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Thermal Conducting Compound/Tape
To allow the most effective conduction
between the heatsink and the CPU, a thermal conducting compound is used
between the CPU die and the heatsink. This is because the more contact
between the die and the heatsink, the better the transfer of heat will
be.
Even flat objects that appear to
be in full contact might have limited points of contact, due to the
roughness of the surfaces at a microscopic level. It’s estimated
that only 1% of the surfaces may actually be in contact when two flat
metal parts touch each another! The remaining space is filled with air,
which is a poor thermal conductor. Thermal compound fills in these
gaps of contact and greatly increases the efficiency of the heatsink.
Proper use of a thermal compound
between the CPU and heatsink is absolutely necessary for proper cooling
of the CPU. If your CPU and heatsink instructions tell you to use a
thermal compound, do not omit this step.
Thermal compound comes in two forms.
First is thermal grease, which looks just like any other thick liquid.
If thermal grease is used, you simply place a drop of thermal grease
on the die before installing the heatsink. Use a drop just about the
size of a small pea and place it at the center of the die. As the heatsink
is installed, it is pressed down and the thermal grease will compress
and flatten out.
Second, and a better, less messy
method, is a thermal tape applied to the heatsink that comes with the
heatsink (Figure 29
shows the thermal compound on the bottom of the heatsink). Examine your
heatsink and your heatsink instructions to see which method is used.
If your heatsink has a strip of thermal tape on it, you don’t need
to use thermal grease. The tape is used instead of the grease.
If your heatsink has a thermal tape
applied to it, remove the cover of the tape just before you install
the heatsink. Don’t allow the thermal tape to be exposed for a
long period of time before doing the installation. You don’t want
it to attract dirt.
If you ever need to remove the heatsink
from the CPU, which originally had thermal tape and then reinstall the
same CPU and heatsink (you probably will never need to do this), you’ll
need to scrape off all of the thermal compound from the heatsink. Because
the material will fill in the pores at the microscopic level, you’ll
never remove all of the old material. But, try to remove all
visible material. Then, you’ll apply new thermal material.
For the Athlon, AMD.com has a list of approved thermal materials, including
Bergquist HF225UT (See AMD’s Builder’s Guide For Desktop/Tower
Systems, Document 26003A for other thermal materials).
Incidentally, AMD only approves phase-change
thermal material. So, don’t use ordinary thermal grease of an unapproved
type. If you purchase your CPU in a retail-box version, it will come
with a proper heatsink and an appropriate thermal compound inside the
retail box.
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How to Build Your Own PC (http://www.PCGuide.com/byop/) on PCGuide.com
Version 1.0 - Version Date: May 4, 2005
Adapted with permission from a work created by Charlie Palmer.
PCGuide.com Version © Copyright 2005 Charles M. Kozierok. All Rights Reserved.
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