[hpsdr] Munin heat sink and spreader

[Helmut, DC6NY]

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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