Processor Thermal Characterization Parameter Relationships - Intel 5100 Series Instruction Manual

Thermal/Mechanical Reference Design
2.3.2 Processor Thermal Characterization Parameter
Relationships
The idea of a "thermal characterization parameter", Ψ (psi), is a convenient way to
characterize the performance needed for the thermal solution and to compare thermal
solutions in identical conditions (heating source, local ambient conditions). A thermal
characterization parameter is convenient in that it is calculated using total package
power, whereas actual thermal resistance, θ (theta), is calculated using actual power
dissipated between two points. Measuring actual power dissipated into the heatsink is
difficult, since some of the power is dissipated via heat transfer into the socket and
board. Be aware, however, of the limitations of lumped parameters such as Ψ 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 case-to-local ambient thermal characterization parameter value (Ψ
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 2-3.Ψ = (T
CA
Where:
Ψ
CA
T
CASE
T
LA
TDP = TDP dissipation (W) (assumes all power dissipates through the integrated
The case-to-local ambient thermal characterization parameter of the processor, Ψ
comprised of Ψ
local ambient thermal characterization parameter:
Equation 2-4.Ψ = Ψ
CA CS
Where:
=Thermal characterization parameter of the TIM (°C/W).
Ψ
CS
=Thermal characterization parameter from heatsink-to-local ambient (°C/W).
Ψ
SA
is strongly dependent on the thermal conductivity and thickness of the TIM
Ψ
CS
between the heatsink and IHS.
is a measure of the thermal characterization parameter from the bottom of the
Ψ
SA
heatsink to the local ambient air. Ψ
conductivity, and geometry. It is also strongly dependent on the air velocity through
the fins of the heatsink.
Dual-Core Intel® Xeon® Processor 5100 Series Thermal/Mechanical Design Guide
- T ) / TDP
CASE LA
= Case-to-local ambient thermal characterization parameter (°C/W).
= Processor case temperature (°C).
= Local ambient temperature in chassis at processor (°C).
heat spreader (IHS)).
, the TIM thermal characterization parameter, and of Ψ
CS
+ Ψ
SA
is dependent on the heatsink material, thermal
SA
) is used as a
CA
, is
CA
, the sink-to-
SA
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