On Fri, 3 Sep 2010 06:24:11 +0100, Mike Tomlinson
wrote:
Have you tried applying the white stuff to both surfaces, then scraping
it off with the edge of a card? That will fill in any valleys on both
surfaces, and you should get a good thermal bond with the minimum of
compound.
This is the method that AS suggest using, by the way.
I've always suspected that it's a conspiracy by the manufacturer to
consume more expensive Artic Silver. Kinda like washing your hair
twice with "pH balance" shampoo.
The best heat tranfer between heat sink and CPU is metal to metal
contact, with no grease. The problem is that neither the heat sink or
CPU lid are flat and have pits, holes, gouges, lumps, cavities, and
other problems that prevent good contact. Even without these problem,
and with a mirror finish base, the typical warped package and
non-stress relieved heat sink, will not produce proper metal to metal
contact (without extreme mechanical pressure). My guess(tm) is that a
typical "brushed" aluminum heat sink to a Pentium 4 package might have
30% or less metal to metal contact. This sucks.
The idea is to fill the pits, holes, gouges, lumps, cavities, etc with
something thermally conductive, thus eliminating the need for mirror
finished and flat CPU's and heat sinks. The trick is to only fill the
pits, holes, gouges, lumps, cavities, etc and still retain as much
metal to metal contact as possible. That's not going to happen if you
use too much. As a clue, see the thermal resistance spec for Artic
Silver at:
http://www.arcticsilver.com/as5.htm
Thermal Resistance:
0.0045°C-in^2/Watt (0.001 inch layer)
Notice the 0.001 inch (0.025mm) layer. That's really really really
thin. So thin, that you could probably not even see it on the surface
because most of the stuff is in the pits, holes, gouges, lumps,
cavities, etc. If it had been specified with a thicker layer, the
thermal resistance would have been much worse.
It's probably a good idea to smear on some Artic Silver on both sides
of the junction, but then wipe off everything except what's in the
pits, holes, gouges, lumps, cavities, etc leaving as much metal to
metal contact as possible. If you're dealing with a badly warped or
an unpolished casting, then a little more grease might justifiable.
However, packing it on in a thick layer, but doing both sides, is a
waste.
--
Jeff Liebermann
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060
http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558