I347-AT4 Datasheet, PDF (142/148 Pages) Intel Corporation – Intel® Ethernet Network Connection I347-AT4 Datasheet

I347-AT4 — Thermal Design Recommendations
Figure 7.4. TIM Function
7.7.2.1
TIM Types and Performance
There are several different types of TIMs, such as:
• Greases — A tacky, liquid like substance.
• Phase Change Materials (PCM) — A material that starts out as a dry film and changes to a liquid
above a specific temperature.
• Gap Pads — Compressible (typically) non-liquid material designed to fill a large gap between the
heat sink and package.
• Pressure Sensitive Adhesives (PSA's) — A permanent adhesive applied to the bottom of a heat sink.
PCMs and greases tend to be the most effective as they offer the thinnest bond lines with great
wetting/spreading characteristics. The effectiveness of each of these different material types is
governed primarily by the following:
• Material Wetting/Filling Characteristics — determines how well the material flows to fill in the small
gaps between interfacing surfaces. The more completely the material fills the voids at the interface,
the lower the resulting thermal resistance.
• Bond Line Thickness — the resulting thickness of material between the heat sink and package
surface once the heat sink has been installed and the material has heated to its equilibrium
temperature. Greases and phase change materials tend to flow after they have been heated above
a temperature specific to that TIM.
• Material Thermal Conductivity — The thermal conductivity of the interface material.
While the wetting and thermal conductivity are material dependent characteristics, the bond line
thickness is primarily controlled by the interfacial pressure between the heat sink and package (as well
as the TIM malleability). Typically, higher interfacial pressure leads to lower thermal conductivity as
demonstrated (for example only) in the plot the follows.
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