[TriEmbed] Conductivity pad thickness

[John Wettroth]

This is confusing- you should use the "thinnest" pad that you can get away with.
Only enough to make up for any mechanical surface inconsistencies.  Thermal
Conductivity are the units they use -W/mK, the more common unit is Thermal
Resistance which is the inverse of conductivity (just like electronics).  You
can think of heat sink materials as a series of resistors that are taking the
junction temperature though a series of interfaces to ambient.  You want the
lowest resistance path to give you the lowest temp rise.  When you invert their
conductivity, you'll get Resistivity with units of mK/W, this is what you want
to minimize.  Thermal Resistance uses a theta symbol and is usually dimensioned
in W/deg C, though W/K would be more correct.

If things are pretty flat, .5mm should be fine, this is .02 inches.
I noticed they had some precut units for some common GPU's (3080, etc.) though
pricey?

A common error people make with thermal pastes of all types is to use too much.
"The bigger the blob, the better the job" philosophy of new solderers.  All you
want to do is fill the tiny gaps and get the two surfaces in intimate contact.
Nicely machined and polished surfaces would be the best- but no one but NASA has
the dough for that.
Good luck.

Regards,
John M. Wettroth
E: jwet at mindspring.com
M: (919) 349-9875 
H:  (984) 329-5420

-----Original Message-----
From: TriEmbed <triembed-bounces at triembed.org> On Behalf Of Mauricio Tavares via
TriEmbed
Sent: Thursday, December 14, 2023 10:37 PM
To: TriEmbed Discussion <triembed at triembed.org>
Subject: [TriEmbed] Conductivity pad thickness

I need to replace the gpu card in my desktop and was going to take the
opportunity and try to use a conductivity pad instead of the goo. Last
time I used it was in heat sinks on my Rpi4, which were bits from what
I had used in my 3D printer. It worked I guess, but this time we are
talking about GPU and I would like not to half ass it.

So I was looking at https://kriticalpads.com/full-sheets and did not
realize they sold them by the thickness, with the thicker being
supposedly the most conductive. How do I figure out how thick I need?
Just the thickest one I can shove in place? I was also thinking about
the merit of using them in a laptop, where space is at a premium on a
good day.

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