Intel Xeon E5405 BX80574E5405 User Manual

Quad-Core Intel® Xeon® Processor 5400 Series TMDG

35

The case-to-local ambient thermal characterization parameter of the processor, Ψ

CA

, is 

comprised of Ψ

CS

, the TIM thermal characterization parameter, and of Ψ

SA

, the sink-to-

local ambient thermal characterization parameter:

Equation 2-4.Ψ

= Ψ

 + Ψ

Where:

Ψ

CS

= Thermal characterization parameter of the TIM (°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.

 illustrates the combination of the different thermal characterization 

parameters.

The cooling performance, Ψ

CA,

 is then defined using the principle of thermal 

characterization parameter described above:

• Define a target case temperature T

CASE_MAX

 and corresponding TDP, given in the 

processor datasheet.

• Define a target local ambient temperature at the processor, T

LA

. 

The following provides an illustration of how one might determine the appropriate 
performance targets. The example power and temperature numbers used here are not 
related to any Intel processor thermal specifications, and are for illustrative purposes 
only.