Intel Pentium 4 Processor with 512-KB L2 Cache on 0.13 Micron Process Thermal Design Guidelines

Thermal Specifications
R
Intel
®
Pentium
®
4 Processor Thermal Design Guide 19
3.3 Thermal Metrology for the Intel
®
Pentium
®
4
Processor with 512-KB L2 Cache on 0.13 Micron
Process
3.3.1 Processor Cooling Solution Performance Assessment
This section discusses guidelines for testing thermal solutions, including measuring processor
temperatures. In all cases, power dissipation and temperature measurements must be made to
validate a cooling solution.
Thermal performance of a processor heatsink in a chassis should be assessed using a thermal test
vehicle (TTV) provided by Intel (refer to Section 3.3.4). A TTV is a well-characterized thermal
tool; using real parts introduces other factors that can impact test results. In particular, the power
level from real processors varies significantly. This is due to part-to-part variances in the
manufacturing process. The TTV provides consistent power and power density for thermal
solution characterization and results can be easily translated to real processor performance.
Accurate measurement of the power dissipated by a real processor is beyond the scope of this
document.
Once the thermal solution and chassis are designed and validated with the TTV, it is recommended
to verify functionality of the thermal solution on real processors and on fully integrated systems
(see Section 3.4).
3.3.2 Local Ambient Temperature Measurement Guidelines
The local ambient temperature T
A
is the temperature of the ambient air surrounding the processor.
For a passive heatsink, T
A
is defined as the heatsink approach air temperature; for an actively
cooled heatsink, it is the temperature of inlet air to the active cooling fan.
It is worthwhile to determine the local ambient temperature in the chassis around the processor to
understand the effect it may have on the case temperature.
T
A
is best measured by averaging temperature measurements at multiple locations in the heatsink
inlet airflow. This method helps reduce error and eliminate minor spatial variations in temperature.
The following guidelines are meant to enable accurate determination of the localized air
temperature around the processor during system thermal testing.
For active heatsinks, it is important to avoid taking measurement in the dead flow zone that
usually develops above the fan hub. Measurements should be taken at four different locations
uniformly placed at the center of the annulus formed by the fan hub and the fan housing to
evaluate the uniformity of the air temperature at the fan inlet. The thermocouples should be placed
approximately 2.54 mm to 7.62 mm (0.1 to 0.3 inch) above the fan hub vertically, and halfway
between the fan hub and the fan housing horizontally as shown in Figure 3. Testing in an open
bench environment to characterize an active heatsink can be useful, and usually ensures more
uniform temperatures at the fan inlet. However, additional tests that include a barrier above the
test motherboard surface can help evaluate the potential impact of the chassis. This barrier is
typically clear Plexiglas*, extending at least 4 inches in all directions beyond the edge of the
thermal solution. Typical distance from the motherboard to the barrier is 81mm [3.2in]. For even
more realistic airflow, the motherboard should be fully populated with significant elements like