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'[EE] Copper Heat Sink'
2005\01\17@142709 by Lawrence Lile

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Once upon a time, I had a nice DOC on using copper clad boards as heat
sinks.  Alas, I can't locate it anymore.

Does anyone have a guideline for using double-sided 1 ounce copper PCB as a
heatsink??  I am going to be using an IRF3170L MOSFET, which has a TO-262
package (about the same size as a TO-220, bit smaller tab)  each dissipating
about 5 watts.  The transistor has a thermal resistance junction to case of
0.75 degree C per watt.  Instinct says that we should be able to dissipate 5
watts through a board, but I need to have numbers to back that up.

--Lawrence Lile
http://www.projsolco.com
Electronic Solutions

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2005\01\17@144303 by Rob Young

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----- Original Message -----
From: "Lawrence Lile" <spam_OUTlawrencelileTakeThisOuTspamhotmail.com>
To: <.....piclistKILLspamspam@spam@mit.edu>
Sent: Monday, January 17, 2005 1:26 PM
Subject: RE: [EE] Copper Heat Sink


{Quote hidden}

Not exactly the answer you are looking for but go to National Semi's web
site and look at some of their "Simple Switcher" parts.  The ones I've used
have several tables and charts comparing the Rtheta of copper clad to heat
sinks.

Rob Young
rwyoungspamKILLspamieee.org

2005\01\17@170232 by steve

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On 17 Jan 2005 at 13:26, Lawrence Lile wrote:

> Once upon a time, I had a nice DOC on using copper clad boards as heat
> sinks.  Alas, I can't locate it anymore.

Infineon have a paper called
"Thermal Resistance Theory and Practice" that covers it quite well.
There is also an online calculator at
http://www.frigprim.com/online/therm_terr.html that may help.

Steve.


==========================================
Steve Baldwin                          Electronic Product Design
TLA Microsystems Ltd             Microcontroller Specialists
PO Box 15-680, New Lynn                http://www.tla.co.nz
Auckland, New Zealand                     ph  +64 9 820-2221
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=========================================



2005\01\17@174728 by Russell McMahon

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> Does anyone have a guideline for using double-sided 1 ounce copper
> PCB as a heatsink??  I am going to be using an IRF3170L MOSFET,
> which has a TO-262 package (about the same size as a TO-220, bit
> smaller tab)  each dissipating about 5 watts.  The transistor has a
> thermal resistance junction to case of 0.75 degree C per watt.
> Instinct says that we should be able to dissipate 5 watts through a
> board, but I need to have numbers to back that up.

Very relevant - albeit not the full story.
Micrel application hint 17
Designing PC board heat sinks

       http://www.micrel.com/_PDF/App-Hints/ah-17.pdf

Table 5 is of relevance

       http://www.asat.com/products/library/bg1002.pdf

This will be of interest

       http://www.maxim-ic.com/appnotes.cfm/appnote_number/862


       RM

2005\01\17@191658 by Mike Harrison
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On Tue, 18 Jan 2005 11:47:20 +1300, you wrote:

>> Does anyone have a guideline for using double-sided 1 ounce copper
>> PCB as a heatsink??  I am going to be using an IRF3170L MOSFET,
>> which has a TO-262 package (about the same size as a TO-220, bit
>> smaller tab)  each dissipating about 5 watts.  The transistor has a
>> thermal resistance junction to case of 0.75 degree C per watt.
>> Instinct says that we should be able to dissipate 5 watts through a
>> board, but I need to have numbers to back that up.
>
>Very relevant - albeit not the full story.
>Micrel application hint 17
>Designing PC board heat sinks

Unless the PCB is pretty big or you have forced air, I think 5 watts is unrealistic.
I start worrying at anything over a watt.


2005\01\17@202744 by Bob Axtell

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I've noticed that  4-layer PCBs which have at least GND as a plane, seem to
handle heat well. Otherwise, PCB's make poor heat sinks.

--Bob

Mike Harrison wrote:

{Quote hidden}

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2005\01\17@204023 by SO-8859-1?Q?Hern=E1n_Freschi?=

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maybe in a future Intel will release Pentium 23 or something like
that, with reduced power dissipation which will cool itself on the
mobo ground plane. I can't wait to throw my cpu cooler out the window.

Seriously, even if you had forced air through the pcb, it will get
dirty and lose a lot of thermal conductivity. I wouldn't rely on that.
people expect circuits, especially PIC based which are supposed to be
reliable (like in a control system), to not to need active cooling. So
i'd avoid that if it were possible


On Tue, 18 Jan 2005 00:21:22 +0000, Mike Harrison <mikespamspam_OUTwhitewing.co.uk> wrote:
{Quote hidden}

> -

2005\01\17@214544 by Russell McMahon

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>> Once upon a time, I had a nice DOC on using copper clad boards as
>> heat
>> sinks.  Alas, I can't locate it anymore.

In case you missed it, you really want to read this

       http://www.frigprim.com/articels/thermterr_1.html

Links from and is related to the page that Steve referred to.



       RM

2005\01\17@214546 by Russell McMahon

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> Infineon have a paper called
> "Thermal Resistance Theory and Practice" that covers it quite well.


       http://www.infineon.com/cmc_upload/migrated_files/document_files/Package/smdpack.PDF

also via

       http://archive.chipcenter.com/power/powa154.html



       RM


2005\01\18@133110 by Lawrence Lile

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So much for instinct.  The online calculator posted by Steve throws plenty of water on this idea.  Heat sinks it is!

--Lawrence Lile
Electronic Solutions
http://www.projsolco.com

>
>Unless the PCB is pretty big or you have forced air, I think 5 watts is
>unrealistic.
>I start worrying at anything over a watt.
>
>

2005\01\18@133642 by Lyle Hazelwood

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>So much for instinct.  The online calculator posted by Steve throws plenty
>of water on this idea.  Heat sinks it is!
>
>--Lawrence Lile

Hmm, yes, the water should be enough to make the difference.
But I would think heatsinks are less complicated than water cooling.

8^)

(Sorry Lawrence, too much time on my hands today) 8^)

Lyle
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2005\01\18@134109 by Lawrence Lile

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Thanks Russel, This paper says that 1.2 watts is the practical limit, and that above 0.8 watts PCB cooling area starts going up rapidly.  Anything over a watt (as someone else said) makes one get nervous.  This explains why my attempt at cooling a 2 watt resistor one time, by adding some PCB copper area under it, wasn't very effective.  I tried it just for grins, but no calculations.


--Lawrence Lile
Electronic Solutions
http://www.projsolco.com

{Quote hidden}

2005\01\18@141916 by Lawrence Lile

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Lyle, all I can say is:  "Aaarrgh"  ;-)

{Quote hidden}

2005\01\18@150950 by Dwayne Reid

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At 11:30 AM 1/18/2005, Lawrence Lile wrote:

>So much for instinct.  The online calculator posted by Steve throws plenty
>of water on this idea.  Heat sinks it is!
>
>--Lawrence Lile
>Electronic Solutions
>http://www.projsolco.com

You mean: "So much for instinct.  The online calculator posted by Steve
throws plenty of STEAM on this idea.  Heat sinks it is!"

(same excuse as Lyle <grin>  )

dwayne

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2005\01\19@090019 by Lawrence Lile

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D'oh!!!

>
>You mean: "So much for instinct.  The online calculator posted by Steve
>throws plenty of STEAM on this idea.  Heat sinks it is!"
>
>(same excuse as Lyle <grin>  )
>
>dwayne
>
>--
>Dwayne Reid   <EraseMEdwaynerspamplanet.eon.net>
>Trinity Electronics Systems Ltd    Edmonton, AB, CANADA
>(780) 489-3199 voice          (780) 487-6397 fax
>
>Celebrating 20 years of Engineering Innovation (1984 - 2004)
>  .-.   .-.   .-.   .-.   .-.   .-.   .-.   .-.   .-.   .-
>     `-'   `-'   `-'   `-'   `-'   `-'   `-'   `-'   `-'
>Do NOT send unsolicited commercial email to this email address.
>This message neither grants consent to receive unsolicited
>commercial email nor is intended to solicit commercial email.
>
>

2005\01\19@173308 by Peter L. Peres

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On Tue, 18 Jan 2005, Lawrence Lile wrote:

> Thanks Russel, This paper says that 1.2 watts is the practical limit, and
> that above 0.8 watts PCB cooling area starts going up rapidly.  Anything over
> a watt (as someone else said) makes one get nervous.  This explains why my
> attempt at cooling a 2 watt resistor one time, by adding some PCB copper area
> under it, wasn't very effective.  I tried it just for grins, but no
> calculations.

You can cool it by mounting it on 'standoff' tubes (brass usually).
These can be finned at the top.

There is also a 'mushroom' style heatsink that can be screwed directly
onto a TO220 etc mounting hole. I saw it in some equipment and have been
looking for something like this ever since.

Another trick is to mount the board with the parts flush with the bottom
(metal) plate of the casing, with some thermal compound for contact.

Peter

2005\01\20@071804 by Douglas Wood

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There's a PCB layout technique called "via stitching" that is basically a
number of regularly spaced plated-through vias (holes) in the pad's area
that connects copper between the two sides (assuming a double-side PCB; it
was also work multiple layer boards). During board assembly, the via are
filled with paste (you could also hand solder the vias, although I not sure
if wave soldering would fill all of the vias). This adds additional metal to
the heat sink. I use this method on all of my voltage regulators and power
transistors (TO-220, TO-252/D-PAK, TO-263, SOT-23, etc.). If you'd like to
see a photo of what this looks like, please let me know.

Douglas Wood

{Original Message removed}

2005\01\20@091006 by M. Adam Davis

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It's also a pain to solder/desolder small components to/from.  Makes for
a very good heat sink.

Computer motherboards use these liberally around the switching
regulators that power the CPU.  The negative end of the filtering caps
(you know, the caps that fail and have to be replaced?) usually ends up
in one of these via stitched areas.

But it's not so bad that I'm going to throw away essentially free
computers either...

-Adam

Douglas Wood wrote:

{Quote hidden}

> {Original Message removed}

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