Intel CORETM 2 DUO MOBILE 320028-001 - Manual (Page 15)

Core™ 2 Duo Mobile Processors—Thermal Solution Requirements
Intel® Core™ 2 Duo Mobile Processors on 45-nm process-Thermal Design Guide
TDG June 2008
15 Order Number: 320028-001
5.0 Thermal Solution Requirements
5.1 Thermal Solution Characterization
The thermal characterization parameter, Ψ (“psi”), is used to characterize thermal solution
performance, as well as compare thermal solutions in identical situations (i.e., heating source, local
ambient conditions, etc.). It is defined by the following equation:
Ψ
JA
= Junction-to-local ambient thermal characterization parameter (°C/W)
T
JUNCTION MAX
= Maximum allowed device temperature (°C)
T
A
= Local ambient temperature near the device (°C) (see Section 7.0, “Thermal Metrology” for
measurement guidelines)
TDP = Thermal Design Power (W)
The thermal characterization parameter assumes that all package power dissipation is through the
thermal solution (heatsink), and is equal to TDP. A small percentage of the die power (< 5%) is
dissipated through the package/socket/motherboard stack to the environment, and should not be
considered to be a means of thermal control.
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:
Where:
Ψ
JS
= Thermal characterization parameter from junction-to-sink, this also includes thermal resistance
of the thermal interface material (Ψ
TIM
) (°C/W).
Ψ
SA
= Thermal characterization parameter from sink-to-local ambient (°C/W)
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 5 illustrates the
combination of the different thermal characterization parameters.
Equation 1. Junction-to-Local Ambient Thermal Characterization Parameter (Ψ
JA
)
Equation 2. Junction-to-Local Ambient Thermal Characterization Parameter
TDP
T T
A J
JA
−
= Ψ
Ψ
JA
= Ψ
JS
+ Ψ
SA