Intel Celeron D, Thermal Design Manual

Page: 19 / 64

Intel
®
Celeron
®
D Processor in the 775-Land LGA Package Thermal Design Guide 19
Order #
303730
Thermal Metrology
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 4 illustrates the combination of the different thermal characterization parameters.
3.1.1 Example
The cooling performance,
Ψ
CA,
is defined using the thermal characterization parameter described
in the previous section:
•
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 such that a given heatsink can cover a given range of processor frequencies.
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 Intel
processor thermal specifications, and are for illustrative purposes only.
Assume the datasheet TDP is 100 W and the maximum case temperature from the thermal profile
for 100W is 67
° C. Assume as well that the system airflow has been designed such that the local
ambient temperature is 38
°
C. Then the following could be calculated using Equation 1 :
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
Figure 4. 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