat copper
heat spreader, with no insulators.

https://www.dropbox.com/s/nmyb9pz0qpma2xa/Amp.jpg?dl=0

We used those too. They rely on the spring characteristics of the
clamp material. I think they could have made them slightly thicker,
and produce about 15 or 20 lbs more force aginst the tab.

Nice design where the plate offset matches the leg heights. Easy to
build and then solder.

Ours was perpendicular to the PCB and was only 2kW but that was
continuous. We ended up using a sink with no fins. It was a
rectangular tube and allowed better air management and worked fine for
the task.

 

[Rick C]

On Thursday, June 20, 2019 at 12:38:22 PM UTC-4, John Larkin wrote:

On Thu, 20 Jun 2019 16:33:46 +0000 (UTC),
DecadentLinuxUserNumeroUno@decadence.org wrote:

John Larkin <jjlarkin@highlandtechnology.com> wrote in
news:quangepho93g085qhetg2k70ud8fk4clij@4ax.com:

That cuts through a lot of theorizing. And creative data sheets.


You thinking that a matte finish ceramic is going to conduct better
with a mirrored surface is ludicrous.

The flatter, the better, whatever scale you measure it on.

Within the law of diminishing returns. "Better" is not always better.

--

Rick C.

---- Get 1,000 miles of free Supercharging
---- Tesla referral code - https://ts.la/richard11209

 

John Larkin <jjlarkin@highlandtechnology.com> wrote in
news:quangepho93g085qhetg2k70ud8fk4clij@4ax.com:

That cuts through a lot of theorizing. And creative data sheets.

You thinking that a matte finish ceramic is going to conduct better
with a mirrored surface is ludicrous.

Maybe if it was pebbled like a hip joint replacement, but at the
surface texture it has... not one single bit of difference.

 

John Larkin <jjlarkin@highlandtechnology.com> wrote in
news:vfdngep4a2p998telh179npgpqvo7pk0oe@4ax.com:

On Thu, 20 Jun 2019 16:33:46 +0000 (UTC),
DecadentLinuxUserNumeroUno@decadence.org wrote:

John Larkin <jjlarkin@highlandtechnology.com> wrote in
news:quangepho93g085qhetg2k70ud8fk4clij@4ax.com:

That cuts through a lot of theorizing. And creative data sheets.


You thinking that a matte finish ceramic is going to conduct
better
with a mirrored surface is ludicrous.

The flatter, the better, whatever scale you measure it on.

You are incorrect. *I* said flatness is important. YOU ranted on
about the surface condition.

Flat is better. Polished? Does not matter.

The flatness matters. The roughness will only matter AFTER it
rises above a certain level on the profilometer.

You jacking off at the mouth about a flat face with a matte finish
comprised of 15 micron surface undulations causing less cooling
efficiency is a joke. Period.

The flatness is ALL that matters once the surface quality is past
a certain point. That point is way up in the "36 grit" scratch
profile range, not anywhere near the surface profile of a matte
finish ceramic face with 15 micron bumps.

 

Rick C <gnuarm.deletethisbit@gmail.com> wrote in
news:97cd6668-ead2-454e-93d1-88d61ada71b4@googlegroups.com:

On Thursday, June 20, 2019 at 12:38:22 PM UTC-4, John Larkin
wrote:
On Thu, 20 Jun 2019 16:33:46 +0000 (UTC),
DecadentLinuxUserNumeroUno@decadence.org wrote:

John Larkin <jjlarkin@highlandtechnology.com> wrote in
news:quangepho93g085qhetg2k70ud8fk4clij@4ax.com:

That cuts through a lot of theorizing. And creative data
sheets.


You thinking that a matte finish ceramic is going to conduct
better
with a mirrored surface is ludicrous.

The flatter, the better, whatever scale you measure it on.

Within the law of diminishing returns. "Better" is not always
better.

He is experiencing science observer overkill.

I know for a fact that the difference is so small as to not even
be measurable. The term nil works here.

One can take ten of the FETs and do a 'thumbprint' job with them
on a known flat surface (an inspection block), and you will find
that even they are not all as flat as you might like to think they
are. We even "honed" some to prove it. Aside from the copper
oxidation problem with the now exposed bare copper, they actually
conduct heat away better. But the difference is so slight as to not
matter at all.

 

On Mon, 17 Jun 2019 23:38:43 -0700, boB <boB@K7IQ.com> wrote:

On Tue, 18 Jun 2019 04:42:39 GMT, Jan Panteltje
pNaOnStPeAlMtje@yahoo.com> wrote:

On a sunny day (Mon, 17 Jun 2019 21:02:38 -0700) it happened John Larkin
jjlarkin@highlandtechnology.com> wrote in
uhoggehbfa6gbmevhg9u00d5duvicqdarv@4ax.com>:

On Tue, 18 Jun 2019 03:41:57 GMT, Jan Panteltje
pNaOnStPeAlMtje@yahoo.com> wrote:

On a sunny day (Mon, 17 Jun 2019 19:29:35 -0400) it happened Phil Hobbs
pcdhSpamMeSenseless@electrooptical.net> wrote in
9sWdnapK4K78v5XAnZ2dnUU7-d3NnZ2d@supernews.com>:

On 6/17/19 11:18 AM, Tim Williams wrote:
https://www.digikey.com/product-detail/en/ohmite/CA-TX1-050-E/CA-TX1-050-E-ND/9954358


Damn, didn't realize they were making full heatsinks out of ceramic now.
Doesn't seem to be AlN either, just boring old Al2O3.

Performance looks comparable, despite the relatively low Rth of the
material (compared to AlN and Al).  Not spendy either.

Tim


Eight bucks for a 1x2 inch heatsink "isn't spendy"? Aluminum ones run
maybe 80 cents in onesies on Digikey.

Cheers

Phil Hobbs

Dunno. mostly profit.
a quick search for ceramic heatsink on ebay
finds many for Raspberry 3B+ at 99 cents.
OK, smaller, no pins, but material cost?
https://www.ebay.com/itm/333190430314

Could have some advantages.

Probably thermally useless.

I do not think so, that particular raspi had a big thermal problem
later fixed IIRC.
Those thing must really work?

What's the thermal resistance of this kind of stuff ?

Ceramic resistors come to mind. If it really works OK but not as
good as aluminum, then it might have an advantage like Win says
about the capacitance and could help common mode noise issues that
happen with aluminum heat sinks.

Does the thermal resistance of a power resistor coating matter all
that much (within reason)? At least for a resistor that isn't
intended to be connected to a heat sink. Power resistors run at much
higher temperatures than the normal semiconductor parts and the area
of the case is larger than the element. Thermal conductivity helps
moving heat. It doesn't help dissipate it.

Can't make aluminim castings out of the stuff. Or can you ?

 

[John Larkin]

On Fri, 21 Jun 2019 12:35:26 -0400, krw@notreal.com wrote:

On Mon, 17 Jun 2019 23:38:43 -0700, boB <boB@K7IQ.com> wrote:

On Tue, 18 Jun 2019 04:42:39 GMT, Jan Panteltje
pNaOnStPeAlMtje@yahoo.com> wrote:

On a sunny day (Mon, 17 Jun 2019 21:02:38 -0700) it happened John Larkin
jjlarkin@highlandtechnology.com> wrote in
uhoggehbfa6gbmevhg9u00d5duvicqdarv@4ax.com>:

On Tue, 18 Jun 2019 03:41:57 GMT, Jan Panteltje
pNaOnStPeAlMtje@yahoo.com> wrote:

On a sunny day (Mon, 17 Jun 2019 19:29:35 -0400) it happened Phil Hobbs
pcdhSpamMeSenseless@electrooptical.net> wrote in
9sWdnapK4K78v5XAnZ2dnUU7-d3NnZ2d@supernews.com>:

On 6/17/19 11:18 AM, Tim Williams wrote:
https://www.digikey.com/product-detail/en/ohmite/CA-TX1-050-E/CA-TX1-050-E-ND/9954358


Damn, didn't realize they were making full heatsinks out of ceramic now.
Doesn't seem to be AlN either, just boring old Al2O3.

Performance looks comparable, despite the relatively low Rth of the
material (compared to AlN and Al).  Not spendy either.

Tim


Eight bucks for a 1x2 inch heatsink "isn't spendy"? Aluminum ones run
maybe 80 cents in onesies on Digikey.

Cheers

Phil Hobbs

Dunno. mostly profit.
a quick search for ceramic heatsink on ebay
finds many for Raspberry 3B+ at 99 cents.
OK, smaller, no pins, but material cost?
https://www.ebay.com/itm/333190430314

Could have some advantages.

Probably thermally useless.

I do not think so, that particular raspi had a big thermal problem
later fixed IIRC.
Those thing must really work?

What's the thermal resistance of this kind of stuff ?

Ceramic resistors come to mind. If it really works OK but not as
good as aluminum, then it might have an advantage like Win says
about the capacitance and could help common mode noise issues that
happen with aluminum heat sinks.

Does the thermal resistance of a power resistor coating matter all
that much (within reason)? At least for a resistor that isn't
intended to be connected to a heat sink. Power resistors run at much
higher temperatures than the normal semiconductor parts and the area
of the case is larger than the element. Thermal conductivity helps
moving heat. It doesn't help dissipate it.

Can't make aluminim castings out of the stuff. Or can you ?

The ceramic allows the resistor to run really hot. But I have melted
that too.


--

John Larkin Highland Technology, Inc

lunatic fringe electronics

 

[Tim Williams]

<krw@notreal.com> wrote in message
news:ub1qgetodft4e52nf6o1n1sq3fi59cs7pq@4ax.com...

Does the thermal resistance of a power resistor coating matter all
that much (within reason)? At least for a resistor that isn't
intended to be connected to a heat sink. Power resistors run at much
higher temperatures than the normal semiconductor parts and the area
of the case is larger than the element. Thermal conductivity helps
moving heat. It doesn't help dissipate it.

Other than pulse ratings, no, conductivity of the cement doesn't matter
much, considering the pitiful conductivity of the air surrounding it.

Tim

--
Seven Transistor Labs, LLC
Electrical Engineering Consultation and Design
Website: https://www.seventransistorlabs.com/

 

On Fri, 21 Jun 2019 09:45:07 -0700, John Larkin
<jjlarkin@highlandtechnology.com> wrote:

On Fri, 21 Jun 2019 12:35:26 -0400, krw@notreal.com wrote:

On Mon, 17 Jun 2019 23:38:43 -0700, boB <boB@K7IQ.com> wrote:

On Tue, 18 Jun 2019 04:42:39 GMT, Jan Panteltje
pNaOnStPeAlMtje@yahoo.com> wrote:

On a sunny day (Mon, 17 Jun 2019 21:02:38 -0700) it happened John Larkin
jjlarkin@highlandtechnology.com> wrote in
uhoggehbfa6gbmevhg9u00d5duvicqdarv@4ax.com>:

On Tue, 18 Jun 2019 03:41:57 GMT, Jan Panteltje
pNaOnStPeAlMtje@yahoo.com> wrote:

On a sunny day (Mon, 17 Jun 2019 19:29:35 -0400) it happened Phil Hobbs
pcdhSpamMeSenseless@electrooptical.net> wrote in
9sWdnapK4K78v5XAnZ2dnUU7-d3NnZ2d@supernews.com>:

On 6/17/19 11:18 AM, Tim Williams wrote:
https://www.digikey.com/product-detail/en/ohmite/CA-TX1-050-E/CA-TX1-050-E-ND/9954358


Damn, didn't realize they were making full heatsinks out of ceramic now.
Doesn't seem to be AlN either, just boring old Al2O3.

Performance looks comparable, despite the relatively low Rth of the
material (compared to AlN and Al).  Not spendy either.

Tim


Eight bucks for a 1x2 inch heatsink "isn't spendy"? Aluminum ones run
maybe 80 cents in onesies on Digikey.

Cheers

Phil Hobbs

Dunno. mostly profit.
a quick search for ceramic heatsink on ebay
finds many for Raspberry 3B+ at 99 cents.
OK, smaller, no pins, but material cost?
https://www.ebay.com/itm/333190430314

Could have some advantages.

Probably thermally useless.

I do not think so, that particular raspi had a big thermal problem
later fixed IIRC.
Those thing must really work?

What's the thermal resistance of this kind of stuff ?

Ceramic resistors come to mind. If it really works OK but not as
good as aluminum, then it might have an advantage like Win says
about the capacitance and could help common mode noise issues that
happen with aluminum heat sinks.

Does the thermal resistance of a power resistor coating matter all
that much (within reason)? At least for a resistor that isn't
intended to be connected to a heat sink. Power resistors run at much
higher temperatures than the normal semiconductor parts and the area
of the case is larger than the element. Thermal conductivity helps
moving heat. It doesn't help dissipate it.

Can't make aluminim castings out of the stuff. Or can you ?

The ceramic allows the resistor to run really hot. But I have melted
that too.

Right but it doesn't need to have an especially low thermal
resistance.

 

On Fri, 21 Jun 2019 12:21:01 -0500, "Tim Williams"
<tiwill@seventransistorlabs.com> wrote:

krw@notreal.com> wrote in message
news:ub1qgetodft4e52nf6o1n1sq3fi59cs7pq@4ax.com...
Does the thermal resistance of a power resistor coating matter all
that much (within reason)? At least for a resistor that isn't
intended to be connected to a heat sink. Power resistors run at much
higher temperatures than the normal semiconductor parts and the area
of the case is larger than the element. Thermal conductivity helps
moving heat. It doesn't help dissipate it.

Other than pulse ratings, no, conductivity of the cement doesn't matter
much, considering the pitiful conductivity of the air surrounding it.

Right, so why would one think that material is great for heatsinking
semiconductor devices?