CPU heatsink/fan help!

Silicone should not break down at all, since it is "neutral". That's why
they are using it for breasts implants.
--

Matt <mspa @bellsouth.net>
: I agree, but have one question.  The 1 oz. tube would last a lifetime
: with respect to volume alone,  but I would think that the product will
: break down chemically after a few years.  Could someone with knowledge
: in this area post in response?  Thanks.

On 4 May 1997 15:20:00 GMT, "John" <x @digicron.com> wrote:

If that`s the case, then why all the law suits concerning breast
implants?

If I'm not mistaken, the Radio Shack thermal goo is silicon grease with
zinc oxide particles mixed in.  The same sort of goo is used between a
semiconductor and its heat sink in all sorts of electronic equipment.  

In my experience, after a few years, the grease thickens (breaks down
chemically?), leaving the zinc oxide.  I believe that the grease is not
that important to the heat transfer, but the many tiny grains of zinc
oxide fill small gaps and provide a large number of small thermal paths
of low resistance.  When combined, the large number of small paths
create a large one.  In emergencies, I have replaced the semiconductor
without replacing the goo, relying only on the leftover dried stuff on
the heat sink, and it worked quite well.

There are thermally conductive glues and pads (adhesive and
non-adhesive) that serve the same purpose.  If you have a CPU chip with
a factory installed heat sink, you can bet that the thermal
conductivitity of the adhesive was an important consideration.  I have
my doubts about the thermal properties of the adhesive used on some
after-market heat sinks.  However, my biggest concern about the
after-market heat sinks is that the adhesive always fails after a few
years, leaving a CPU with no heat sink and a loose piece of metal to
move around and cause electrical shorts.  

--
Jerry Oakley, Chief Engineer            Voice/Fax:  (972) 613-0413
B & A Computer                              >>>>>> NEW E-MAIL ADDRESS:
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Mesquite  TX  USA  75150-4846

  I see no smileys here, so I'll assume you're serious.  It is not that
  the silicone "breaks" down.  But it must be the thinnest possible coat
  that still allows no voids.  If the system is in a tower case
(upright)
  it is possible for a thin coat to separate over time without a clamp-
  down fansink.  The clamp-down heatsink also halps squish the compound
  evenly, also minimizing voids.

----
  Keith R. Williams
  k @ibm.net

  It is *not* an adhesive.  It is normally a silicon grease and can be
  found in any Radio Shack.  It's benefit is not that it's a great
thermal
  conductor, but it is far better than air,  It seals the voids between
  the chip and the heatsink/fansink.  For this reason, this stuff must
  be used sparingly.  A very thin coat is best (a 1 oz. tube will last
  a lifetime).

  Please!  Clamp-down only.  The clip-on's and stick-on's don't hold
  tightly enough to eliminate/prevent voids in the thermal compound.

----
  Keith R. Williams
  k @ibm.net

The glue they use is either a thermal adhesive or thermal adhesive pad.
Using anything else will result in poor heat transfer between the CPU
and heatsink.

The only place you'll find thermal adhesive is through an electronics
distributor like Allied, Digikey, or Mouser. Some of the better full
service electronics supply houses should have it.

Either that or replace the heatsink/fan with a clip-on/strap-down type.

Tom Mosher
sds mark II
tmos @isource.net