Re: silicone grease

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