Intel 5400 Series - Manual (Page 37)

Quad-Core Intel® Xeon® Processor 5400 Series TMDG 37
Thermal/Mechanical Reference Design
To develop a reliable, cost-effective thermal solution, thermal characterization and
simulation should be carried out at the entire system level, accounting for the thermal
requirements of each component. In addition, acoustic noise constraints may limit the
size, number, placement, and types of fans that can be used in a particular design.
2.5 Thermal/Mechanical Reference Design
Considerations
2.5.1 Heatsink Solutions
2.5.1.1 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 strict. Thermal interface material (TIM) is used to fill
in the gap between the IHS and the bottom surface of the heatsink, and thereby
improves the overall performance of the thermal stackup (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 load applied to it. Refer to
Section 2.5.2 for further information
on the TIM 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
LA
, and the local air velocity over the surface. The higher the air velocity over the
surface, the resulting cooling is more efficient. 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 the
fin faces and the heatsink base.
An active heatsink typically incorporates a fan that helps manage the airflow through
the heatsink.
Passive heatsink solutions require in-depth knowledge of the airflow in the chassis.
Typically, passive heatsinks see slower air speed. Therefore, these heatsinks are
typically larger (and heavier) than active heatsinks due to the increase in fin surface
required to meet a required performance. As the heatsink fin density (the number of
fins in a given cross-section) increases, the resistance to the airflow increases: it is
more likely that the air will travel around the heatsink instead of through it, unless air
bypass is carefully managed. Using air-ducting techniques to manage bypass area is an
effective method for maximizing airflow through the heatsink fins.