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Proper Application
Method |
| Figure 1 - Correct application amount |
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Figure 1-Proper Application of
an approximately 5.0-5.5 mm bead on center example on
left utilizing a synthetic IHS. The primary reason
we recommend a compression type spreading is that we
have found that the best results are attained with a
compression type spreading.
The grease spreads uniformly and
minimizes the introduction of air bubbles in to the
thermal interface joint, a potential cause of grease
failure that will affect long term reliability which
can be observed in the following
examples | |
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Figure 2 - Full mount
coverage |
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Figure 2-Here we have the
simulated IHS clamped between two slides with 50 psi
force applied with the 5.0mm-5.5mm bead application
spread pattern by compression.
Simulated mount was heated
heated in an oven @ 100C for 20 min to flow the
compound. Paste is smooth and even with
no visible air
pockets. | |
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Wrong Methods With an
Explanation | |
| Figure 3 - Example of Air Pocket
formation |
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In this example IC
Diamond was applied between two glass slides
and stress tested in an oven @ 150C for 20 hours.
Applied 5mm bead of ICD. Photoshopped to
highlight the air bubble
halo.
Note the
halo of air bubbles, this is why it is important to
apply enough compound, because as the paste thins it
spreads it reaches a maximum zone where air is reformed
into the paste application between the sink and
IHS
In essence you need enough compound to
extend the air pocket zone outside the area of
IHS contact | |
| Figure 4 - Competition
grease air pocket example |
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Not unique to IC
Diamond Figure 4 is a compression spread
of a popular competition compound to show the halo
effect is not limited to IC Diamond. Demonstrated here
between 2 glass slides and heated @ 125C for 1
hour clamped under pressure it shows
initial void formation. The Slide moved a bit by
accident, but the air pockets are still visible as the
lighter gray spot just inboard of the outer
edge.
Air pockets that were not
visible in the initial application expanded under heat
and pressure so the TIM Joint thickness now has an
element of the mount riding on a cushion of air with the
potential to affect thermal
performance. | |
| Figure 5 - Early grease failure |
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This is a second popular
competition grease mounted between two glass slides and
run @ 150C for 20 hours under accelerated
testing.
Here the air pockets have
migrated together and formed larger voids. the halo is
still visible.
This effectively is an early
failure of the
compound. | |
| Figure 6- Incorrect 3.5 mm bead
application |
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| This is approximately a 3.5
bead application and not enough to do the Job as it
allows the air bubble zone to form inside TIM
joint | |
| Figure 7 - "Raw Halo" with trapped
air |
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Here is the same 3.5
bead clamped between two slides. note the TIM
application was light with the formation of the
extensions which have closed in on itself creating the
halo effect on the edges where the "flowers" or
"extensions" have reformed trapping air. The "Raw Halo"
is clearly
visible | |
| Figure 8- Full spread |
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| Figure 8 is the commonly
used method that covers the entire
IHS | |
| Figure 9 - Full spread with Air
Pockets |
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| Same application as above
clamped between two glass slides note the white spots
these are the initial air bubbles. Again the issue
or problems with air bubbles is that air is very
difficult to compress and will expand under heat and
pressure which will displace the TIM with
voids | |
| Figure 10 - Incorrect line method |
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| Line Application of IC Diamond.
Generally single, multiple lines, multiple beads are not
recommended as they have a tendency to introduce more
air as the separate applications join together closing
off opportunities for the air to
escape. | |
| Figure 11 - Incorrect line spread
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| Line application Of IC Diamond
between two glass slides shows good coverage top to
bottom, however side to side the formation of
cauliflower like extensions that can be seen to be
closing or reforming in on itself trapping
air. | |
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| Figure 12 - Example of manual grease
wetting |
Application
Recommendation |
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| A component to paste
application to be mindful of is the roughness of
the mating surfaces. If you have only lapped up to an
800 grit or less it may be necessary to manually wet
the surface the surfaces prior to applying a bead of
compound. In this example a light haze of compound was
applied to push out any air bubbles or air pockets that
may have found purchase in scratches or surface
finish | |
