Intel QX68000 Core 2 Extreme, Design Manual

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Processor Thermal/Mechanical Information
Thermal and Mechanical Design Guidelines 19
This is achieved in part by using the Ψ
CA
vs. RPM and RPM vs. Acoustics (dBA)
performance curves from the Intel enabled thermal solution. A thermal solution
designed to meet the thermal profile would be expected to provide similar acoustic
performance of different parts with potentially different T
CONTROL
values.
The value for T
CONTROL
is calculated by the system BIOS based on values read from a
factory configured processor register. The result can be used to program a fan speed
control component. See the processor datasheet for further details on reading the
register and calculating T
CONTROL
.
See Chapter 6 Intel
®
Quiet System Technology (Intel
®
QST) for details on
implementing a design using T
CONTROL
and the Thermal Profile.
2.3 Heatsink Design Considerations
To remove the heat from the processor, three basic parameters should be considered:
• The area of the surface on which the heat transfer takes place. Without
any enhancements, this is the surface of the processor package IHS. One method
used to improve thermal performance is by attaching a heatsink to the IHS. A
heatsink can increase the effective heat transfer surface area by conducting heat
out of the IHS and into the surrounding air through fins attached to the heatsink
base.
• The conduction path from the heat source to the heatsink fins. Providing a
direct conduction path from the heat source to the heatsink fins and selecting
materials with higher thermal conductivity typically improves heatsink
performance. The length, thickness, and conductivity of the conduction path from
the heat source to the fins directly impact the thermal performance of the
heatsink. In particular, the quality of the contact between the package IHS and
the heatsink base has a higher impact on the overall thermal solution performance
as processor cooling requirements become stricter. Thermal interface material
(TIM) is used to fill in the gap between the IHS and the bottom surface of the
heatsink, and thereby improve the overall performance of the stack-up (IHS-TIM-
Heatsink). With extremely poor heatsink interface flatness or roughness, TIM may
not adequately fill the gap. The TIM thermal performance depends on its thermal
conductivity as well as the pressure applied to it. Refer to Section
2.3.3 and
Appendix C for further information on TIM and on bond line management between
the IHS and the heatsink base.
• The heat transfer conditions on the surface on which heat transfer takes
place. Convective heat transfer occurs between the airflow and the surface
exposed to the flow. It is characterized by the local ambient temperature of the
air, T
A
, and the local air velocity over the surface. The higher the air velocity over
the surface, and the cooler the air, the more efficient is the resulting cooling. The
nature of the airflow can also enhance heat transfer via convection. Turbulent
flow can provide improvement over laminar flow. In the case of a heatsink, the
surface exposed to the flow includes in particular the fin faces and the heatsink
base.
Liquid Cooling Technology typically incorporates a fan, an integrated pump with
cold plate and an air radiator type heat exchanger. The design takes advantage of a
pump to provide a uniform liquid-flow across the cold plate taking away the heat then
go to the exchanger. Finally, a fan manages the airflow through the exchanger.
Active heatsinks typically incorporate a fan that helps manage the airflow through
the heatsink.