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®
®
Intel
Pentium
III Processor in the FC-PGA2 Package Thermal Design Guidelines
5.6.1.
Placement
Proper placement of the fans can ensure that the processor is being properly cooled. Because of the
difficulty in building, measuring, and modifying a mechanical assembly for thermal evaluation, models
are typically developed and used to simulate a proposed design for thermal effectiveness, and to
determine the optimum location for fans and vents within a chassis. Investments for prototype
assemblies can then be made to verify that the system components and processor thermal specifications
are met.
5.6.2.
Fan Direction
If the fan(s) are not moving air across the processor heatsink, cooling will not occur. This may cause the
processor to operate well above the recommended specification values. Two possibilities exist for
blowing air across a passive heatsink. Air can be blown down vertically or horizontally across the
heatsink. This may depend on the layout of other components on the board and/or within the chassis.
The intake fan should blow through a passive heatsink parallel to the fins if possible. Both of these
factors are considerations when laying out components on the board and in the chassis.
The direction of the airflow can be modified with baffles or ducts to direct the airflow over the processor.
This will increase the local flow over the processor and may eliminate the need for a second fan, a larger
fan, or a higher speed fan. For an actively cooled heatsink, the system airflow direction may not be as
critical for proper thermal performance, but it will be important to manage warm air re-circulation.
5.6.3.
Size and Quantity
It does not necessarily hold true that the larger the fan the more air it blows. A small blower using
ducting might direct more air over the heatsink than a large fan blowing non-directed air over the
heatsink.
5.6.4.
Venting
Intake venting should be placed at the front (user side) of the system. They should be located to optimize
cooling of processor and peripherals (drives and add-in cards). A good starting point would be the lower
50% of the front panel (bezel). Intake vents directly in front of the intake fan, is the optimal location.
The ideal design will provide airflow directly over the processor heatsink.
5.6.4.1.
Placement
In most cases, an exhaust fan and vent located at the power supply is sufficient. However, depending on
the number, location, and types of add-in cards, exhaust venting may be necessary near the cards. This
should be modeled or prototyped for the optimum thermal potential. A system should be modeled for the
worst case, i.e., all expansion slots should be occupied with typical add-in options.
5.6.4.2.
Area and Size
The area and size of the intake vents should be designed with the size and shape of the fan(s) in mind.
Adequate air volume requires appropriately sized vents. Intake vents should be located in front of the
intake fan(s) and adjacent to the drive bays. Vents should be approximately 50% to 60% open in the
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