Intel Xeon processor LV Thermal Design Guide

Thermal Solution Requirements
Dual-Core Intel
®
Xeon
®
processor LV and ULV
Thermal Design Guide August 2006
20 Reference Number: 311374-002
5.0 Thermal Solution Requirements
5.1 Characterizing the Thermal Solution Requirement
The idea of a “thermal characterization parameter” Ψ (pronounced Psi), is a convenient
way to characterize the performance needed for the thermal solution and to compare
thermal solutions in identical situations (i.e., heating source, local ambient conditions,
etc.). The thermal characterization parameter 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 package and
board.
The junction-to-local ambient thermal characterization parameter (Ψ
JA
) is used as a
measure of the thermal performance of the overall thermal solution. It is defined by
Equation 1 and expressed in units of °C/W.
Equation 1. Junction-to-Local Ambient Thermal Characterization Parameter (Ψ
JA
)
Where:
Ψ
JA
= Junction-to-local ambient thermal characterization parameter (°C/W)
T
JUNCTION MAX
= Maximum allowed device temperature (°C)
T
LA
= Local ambient temperature near the device (°C)
TDP = Thermal Design Power (W), assumes all power dissipates through the top
surface of the device.
The junction-to-local ambient thermal characterization parameter, Ψ
JA
, is comprised of
Ψ
JS
, which includes the thermal interface material thermal characterization parameter,
and of Ψ
SA
, the sink-to-local ambient thermal characterization parameter:
Equation 2. Junction-to-Local Ambient Thermal Characterization Parameter (Ψ
JA
)
Where:
Ψ
JS
(Ψ
TIM
) = Thermal characterization parameter from the junction-to-sink, this also
includes the resistance of the thermal interface material (°C/W)
Ψ
SA
= Thermal characterization parameter from heatsink-to-local ambient (°C/W)
Ψ
TIM
is strongly dependent on the thermal conductivity and thickness of the TIM
between the heatsink and device package.
T
D
P
TT
LAJ
JA
−
=Ψ
S
A
JSJA
Ψ+Ψ=Ψ