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

Pentium® 4 Processor in the 423-pin Package Thermal Design Guidelines
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6 ALTERNATIVE COOLING SOLUTIONS
In addition to passive heat sink, fan heat sinks and system fans, other solutions exist for cooling integrated circuit
devices. For example, ducted blowers, heat pipes and liquid cooling are all capable of dissipating additional heat.
Due to their varying attributes, each of these solutions may be appropriate for a particular system implementation.
More information on this topic can be located on Intel's web site at http://developer.intel.com/.
6.1 Ducting
Ducts can be designed to isolate the processor from the effects of system heating (such as add-in cards), and to
maximize the processor cooling temperature budget. Typical temperature rise from external ambient to the local
ambient near the processor can be greater than 10
o
C. Air provided by a fan or blower can be channeled to the
processor and heat sink with little or no rise from the external ambient temperature.
6.1.1 Ducting Placement
When ducting is to be used, it should direct the airflow evenly from the fan through the length of the heat sink. This
should be accomplished, if possible, with smooth, gradual turns, as this will enhance the airflow characteristics.
Sharp turns in ducting should be avoided as they increase friction, drag, and pressure drop and will greatly reduce
the volume of air reaching the processor heat sink.
6.2 System Components
6.2.1 Placement
Peripherals such as CD-ROMs, floppy drives, hard drives, VR/M (voltage regulators/modules), etc. can be placed to
take advantage of a fan's movement of ambient air (by placing them near intake or exhaust fans or venting). Some
add-in cards often have a low tolerance for temperature rise. These components should be placed near additional
venting if they are downstream of the processor to minimize an increase in their ambient temperature.
6.2.2 Power
Some types of drives, such as floppy drives, do not dissipate much heat, while others (e.g. read/write CD-ROM
drives, SCSI drives) dissipate a great deal of heat. These hotter components should be placed near fans and/or
venting whenever possible. The same can be said for some types of add-in cards. Some PCI cards are very low
wattage (approximately 5W) while others can be as high as 25W, per the PCI specification. AGP graphics devices
can dissipate up to 25W per the AGP revision 2.0 specifications while AGP Pro50 devices dissipate 25-50W and
AGP Pro110 devices dissipate 50-110W per AGP Pro revision 1.1a specifications. Great care should be taken to
ensure that these cards have sufficient cooling, while not adversely affecting the processor cooling.
6.2.3 Voltage Regulation Module (VRM) Considerations
Voltage regulation module (VRM) designs must also be considered in system cooling solutions. Because proper
power delivery to the processor demands that the VRM be placed very close to the processors, local ambient
temperature for the VRM may be affected by the heating of the nearby processors. Thermal modeling of the system
should therefore include the VRM in the simulation.
7 THERMAL METROLOGY
The following sections will discuss the techniques for testing thermal solutions. It should be noted that determining
if a processor is sufficiently cooled is not as simple as it may seem. Carefully read the following instructions and
interpretation steps to validate your cooling solution.