Heatsink, just don't drop it on concrete - Page 3

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Re: Heatsink, just don't drop it on concrete
On 2019-06-19 07:15, John Larkin wrote:
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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/

Re: Heatsink, just don't drop it on concrete
On a sunny day (Mon, 17 Jun 2019 16:37:21 -0700) it happened Joerg

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Would be a real brick wall filter :-)


Re: Heatsink, just don't drop it on concrete
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No offense Phil, but I somehow doubt even you can bootstrap the capacitance  
of a heatsink in a sufficiently high frequency switcher. ;-)

Cheap compared to the outright infeasibility of something, or compared to  
more exotic materials (AlN, BeO).

Tim

--  
Seven Transistor Labs, LLC
Electrical Engineering Consultation and Design
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Re: Heatsink, just don't drop it on concrete
On Mon, 17 Jun 2019 21:42:52 -0500, "Tim Williams"

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I'm buying Chinese custom-fabbed AlN insulators, for TO247 SiC fets,
for a dollar or so.

https://www.dropbox.com/s/1991iiogop8mgnk/JRFT_AlN_1.jpg?raw=1

It's TO220 size roughly, but I'm cooling a TO247. Smaller insulator
makes less capacitance.

I really want diamond.


--  

John Larkin         Highland Technology, Inc

lunatic fringe electronics  


Re: Heatsink, just don't drop it on concrete
On a sunny day (Mon, 17 Jun 2019 19:29:35 -0400) it happened Phil Hobbs

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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.

Re: Heatsink, just don't drop it on concrete
On Tue, 18 Jun 2019 03:41:57 GMT, Jan Panteltje

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Probably thermally useless.


--  

John Larkin         Highland Technology, Inc

lunatic fringe electronics  


Re: Heatsink, just don't drop it on concrete
On a sunny day (Mon, 17 Jun 2019 21:02:38 -0700) it happened John Larkin

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

Re: Heatsink, just don't drop it on concrete
On Tue, 18 Jun 2019 04:42:39 GMT, Jan Panteltje

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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.  

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


Re: Heatsink, just don't drop it on concrete
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About 30 W/m.K.  Not great, but comparable to a lot of metals, and still way  
better than air.


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My guess is they're HIPing it with a very carefully shaped die.  I wonder if  
it can be extruded perfectly prismatic, or if the die needs to be shaped in  
such a way that the powder compacts and shrinks as it moves through.

Apparently sapphire can be extruded as well, from a crucible with a  
carefully shaped lid (Czochralski process).  That would be a little too  
fancy for a heatsink, though...

Casting is much less impressive for ceramics.  You make a slip with water,  
suspension agents (deflocculant) and gum.  Pour into a porous mold, the  
water gets sucked out from the surface, then either let it continue or pour  
out the excess to make a hollow form.  Open mold and let dry, then fire.  
The powder has no stiction by itself (unlike clay), which is where the gum  
comes in: a binder is used, that is soluble in water, that doesn't form a  
skin as it dries, and which pyrolyzes to substances that are still sticky,  
without also expanding in the process.  That way, the green ceramic body can  
go straight into the kiln without crumbling to dust.

Pressed shapes are more common I think, other than HIP extruded shapes.  
Ceramic powder and a bit of binder, no water needed.  Make mold 10% or so  
oversized, since it shrinks about that much on firing.

Tim

--  
Seven Transistor Labs, LLC
Electrical Engineering Consultation and Design
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Re: Heatsink, just don't drop it on concrete

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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  


Re: Heatsink, just don't drop it on concrete
On 19/6/19 12:10 am, John Larkin wrote:
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Epoxy is not great with heat though. What product do you use?

Clifford Heath

Re: Heatsink, just don't drop it on concrete
On Wed, 19 Jun 2019 08:28:17 +1000, Clifford Heath

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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  

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Re: Heatsink, just don't drop it on concrete

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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.
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Re: Heatsink, just don't drop it on concrete
On Fri, 21 Jun 2019 12:35:26 -0400, snipped-for-privacy@notreal.com wrote:

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


--  

John Larkin         Highland Technology, Inc

lunatic fringe electronics  


Re: Heatsink, just don't drop it on concrete
On Fri, 21 Jun 2019 09:45:07 -0700, John Larkin

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

Re: Heatsink, just don't drop it on concrete
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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
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Re: Heatsink, just don't drop it on concrete
On Fri, 21 Jun 2019 12:21:01 -0500, "Tim Williams"

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


Re: Heatsink, just don't drop it on concrete
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Compared to what?  Great how?

Aluminum metal is so much more conductive than needed, it doesn't really  
matter, in terms of board-level heatsinks.

Alumina is perfectly traditional in many products.  Must be good for  
something.

Tim

--  
Seven Transistor Labs, LLC
Electrical Engineering Consultation and Design
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Re: Heatsink, just don't drop it on concrete
On Sat, 22 Jun 2019 02:04:32 -0500, "Tim Williams"

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AlN, Al, or any of the usual suspects.
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Huh?
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We were discussing ceramics.

Re: Heatsink, just don't drop it on concrete
On Fri, 21 Jun 2019 23:19:11 -0400, snipped-for-privacy@notreal.com wrote:

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Because it looks cool? Because it makes things sound better?


--  

John Larkin         Highland Technology, Inc
picosecond timing   precision measurement  

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