Table of Contents
Advertisement
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
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
, and the local air velocity over the surface. The higher the air velocity over the
LA
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.
2.4.2
Thermal Interface Material
TIM application between the processor IHS and the heatsink base is generally required
to improve thermal conduction from the IHS to the heatsink. Many thermal interface
materials can be pre-applied to the heatsink base prior to shipment from the heatsink
supplier and allow direct heatsink attach, without the need for a separate TIM dispense
or attach process in the final assembly factory.
All thermal interface materials should be sized and positioned on the heatsink base in a
way that ensures the entire processor IHS area is covered. It is important to
compensate for heatsink-to-processor attach positional alignment when selecting the
proper TIM size.
When pre-applied material is used, it is recommended to have a protective application
tape over it. This tape must be removed prior to heatsink installation.
34
Dual-Core Intel® Xeon® Processor 5100 Series Thermal/Mechanical Design Guide
Thermal/Mechanical Reference Design
Section 2.4.2
for further information
Advertisement
Table of Contents
