Thermal Metrology
R
Thermal/Mechanical Design Guide 27
has been designed such that the local ambient temperature is 38 °C. Then the following could be
calculated using Equation 1 from above:
Ψ
CA
= (T
C
– T
A
) / TDP = (67 – 38) / 100 = 0.29 °C/W
To determine the required heatsink performance, a heatsink solution provider would need to
determine Ψ
CS
performance for the selected TIM and mechanical load configuration. If the
heatsink solution were designed to work with a TIM material performing at Ψ
CS
≤ 0.10 °C/W,
solving for Equation 2 from above, the performance of the heatsink would be:
Ψ
SA
= Ψ
CA
− Ψ
CS
= 0.29 − 0.10 = 0.19 °C/W
3.2 Processor Thermal Solution Performance
Assessment
Thermal performance of a heatsink should be assessed using a thermal test vehicle (TTV)
provided by Intel. The TTV is a stable heat source from which the user can take accurate power
measurements, whereas actual processors can introduce additional factors that can impact test
results. In particular, the power level from actual processors varies significantly due to 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.
Once the thermal solution is designed and validated, it is strongly recommended to verify
functionality of the thermal solution on real processors and on fully integrated systems.
Contact your Intel field sales representative for further information on TTV or regarding accurate
measurement of the power dissipated by an actual processor.
3.3 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 approaches 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 and hub spokes. 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
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