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From: Martin Brown <'''newspam'''@nonad.co.uk>
Newsgroups: sci.electronics.design
Subject: Re: silicone grease
Date: Sun, 31 Mar 2024 13:25:02 +0100
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On 30/03/2024 18:14, John Larkin wrote:
> Give a nice flat mosfet package and a flat heat sink, I wonder how
> much benefit accrues from adding silicone grease. It's really messy in
> production and it's hard to confirm proper application. A little
> googling didn't provide hard numbers.
> 
> I'm thinking a big-die TO-220 fet, bolted to a copper CPU cooler, AlN
> or mica insulator, no grease, 40 watts. I guess I'll have to try it.

ISTR on one of the overclocking hacker CPU cooling sites someone tried 
everything from dry to cooking oil and engine oil. The marginal best was 
some exotic "liquid metal" silver loaded brand I have never heard of and 
the worst by a long way was dry.

The biggest change was from dry to some sort of heat exchange medium is 
by preventing an air gap. It was a significant difference too.

The problem is that your flat surfaces are not exactly flat so that the 
direct metal contact area can actually be quite small if there is any 
surface roughness. Air is a rather good insulator and metals don't 
radiate well at all. Silicon grease prevents air gaps and anything 
similar will do the same job. It is just that silicon oils and greases 
are less inclined to evaporate or go rancid and corrode your parts.


-- 
Martin Brown