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

Thermal Requirements
R
Intel
®
Pentium
®
4 on 90 nm Process Thermal Design Guide 19
The case-to-local ambient thermal characterization parameter value (Ψ
CA
) is used as a measure of
the thermal performance of the overall thermal solution that is attached to the processor package.
It is defined by the following equation, and measured in units of °C/W:
Equation 1
Ψ
CA
= (T
C
– T
A
) / P
D
Where:
Ψ
CA
= Case-to-local ambient thermal characterization parameter (°C/W)
T
C
= Processor case temperature (°C)
T
A
= Local ambient temperature in chassis at processor (°C)
P
D
= Processor total package power dissipation (W)
The case-to-local ambient thermal characterization parameter of the processor, Ψ
CA
, is comprised
of Ψ
CS
, the thermal interface material thermal characterization parameter, and of Ψ
SA
, the sink-to-
local ambient thermal characterization parameter:
Equation 2
Ψ
CA
= Ψ
CS
+ Ψ
SA
Where:
Ψ
CS
= Thermal characterization parameter of the thermal interface material (°C/W)
Ψ
SA
= Thermal characterization parameter from heatsink-to-local ambient (°C/W)
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 illustrates the combination of the different thermal characterization parameters.