Intel Pentium 4 Processor In the 423-pin Package Thermal Design Guidelines

Pentium® 4 processor in the 423-pin package Thermal Design Guidelines

5.6.2 Direction

For passive cooling solutions, if the fan(s) is (are) not moving air through the heat sink, then little cooling can occur

and the processor may operate above the specified temperature. Two possibilities exist for blowing air through the

heat sink of a Pentium® 4 processor. Air can be blown horizontally, parallel to the baseboard, which blows the air

through the length of the heat sink. Alternatively the air stream can be blown vertically, perpendicular to the

baseboard, or down into the heat sink. This will depend on the layout of other components on the board and/or

within the chassis. Preferably the intake fan will blow through the heat sink lengthwise. In this case, it may be

possible for the heat sink fins to be shorter (z – axis). Both of these factors are considerations when laying out

components on the board and in the chassis.

The direction of the chassis airflow can be modified with baffles or ducts to direct the airflow toward the processor.

This will increase the local flow through the processor heat sink and may eliminate the need for a second, larger, or

higher speed fan. Baffles and ducts can also provide air to the heat sink without the preheating caused by other

system components

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 or axial fan using

ducting might direct more air through the heat sink than a large axial fan blowing non-directed air toward the heat

sink. The following provide some guidelines for size and quantity of the fan(s).

The system fan should be a minimum of 80 mm (3.150") square, with a minimum airflow of approximately

200 LFM (linear feet per minute). Ideally two (2) fans should be used. The intake air fan would blow cool air

directly toward the processor and heat sink assembly, while a second fan, possibly in the power supply would

exhaust the hot air out of the system.

5.6.4 Venting

Intake venting should be placed at the front (user side) of the system to avoid any re-circulation that can occur from

the rear of a system with little wall clearance. Location should be selected with consideration for cooling of

processor and peripherals (drives and add-in cards). Intake venting directly in front of the intake fan is the most

optimal location. The ideal design will provide airflow directly through the processor heat sink.

5.6.4.1 Placement

Exhaust venting in conjunction with the power supply exhaust fan is usually sufficient for smaller systems.

However, depending on the number, location and types of add-in cards, exhaust venting may be necessary near the

adapter cards. This should be modeled or prototyped for the optimum thermal potential. Hence, a system should be

modeled for the worst case; i.e. all expansion slots should be occupied with add-in options.

5.6.4.2 Area and/or Size

The area and/or size of the intake vents should consider the size and shape of the fan(s). Adequate air volume must

be obtained and thus will require adequate sized vents. Intake vents should be located in front of the intake fan(s)

and adjacent to the drive bays. Venting should be approximately 50% to 60% open in the EMI (Electro-Magnetic

Interference) containment area. Outside the EMI (Electro-magnetic Interference) containment area, the open

percentage can be greater if needed for aesthetic appeal (i.e., bezel/cosmetics). Caution should be exercised that

venting is not excessive or poorly placed which can cause re-circulation of warm exhaust air.

5.6.4.3 Vent Shape

Round, staggered pattern openings are best for EMI containment, acoustics and airflow balance.