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'[EE] Heatsink SMT LED?'
2007\02\11@170535 by Brooke Clarke

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Hi:

If a Luxeon K2 LED is mounted on the top side of a PCB what's the best
strategy to get the heat to the bottom side?
For example is it better to use as many through holes as possible and
fill them with solder, or use a larger hole and solder in a copper wire?
Or maybe make a custom copper plug and solder a number of them?

The K2 has a higher operating temperature than the standard emitters
that run on 350 ma and can be run at anywhere between 350 and 1000 ma
allowing a trade off in heat sinking and output.  The LM3404 is rated to
1 Amp.

Have Fun,

Brooke Clarke

--
w/Java http://www.PRC68.com
w/o Java www.pacificsites.com/~brooke/PRC68COM.shtml
http://www.precisionclock.com

2007\02\11@235917 by Bob Axtell

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Brooke Clarke wrote:
> Hi:
>
> If a Luxeon K2 LED is mounted on the top side of a PCB what's the best
> strategy to get the heat to the bottom side?
> For example is it better to use as many through holes as possible and
> fill them with solder, or use a larger hole and solder in a copper wire?
> Or maybe make a custom copper plug and solder a number of them?
>
>  
While solder DOES pass heat it does NOT do it well; silver then copper
(in that order) conduct heat
MUCH better.  I would try to fit a rivet made of silver first, next
install thick wires of copper, with
solder used just to hold everything together.

--Bob

{Quote hidden}

2007\02\12@011603 by James Nick Sears

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On Feb 11, 2007, at 11:59 PM, Bob Axtell wrote:

> Brooke Clarke wrote:
>> Hi:
>>
>> If a Luxeon K2 LED is mounted on the top side of a PCB what's the  
>> best
>> strategy to get the heat to the bottom side?
>> For example is it better to use as many through holes as possible and
>> fill them with solder, or use a larger hole and solder in a copper  
>> wire?
>> Or maybe make a custom copper plug and solder a number of them?
>>


I've never worked with the K2, but with the regular Luxeon III  
emitter, I've had good long term results with the layout shown here  
http://www.annehong.com/itp/livingArt/livingArt12.htm near the top of  
the page, which uses the many small plated holes approach.  4 of  
those boards for a total of 32 emitters, each placed in a drop of  
arctic silver thermal grease, are mounted in a retired streetlamp at  
indoor ambient temperatures, but no significant airflow out of the  
light fixture.

If you're interested, the whole piece can be seen here:
artmagnitude.com/

-n.

2007\02\12@011737 by James Nick Sears

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On Feb 11, 2007, at 11:59 PM, Bob Axtell wrote:

> Brooke Clarke wrote:
>> Hi:
>>
>> If a Luxeon K2 LED is mounted on the top side of a PCB what's the  
>> best
>> strategy to get the heat to the bottom side?
>> For example is it better to use as many through holes as possible and
>> fill them with solder, or use a larger hole and solder in a copper  
>> wire?
>> Or maybe make a custom copper plug and solder a number of them?


Just remembered another detail about those PCBs from the last post -  
they were spec'ed with 2oz copper.

-n.

2007\02\12@013146 by William Chops Westfield

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On Feb 11, 2007, at 8:59 PM, Bob Axtell wrote:

> I would try to fit a rivet made of silver first...

Hmm.  Does anyone make shouldered copper slugs that are carefully
T-shaped to fit common PCB thicknesses for this purpose?  Something
with a 4mm*1.6mm shank and a thin 5mm*0.4mm head or so ?

If you need silver rivets, you're in serious trouble.  Copper should
be plenty good enough depending on what you have on the other side.
And solder, while it's conductivity is not good compared to copper,
conducts heat a couple hundred times better than FR4 PCB material,
and better than Aluminum Oxide (used in thermal grease, etc) as well.

BillW

2007\02\12@014207 by William Chops Westfield

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On Feb 11, 2007, at 10:15 PM, James Nick Sears wrote:

> http://www.annehong.com/itp/livingArt/livingArt12.htm

That's sort of interesting.  Is the 'finned' PCB layout
actually useful?  Fins on a heatsink convect to air, but I
would have thought a solid copper area would be better on a
flat PCB...

BillW

2007\02\12@021926 by James Nick Sears

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On Feb 12, 2007, at 1:42 AM, William Chops Westfield wrote:

>
> On Feb 11, 2007, at 10:15 PM, James Nick Sears wrote:
>
>> http://www.annehong.com/itp/livingArt/livingArt12.htm
>
> That's sort of interesting.  Is the 'finned' PCB layout
> actually useful?  Fins on a heatsink convect to air, but I
> would have thought a solid copper area would be better on a
> flat PCB...

The fins were more for aesthetic reasons.  Although the light is  
normally closed, during the initial demos, I did a lot of opening the  
lid and showing off of the electronics themselves.  I wouldn't argue  
your thinking that solid copper would be slightly more effective,  
roughly proportional to the additional surface area.

-n.



2007\02\13@063938 by Howard Winter

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On Sun, 11 Feb 2007 22:31:37 -0800, William "Chops" Westfield wrote:

>...
> Hmm.  Does anyone make shouldered copper slugs that are carefully
> T-shaped to fit common PCB thicknesses for this purpose?  

I seem to remember Harwin making these, *many* moons ago.  They were made in a head-to-toe strip so you could insert the end one, solder it, and
then break off the rest of the strip.  Much easier than trying to hold the darned things individually...

> Something with a 4mm*1.6mm shank and a thin 5mm*0.4mm head or so ?

I don't think they were as big as that, maybe 2.5mm x 1mm shank which was tapered, head about 2mm across, but I can't remember exactly.  They
weren't so much for thermal use as to act as vias to allow non-PTH double sided boards to be hand-soldered.

Cheers,


Howard Winter
St.Albans, England


2007\02\13@072411 by Dan Smith

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On 2/13/07, Howard Winter <spam_OUTHDRWTakeThisOuTspamh2org.demon.co.uk> wrote:
> On Sun, 11 Feb 2007 22:31:37 -0800, William "Chops" Westfield wrote:
> > Hmm.  Does anyone make shouldered copper slugs that are carefully
> > T-shaped to fit common PCB thicknesses for this purpose?
>
> I seem to remember Harwin making these, *many* moons ago.  They were made in a head-to-toe strip so you could insert the end one, solder it, and
> then break off the rest of the strip.  Much easier than trying to hold the darned things individually...

You're right about Harwin making them - I used them a long time ago
too, but they still seem to be available.  I think they were called
track pins.

Harwin Part Number T1559-01 - drawing available from
<http://www.harwin.com/include/downloads/drawings/T15XX.PDF>

Dan

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