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Re: [Amps] SSPA & Heatsink Compounds

To:, Manfred Mornhinweg <>
Subject: Re: [Amps] SSPA & Heatsink Compounds
From: <>
Date: Wed, 11 Dec 2013 19:40:19 +0000
List-post: <">>

I have build several solid state amplifers, including a 1KW HF amp that I am 
currently using on a daily basis.  I use Artic Silver.  I found that it is 
really important to first of all have a flat surface between the copper heat 
spreader and the aluminum heatsink.  I have always had these surfaces milled.  
The milling cost more than the heatsink, but it is worth it.  Then put a very 
thin layer of Artic Silver between the copper heat spreader and the heatsink, 
and underneath the MOSFETS.  More is not better, use a line layer.  I use a 
roller to spread the Artic Silver.

---- Manfred Mornhinweg <> wrote: 
> Paul,
> > I'm getting around to my 2 meter kilowatt SSPA.  My question is which of
> > the multitude of heatsink compounds do you recommend?  I have read some of
> > the comparisons mostly dealing with CPU cooling.  But, would like some
> > input from piratical experience.  The silver formulations seem to do a bit
> > better.
> When I looked for data on these compounds, the best rated one I could 
> find was Arctic Silver 5. It's about twice as heat conductive as the 
> best ceramic-based compounds, according to its data sheet. But I haven't 
> yet measured whether those claims are true.
> Between the different ceramic based compounds, there are some large 
> differences too. They are not all equal! I found differences up to a 
> ratio of ten between them! Check the specs and compare before you buy.
> > In addition, I am assuming that I want a layer of the stuff between the
> > copper heat spreader and the heatsink?
> Yes. Assuming the spreader is large, and lies very flat against the 
> heatsink, a decent grade ceramic compound is good enough there - but a 
> better compound is always better! Between the transistors and the 
> spreader instead, really the best is soldering! Solder is about 8 times 
> better than the best silver particle compound. If it's not practical to 
> solder the transistors to the spreader (as is often the case), use the 
> best compound you can find. You need only a tiny quantity there.
> And if your transistors are expensive, do the math about their cooling 
> BEFORE you build that amplifier! If they are cheap, or if you have a 
> free supply of them, you can use the empiric method and just see if they 
> survive... ;-)
> Manfred
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