[hpsdr] Munin heat sink and spreader

[Mike Seguin]

Between the device and copper spreader on all the LDMOS kW amps I've 
built I use a THIN coat of Artic Silver 5.

http://www.arcticsilver.com/as5.htm

Thin means a small dot and then I use a razor blade to spread it. It 
should be so thin that you can actually see the flange. The idea is to 
just fill small gaps/pockets.

I also check that the spreader is flat and on the large devices like NXP 
BLF-578 etc, check the device. The flange may not be really flat.

Lay very very fine grit paper on glass and move the device in a figure 8 
gently to flatten it out. You're trying to reduce the high spots.

No device failures here yet....

Mike

On 10/10/2013 7:13 AM, Helmut, DC6NY wrote:
> ***** High Performance Software Defined Radio Discussion List *****
>
> Hi Mike,
>
> you are right with 'Wiedemann-Franz'. That's the reason why I no longer use
> this standard thermal conductance paste. Between the final transistors and
> the copper spreader a liquid silver emulsion works fine. Between the copper
> spreader and the heat sink I got good results with liquid copper used e.g.in
> the repair engine blocks. Perhaps
> http://www.polymermetal.com/downloads/tec/e_tec_016.pdf can help.
>
> 73, Helmut, DC6NY
>
>
> -----Ursprüngliche Nachricht-----
> Von: hpsdr-bounces at lists.openhpsdr.org
> [mailto:hpsdr-bounces at lists.openhpsdr.org] Im Auftrag von AA8K73 GMail
> Gesendet: Donnerstag, 10. Oktober 2013 12:14
> An: HPSDR
> Betreff: Re: [hpsdr] Munin heat sink and spreader
>
> ***** High Performance Software Defined Radio Discussion List *****
>
>
> Thanks gentlemen.
>
> I was thinking of the metal particles providing the thermal conductivity
> (Wiedemann–Franz law), but I suspect that the per cent of contact area is
> small.
>
> When I held the spreader and sink together to check for fit, I noticed the
> gap and turned the spreader over to see if it was bowed.  I used a metal
> straight edge against the spreader and the spreader was flat.  Looking at
> the reflections in the spreader, I couldn't find any optical distortion.  I
> am impressed with the quality of that spreader.
>
> Longitudinally, the heat sink is very straight.  It just curves
> transversely.  Thanks for the confirmation Berndt.
>
> I used to maintain copper resistance-welding fixtures (ignitrons; too long a
> duration and they would open the 400 amp line fuses), and used lathe, mill,
> surface grinder, and shaper.
>
> I'm concerned about someone else removing too much material in search of
> flatness.  Too deep and it would require a shim to match the transistor to
> board height requirement; and make two more thermal interfaces.  Buying
> another drilled and tapped heat sink would be costly.
>
> I hope to carefully file the sink and take < 1 mm away.
>
>
> 73,
> Mike - AA8K
>
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-- 

73,
Mike, N1JEZ
"A closed mouth gathers no feet"


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