Heatsink, just don't drop it on concrete

[Joerg]

On 2019-06-17 18:40, Winfield Hill wrote:

Joerg wrote...

On 2019-06-17 16:29, Phil Hobbs wrote:
On 6/17/19 11:18 AM, Tim Williams wrote:

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

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

But it does have its bling factor. Just imagine the
unfettered flow of electrons in a class D stage,
using space-age ceramic technology for the ultimate
sound experience

I struggle with the high heatsink capacitance of power
transistor tabs. $7 is cheap at the price for s solution.
Wanna make a 500V/us fast-slewing HV amplifier stage?
Find a low-C power part, and a low-C heatsink.
Read all about it in the soon-to-be-out AoE x-Chapters.

That almost cries for oil cooling. Of course, when I did that with a
larger setup the container began to weep. I must have botched one of the
solder seams.

--
Regards, Joerg

http://www.analogconsultants.com/

 

[John Larkin]

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.

The virtue of making resistors out of ceramic is that they can run
really hot.

AlN surface-mount resistors are good because they can conduct a lot of
heat into PCB copper pours, or into aluminum heat sinks.

Either way, you need heat spreading and surface area to cool things.

One thing I like is punched copper disks, like jewelry makers use.
Cheap on Amazon or Ebay. Epoxy one to a part and it spreads the heat
laterally and increases surface area. Any air flow sweeps the top and
the bottom.


--

John Larkin Highland Technology, Inc

lunatic fringe electronics

 

[legg]

On Mon, 17 Jun 2019 19:29:35 -0400, Phil Hobbs
<pcdhSpamMeSenseless@electrooptical.net> wrote:

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

Getting low capacitive conduction and radiation from something
heatsunk to a conductive surface is both clumsy and expensive.


I wonder where the target market is? Curious mixture of old school
thinking and . . . In a low labor price market, it will be a hard
sell.

Why are simple AlO2 wafers still so $$$ ? Even sourced off-shore?

RL

 

[John Larkin]

On 18 Jun 2019 03:05:33 -0700, Winfield Hill <winfieldhill@yahoo.com>
wrote:

John Larkin wrote...

Winfield Hill wrote:
Joerg wrote...
Phil Hobbs wrote:
Tim Williams wrote:

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

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

But it does have its bling factor. Just imagine the
unfettered flow of electrons in a class D stage,
using space-age ceramic technology for the ultimate
sound experience

I struggle with the high heatsink capacitance of power
transistor tabs. $7 is cheap at the price for s solution.
Wanna make a 500V/us fast-slewing HV amplifier stage?
Find a low-C power part, and a low-C heatsink.
Read all about it in the soon-to-be-out AoE x-Chapters.

An AlN insulator over a water-cooled aluminum or copper
block is pretty good for cooling vs capacitance. Flowing
water directly onto the fet tab would be a lot better.

Yep, I'd have much less struggle with my thermal
problems, if my whole circuit was in an oil bath.

Oil is nasty. If you get water on your jeans, it evaporates.

I was thinking about a cavity and some water channels machined in an
aluminum block. The Cree would push into a cavity with an o-ring seal.
Water would flow on the bottom of the fet. Cooling would be awesome
and capacitance minimal.

My average drain voltage is low (I'm making narrow positive pulses) so
electrolysis might be managable. One could bond a very thin AlN slab
to the fet tab too.




--

John Larkin Highland Technology, Inc

lunatic fringe electronics

 

[John Larkin]

On Tue, 18 Jun 2019 11:17:00 -0400, legg <legg@nospam.magma.ca> wrote:

On Mon, 17 Jun 2019 19:29:35 -0400, Phil Hobbs
pcdhSpamMeSenseless@electrooptical.net> wrote:

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

Getting low capacitive conduction and radiation from something
heatsunk to a conductive surface is both clumsy and expensive.

And necessary to make fast amps and pulse generators. Radiation
doesn't do much to cool a small part, and fast circuits need small
parts.

I wonder where the target market is? Curious mixture of old school
thinking and . . . In a low labor price market, it will be a hard
sell.

Making a small, 7 ns, 1KV, 4 MHz pulse generator is hardly old-school.
It is a serious thermal-capacitive challenge.

http://www.highlandtechnology.com/DSS/T870DS.shtml

That one was *hard*, electrically and especially thermally.

Why are simple AlO2 wafers still so $$$ ? Even sourced off-shore?

They are cheap, but alumina conducts at about 25 w/mK. Alumium nitride
is maybe 5x better, close to common aluminum alloys.

The only reasonably affordable better insulator is BeO, and beryllium
is toxic.


--

John Larkin Highland Technology, Inc

lunatic fringe electronics

 

[legg]

On Tue, 18 Jun 2019 08:44:55 -0700, John Larkin
<jjlarkin@highlandtechnology.com> wrote:

On Tue, 18 Jun 2019 11:17:00 -0400, legg <legg@nospam.magma.ca> wrote:

On Mon, 17 Jun 2019 19:29:35 -0400, Phil Hobbs
pcdhSpamMeSenseless@electrooptical.net> wrote:

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

Getting low capacitive conduction and radiation from something
heatsunk to a conductive surface is both clumsy and expensive.

And necessary to make fast amps and pulse generators. Radiation
doesn't do much to cool a small part, and fast circuits need small
parts.



I wonder where the target market is? Curious mixture of old school
thinking and . . . In a low labor price market, it will be a hard
sell.

Making a small, 7 ns, 1KV, 4 MHz pulse generator is hardly old-school.
It is a serious thermal-capacitive challenge.

http://www.highlandtechnology.com/DSS/T870DS.shtml

That one was *hard*, electrically and especially thermally.


Why are simple AlO2 wafers still so $$$ ? Even sourced off-shore?

They are cheap, but alumina conducts at about 25 w/mK. Alumium nitride
is maybe 5x better, close to common aluminum alloys.

The only reasonably affordable better insulator is BeO, and beryllium
is toxic.

Philips used to offer a ~2in x 4in Alox plate laser-cut to accept a
to220 spring clip. It mounted to printed wiring using folded tinned
metal grips on the edges. MOQ ~ 1 gazillion.

RL

 

[Clifford Heath]

On 19/6/19 12:10 am, John Larkin wrote:

Either way, you need heat spreading and surface area to cool things.

One thing I like is punched copper disks, like jewelry makers use.
Cheap on Amazon or Ebay. Epoxy one to a part and it spreads the heat
laterally and increases surface area. Any air flow sweeps the top and
the bottom.

Epoxy is not great with heat though. What product do you use?

Clifford Heath

 

[John Larkin]

On Wed, 19 Jun 2019 08:28:17 +1000, Clifford Heath
<no.spam@please.net> wrote:

On 19/6/19 12:10 am, John Larkin wrote:
Either way, you need heat spreading and surface area to cool things.

One thing I like is punched copper disks, like jewelry makers use.
Cheap on Amazon or Ebay. Epoxy one to a part and it spreads the heat
laterally and increases surface area. Any air flow sweeps the top and
the bottom.

Epoxy is not great with heat though. What product do you use?

Clifford Heath

Some thermally conductive stuff,

AAVID 4952G

The thermal conductivity is only mediocre, 1.4 w/mK. The trick is to
keep it thin.


--

John Larkin Highland Technology, Inc
picosecond timing precision measurement

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

 

Joerg <news@analogconsultants.com> wrote in
news:gms9npFeqjaU1@mid.individual.net:

On 2019-06-17 18:40, Winfield Hill wrote:
Joerg wrote...

On 2019-06-17 16:29, Phil Hobbs wrote:
On 6/17/19 11:18 AM, Tim Williams wrote:

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

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

But it does have its bling factor. Just imagine the
unfettered flow of electrons in a class D stage,
using space-age ceramic technology for the ultimate
sound experience

I struggle with the high heatsink capacitance of power
transistor tabs. $7 is cheap at the price for s solution.
Wanna make a 500V/us fast-slewing HV amplifier stage?
Find a low-C power part, and a low-C heatsink.
Read all about it in the soon-to-be-out AoE x-Chapters.


That almost cries for oil cooling. Of course, when I did that with
a larger setup the container began to weep. I must have botched
one of the solder seams.

Fluorinert is dielectric and a lot less messy. (and a lot more
expensive) Not better than water thermally, but far better than
water around electrical circuits!

 

[John Larkin]

On Wed, 19 Jun 2019 09:54:50 -0400, Phil Hobbs
<pcdhSpamMeSenseless@electrooptical.net> wrote:

On 6/17/19 11:16 PM, Tim Williams wrote:
"Winfield Hill" <winfieldhill@yahoo.com> wrote in message
news:qe9fee01pod@drn.newsguy.com...
I struggle with the high heatsink capacitance of power
transistor tabs. $7 is cheap at the price for s solution.
Wanna make a 500V/us fast-slewing HV amplifier stage?
Find a low-C power part, and a low-C heatsink. 
Read all about it in the soon-to-be-out AoE x-Chapters.


Y'know, I'll bet it's transparent to long IR as well.  Not that there's
much to see on the metal backside of a transistor or what have you, but
it may be useful sometimes.  A sil-pad would definitely be emissive,
grease may be as well.

Tim

Nah, sapphire becomes opaque around 5 um, and polycrystalline alumina
will be worse.

Cheers

Phil Hobbs

We sometimes want to thermal image a board in a box. If we remove the
top cover, the air flow all changes. FLIR sells a
thermally-transparent (looks like glass) window for some kilobucks
that we could install in the cover, or use to replace the cover.

We use the black plastic from the cheapest, thinnest garbage bags.


--

John Larkin Highland Technology, Inc

lunatic fringe electronics

 

[John Larkin]

On Tue, 18 Jun 2019 07:11:25 -0700, Joerg <news@analogconsultants.com>
wrote:

On 2019-06-17 18:40, Winfield Hill wrote:
Joerg wrote...

On 2019-06-17 16:29, Phil Hobbs wrote:
On 6/17/19 11:18 AM, Tim Williams wrote:

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

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

But it does have its bling factor. Just imagine the
unfettered flow of electrons in a class D stage,
using space-age ceramic technology for the ultimate
sound experience

I struggle with the high heatsink capacitance of power
transistor tabs. $7 is cheap at the price for s solution.
Wanna make a 500V/us fast-slewing HV amplifier stage?
Find a low-C power part, and a low-C heatsink.
Read all about it in the soon-to-be-out AoE x-Chapters.


That almost cries for oil cooling. Of course, when I did that with a
larger setup the container began to weep. I must have botched one of the
solder seams.

Every once in a whie one of my people will suggest oil cooling or
potting. A few hours alone locked in a dark closet seems to help them.


--

John Larkin Highland Technology, Inc

lunatic fringe electronics

 

[Phil Hobbs]

On 6/17/19 11:16 PM, Tim Williams wrote:

"Winfield Hill" <winfieldhill@yahoo.com> wrote in message
news:qe9fee01pod@drn.newsguy.com...
I struggle with the high heatsink capacitance of power
transistor tabs. $7 is cheap at the price for s solution.
Wanna make a 500V/us fast-slewing HV amplifier stage?
Find a low-C power part, and a low-C heatsink. 
Read all about it in the soon-to-be-out AoE x-Chapters.


Y'know, I'll bet it's transparent to long IR as well.  Not that there's
much to see on the metal backside of a transistor or what have you, but
it may be useful sometimes.  A sil-pad would definitely be emissive,
grease may be as well.

Tim

Nah, sapphire becomes opaque around 5 um, and polycrystalline alumina
will be worse.

Cheers

Phil Hobbs

--
Dr Philip C D Hobbs
Principal Consultant
ElectroOptical Innovations LLC / Hobbs ElectroOptics
Optics, Electro-optics, Photonics, Analog Electronics
Briarcliff Manor NY 10510

http://electrooptical.net
http://hobbs-eo.com

 

[Joerg]

On 2019-06-19 07:15, John Larkin wrote:

On Tue, 18 Jun 2019 07:11:25 -0700, Joerg <news@analogconsultants.com
wrote:

On 2019-06-17 18:40, Winfield Hill wrote:
Joerg wrote...

On 2019-06-17 16:29, Phil Hobbs wrote:
On 6/17/19 11:18 AM, Tim Williams wrote:

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

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

But it does have its bling factor. Just imagine the
unfettered flow of electrons in a class D stage,
using space-age ceramic technology for the ultimate
sound experience

I struggle with the high heatsink capacitance of power
transistor tabs. $7 is cheap at the price for s solution.
Wanna make a 500V/us fast-slewing HV amplifier stage?
Find a low-C power part, and a low-C heatsink.
Read all about it in the soon-to-be-out AoE x-Chapters.


That almost cries for oil cooling. Of course, when I did that with a
larger setup the container began to weep. I must have botched one of the
solder seams.

Every once in a whie one of my people will suggest oil cooling or
potting. A few hours alone locked in a dark closet seems to help them.

I have used oil cooling over decades. It works. You just have to make
sure there is no mess. At least when married.

--
Regards, Joerg

http://www.analogconsultants.com/

 

[Rodney Pont]

On Wed, 19 Jun 2019 07:27:56 -0700, John Larkin wrote:

We sometimes want to thermal image a board in a box. If we remove the
top cover, the air flow all changes. FLIR sells a
thermally-transparent (looks like glass) window for some kilobucks
that we could install in the cover, or use to replace the cover.

We use the black plastic from the cheapest, thinnest garbage bags.

Wouldn't clingfilm work?

--
Regards - Rodney Pont
The from address exists but is mostly dumped,
please send any emails to the address below
e-mail rpont (at) gmail (dot) com

 

[John Larkin]

On Wed, 19 Jun 2019 17:50:11 +0100 (BST), "Rodney Pont"
<mlist4@infohit.me.uk> wrote:

On Wed, 19 Jun 2019 07:27:56 -0700, John Larkin wrote:

We sometimes want to thermal image a board in a box. If we remove the
top cover, the air flow all changes. FLIR sells a
thermally-transparent (looks like glass) window for some kilobucks
that we could install in the cover, or use to replace the cover.

We use the black plastic from the cheapest, thinnest garbage bags.

Wouldn't clingfilm work?

Some of it does. Again, the cheapest stuff is the thinnest.


--

John Larkin Highland Technology, Inc
picosecond timing precision measurement

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

 

[Joerg]

On 2019-06-18 07:45, John Larkin wrote:

On 18 Jun 2019 03:05:33 -0700, Winfield Hill <winfieldhill@yahoo.com
wrote:

John Larkin wrote...

Winfield Hill wrote:
Joerg wrote...
Phil Hobbs wrote:
Tim Williams wrote:

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

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

But it does have its bling factor. Just imagine the
unfettered flow of electrons in a class D stage,
using space-age ceramic technology for the ultimate
sound experience

I struggle with the high heatsink capacitance of power
transistor tabs. $7 is cheap at the price for s solution.
Wanna make a 500V/us fast-slewing HV amplifier stage?
Find a low-C power part, and a low-C heatsink.
Read all about it in the soon-to-be-out AoE x-Chapters.

An AlN insulator over a water-cooled aluminum or copper
block is pretty good for cooling vs capacitance. Flowing
water directly onto the fet tab would be a lot better.

Yep, I'd have much less struggle with my thermal
problems, if my whole circuit was in an oil bath.

Oil is nasty. If you get water on your jeans, it evaporates.

Not a problem if people dress accordingly

https://www.tokyohive.com/upload/2011/02/00delete11143.jpg

I was thinking about a cavity and some water channels machined in an
aluminum block. The Cree would push into a cavity with an o-ring seal.
Water would flow on the bottom of the fet. Cooling would be awesome
and capacitance minimal.

My average drain voltage is low (I'm making narrow positive pulses) so
electrolysis might be managable. One could bond a very thin AlN slab
to the fet tab too.

Really hoppy India Pale Ale might also work.

--
Regards, Joerg

http://www.analogconsultants.com/

 

[whit3rd]

On Tuesday, June 18, 2019 at 7:45:38 AM UTC-7, John Larkin wrote:

> Oil is nasty. If you get water on your jeans, it evaporates.

The compatible garments are wool; oil just diffuses in, doesn't
leave a spot. Wool shirt is great for machine shop (but roll up the
sleeves before using power tools, of course).

 

[Phil Hobbs]

On 6/19/19 10:27 AM, John Larkin wrote:

On Wed, 19 Jun 2019 09:54:50 -0400, Phil Hobbs
pcdhSpamMeSenseless@electrooptical.net> wrote:

On 6/17/19 11:16 PM, Tim Williams wrote:
"Winfield Hill" <winfieldhill@yahoo.com> wrote in message
news:qe9fee01pod@drn.newsguy.com...
I struggle with the high heatsink capacitance of power
transistor tabs. $7 is cheap at the price for s solution.
Wanna make a 500V/us fast-slewing HV amplifier stage?
Find a low-C power part, and a low-C heatsink. 
Read all about it in the soon-to-be-out AoE x-Chapters.


Y'know, I'll bet it's transparent to long IR as well.  Not that there's
much to see on the metal backside of a transistor or what have you, but
it may be useful sometimes.  A sil-pad would definitely be emissive,
grease may be as well.

Tim

Nah, sapphire becomes opaque around 5 um, and polycrystalline alumina
will be worse.

Cheers

Phil Hobbs

We sometimes want to thermal image a board in a box. If we remove the
top cover, the air flow all changes. FLIR sells a
thermally-transparent (looks like glass) window for some kilobucks
that we could install in the cover, or use to replace the cover.

We use the black plastic from the cheapest, thinnest garbage bags.

Garbage bags are low-density polyethylene, which works pretty well in
1-mil gauge. I used that in my Footprints sensors to suppress
convection near the sensor film.

HDPE is better if you can get it thin enough.

Cheers

Phil Hobbs



--
Dr Philip C D Hobbs
Principal Consultant
ElectroOptical Innovations LLC / Hobbs ElectroOptics
Optics, Electro-optics, Photonics, Analog Electronics
Briarcliff Manor NY 10510

http://electrooptical.net
http://hobbs-eo.com

 

[Rick C]

On Wednesday, June 19, 2019 at 8:32:42 PM UTC-4, Phil Hobbs wrote:

On 6/19/19 10:27 AM, John Larkin wrote:
On Wed, 19 Jun 2019 09:54:50 -0400, Phil Hobbs
pcdhSpamMeSenseless@electrooptical.net> wrote:

On 6/17/19 11:16 PM, Tim Williams wrote:
"Winfield Hill" <winfieldhill@yahoo.com> wrote in message
news:qe9fee01pod@drn.newsguy.com...
I struggle with the high heatsink capacitance of power
transistor tabs. $7 is cheap at the price for s solution.
Wanna make a 500V/us fast-slewing HV amplifier stage?
Find a low-C power part, and a low-C heatsink. 
Read all about it in the soon-to-be-out AoE x-Chapters.


Y'know, I'll bet it's transparent to long IR as well.  Not that there's
much to see on the metal backside of a transistor or what have you, but
it may be useful sometimes.  A sil-pad would definitely be emissive,
grease may be as well.

Tim

Nah, sapphire becomes opaque around 5 um, and polycrystalline alumina
will be worse.

Cheers

Phil Hobbs

We sometimes want to thermal image a board in a box. If we remove the
top cover, the air flow all changes. FLIR sells a
thermally-transparent (looks like glass) window for some kilobucks
that we could install in the cover, or use to replace the cover.

We use the black plastic from the cheapest, thinnest garbage bags.


Garbage bags are low-density polyethylene, which works pretty well in
1-mil gauge. I used that in my Footprints sensors to suppress
convection near the sensor film.

HDPE is better if you can get it thin enough.

Why, what is better about it? HDPE is milk jugs and kayaks. Both pretty thick. Where do you find it thin?

--

Rick C.

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

 

[Phil Hobbs]

On 6/19/19 10:32 PM, Rick C wrote:

On Wednesday, June 19, 2019 at 8:32:42 PM UTC-4, Phil Hobbs wrote:
On 6/19/19 10:27 AM, John Larkin wrote:
On Wed, 19 Jun 2019 09:54:50 -0400, Phil Hobbs
pcdhSpamMeSenseless@electrooptical.net> wrote:

On 6/17/19 11:16 PM, Tim Williams wrote:
"Winfield Hill" <winfieldhill@yahoo.com> wrote in message
news:qe9fee01pod@drn.newsguy.com...
I struggle with the high heatsink capacitance of power
transistor tabs. $7 is cheap at the price for s solution.
Wanna make a 500V/us fast-slewing HV amplifier stage?
Find a low-C power part, and a low-C heatsink. 
Read all about it in the soon-to-be-out AoE x-Chapters.


Y'know, I'll bet it's transparent to long IR as well.  Not that there's
much to see on the metal backside of a transistor or what have you, but
it may be useful sometimes.  A sil-pad would definitely be emissive,
grease may be as well.

Tim

Nah, sapphire becomes opaque around 5 um, and polycrystalline alumina
will be worse.

Cheers

Phil Hobbs

We sometimes want to thermal image a board in a box. If we remove the
top cover, the air flow all changes. FLIR sells a
thermally-transparent (looks like glass) window for some kilobucks
that we could install in the cover, or use to replace the cover.

We use the black plastic from the cheapest, thinnest garbage bags.


Garbage bags are low-density polyethylene, which works pretty well in
1-mil gauge. I used that in my Footprints sensors to suppress
convection near the sensor film.

HDPE is better if you can get it thin enough.

Why, what is better about it? HDPE is milk jugs and kayaks. Both pretty thick. Where do you find it thin?

You could melt a bleach bottle and smear it out into a thin layer.
Commercially? Dunno.

Cheers

Phil Hobbs


--
Dr Philip C D Hobbs
Principal Consultant
ElectroOptical Innovations LLC / Hobbs ElectroOptics
Optics, Electro-optics, Photonics, Analog Electronics
Briarcliff Manor NY 10510

http://electrooptical.net
http://hobbs-eo.com