Thermal Metrology
28 Thermal and Mechanical Design Guidelines
Ψ
CS
is strongly dependent on the thermal conductivity and thickness of the TIM
between the heatsink and IHS.
Ψ
SA
is a measure of the thermal characterization parameter from the bottom of the
heatsink to the local ambient air. Ψ
SA
is dependent on the heatsink material, thermal
conductivity, and geometry. It is also strongly dependent on the air velocity through
the fins of the heatsink.
Figure 3-1 illustrates the combination of the different thermal characterization
parameters.
Figure
3-1. Processor Thermal Characterization Parameter Relationships
TIM
T
S
T
A
Ψ
CA
LGA775 Socket
Processor
IHS
System Board
T
C
Heatsink
TIM
T
S
T
A
Ψ
CA
LGA775 Socket
Processor
IHS
System Board
T
C
Heatsink
3.1.1 Example
The cooling performance, Ψ
CA,
is then defined using the principle of thermal
characterization parameter described above:
• The case temperature T
C-MAX
and thermal design power TDP given in the processor
datasheet.
• Define a target local ambient temperature at the processor, T
A
.
Since the processor thermal profile applies to all processor frequencies, it is important
to identify the worst case (lowest Ψ
CA
) for a targeted chassis characterized by T
A
to
establish a design strategy.
The following provides an illustration of how one might determine the appropriate
performance targets. The example power and temperature numbers used here are not
related to any specific Intel processor thermal specifications, and are for illustrative
purposes only.
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