Intel Pentium 4 Processor on 90 nm Process Thermal and Mechanical Design Guidelines

Thermal Requirements
R
20 Intel
®
Pentium
®
4 on 90 nm Process Thermal Design Guide
Figure 3. Processor Thermal Characterization Parameter Relationships
HEATSINK
IHS
TIM
PROCESSOR
T
S
T
C
T
A
SOCKET
Ψ
SA
Ψ
CS
Ψ
CA
HEATSINK
IHS
TIM
PROCESSOR
T
S
T
C
T
A
SOCKET
Ψ
SA
Ψ
CS
Ψ
CA
3.2.3.1 Example
The cooling performance, Ψ
CA,
is then defined using the principle of thermal characterization
parameter described above:
• Define a target case temperature T
C-MAX,F
and corresponding thermal design power TDP
F
at a
target frequency, F, given in the processor datasheet.
• Define a target local ambient temperature at the processor, T
A
.
Since the processor thermal specifications (T
C-MAX
and TDP) can vary with the processor
frequency and power load, it may be important to identify the worse 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 and power loads.
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 75 W and the case temperature specification is 65 °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 from above:
Equation 3
Ψ
CA
= (T
C,F
– T
A
) / TDP
F
= (65 – 38) / 75 = 0.36 °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
≤ 0.05 °C/W,
solving for Equation 2 from above, the performance of the heatsink would be:
Equation 4
Ψ
SA
= Ψ
CA
− Ψ
CS
= 0.36 − 0.05 = 0.31 °C/W