Intel Pentium 4 Processor with 512-KB L2 Cache on 0.13 Micron Process Thermal Design Guidelines

Thermal Specifications
R
Intel
®
Pentium
®
4 Processor Thermal Design Guide 17
3.2.2.3 Characterizing Cooling Performance Requirements
The notion of a “thermal characterization parameter” is convenient to characterize the
performance needed for the cooling solution and to compare cooling solutions in identical
situations. Be aware, however, of its limitation when it comes to a real design. Heat transfer is a
three-dimensional phenomenon that can rarely be accurately and easily modeled by lump values.
The thermal characterization parameter value from case-to-local ambient (Ψ
CA
) is used as a
measure of the thermal performance of the overall cooling 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
) / TPD
Where:
Ψ
CA
= Thermal characterization parameter from case-to-local ambient (°C/W)
T
C
= Processor case temperature (°C)
T
A
= Local ambient temperature in chassis around processor (°C)
TPD = Thermal design power (W) (assume all power goes through the IHS)
The thermal characterization parameter of the processor case-to-local ambient, 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 heat sink’s material, thermal conductivity, and
geometry. It is also strongly dependent on the air velocity through the fins of the heatsink.