Intel740™ Graphics Accelerator Thermal Design Considerations
18 Application Note 653
4.3.1 Bond Line Management
The gap between the mold-cap and the heat sink base will impact heat-sink solution performance.
The larger the gap between the two surfaces, the greater the thermal resistance. The thickness of
the gap is determined by the flatness of both the heat sink base and the mold-cap, plus the thickness
of the thermal interface material (e.g., PSA, thermal grease, epoxy) used between these two
surfaces.
The Intel740 graphics accelerator mold cap planarity is specified as 0.006 inches maximum (see
the Intel740™ Graphics Accelerator Datasheet, order number 290618, for package drawing).
4.3.2 Interface Material Performance
Two factors impact the performance of the interface material between the thermal plate and the
heat sink base:
• Thermal resistance of the material
• Wetting/filling characteristics of the material
Thermal resistance is a description of the ability of the thermal interface material to transfer heat
from one surface to another. The higher the thermal resistance, the less efficient an interface is at
transferring heat. The thermal resistance of the interface material has a significant impact on the
thermal performance of the overall thermal solution. The higher the thermal resistance, the higher
the temperature drop across the interface and the more efficient the thermal solution must be.
The wetting/filling of the thermal interface material is its ability to fill the gap between the case and
the heat-sink. Since air is an extremely poor thermal conductor, the more completely the interface
material fills the gaps, the lower the temperature drop across the interface.
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