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Intel
Pentium
III Processor in the FC-PGA2 Package Thermal Design Guidelines
5.2.
Recommended Fan Performance and Limitations
For active thermal solutions, the fan must often demonstrate a functional lifetime of 40,000 hours or
greater. In addition, the fan should demonstrate performance to the reliability criteria outlined in the FC-
PGA2 Package Thermal/Mechanical Solution Functional Specifications.
5.3.
Bypass
Bypass is the distance around a passive heatsink where air may travel without passing through the fins of
the heatsink. A heatsink will have infinite bypass if it is sitting in free space, while a heatsink that has a
duct, or other devices surrounding it which are 0.2 in (5.1mm) away from the outer edges of the heatsink,
has a bypass of 0.2 in (5.1mm). A smaller bypass forces more air to pass through the fins of the heatsink,
instead of around the heatsink. This is especially important as the heatsink fin density increases. The
higher the fin density, the more resistance the heatsink poses to the air and the more likely the air will
travel around the heatsink instead of through it unless the bypass is small. Air traveling around the
heatsink will have no affect on cooling the processor.
5.4.
Heatsink Solutions and Keep-in Areas
One method used to improve thermal performance is to increase the surface area of the device by
attaching a metallic heatsink. To maximize the heat transfer, the thermal resistance from the heatsink to
the air can be reduced by maximizing the airflow through the heatsink fins as well as by maximizing the
surface area of the heatsink itself. Although there have been many advancements in fin density and
geometries that allow for a better performing heatsink, an active or more advanced thermal solution may
be needed. Intel is enabling reference active and passive heatsinks for FC-PGA2 packaged processors.
Please see the FC-PGA2 Package Thermal/Mechanical Solution Functional Specifications for further
details.
5.5.
Thermal Interface Management
To optimize the heatsink design for FC-PGA2 packaged processors, it is important to understand the
impact of factors related to the interface between the processor and the heatsink base. Specifically, the
interface material bond line thickness, area, and bulk thermal conductivity should be managed to realize
the most effective thermal solution.
Thermal interface material must be applied between the processor IHS and the heatsink to improve
thermal conduction from the IHS to the heatsink. Thermal interface material also serves as a mechanical
load element during mechanical stress testing (i.e. mechanical shock). 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 thermal interface material dispense or attach process in
the final assembly factory.
All thermal interface materials must be sized and positioned on the heatsink base in a way that ensures
the entire processor IHS area is covered. It will be important to compensate for heatsink-to-processor
attach positional alignment when selecting the proper thermal interface material size.
If a pre-applied thermal interface material is specified, it may have a protective application tape. This
tape must be removed prior to heatsink attach.
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249660-001
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