Intel 200 ユーザーズマニュアル

Thermal and Mechanical Design Guidelines 

 27 

This section discusses guidelines for testing thermal solutions, including measuring 

processor temperatures.  In all cases, the thermal engineer must measure power 

dissipation and temperature to validate a thermal solution.  To define the performance 

of a thermal solution the “thermal characterization parameter”, Ψ (“psi”) will be used. 

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 situations (same heat source and local ambient conditions).  The 

thermal characterization parameter is calculated using total package power.  

Note:  Heat transfer is a three-dimensional phenomenon that can rarely be accurately and 

easily modeled by a single resistance parameter like Ψ. 

The junction-to-local ambient thermal characterization parameter value (Ψ

JA

) is used 

as a 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   

Ψ

JA

 = (T

J

 – T

A

) / P

D

 

Where: 

Ψ

JA

 

=  Junction-to-local ambient thermal characterization parameter (°C/W) 

T

J

 

=  Processor junction temperature (°C) 

T

A

 

=  Local ambient temperature in chassis at processor (°C) 

P

D

 

=  Processor total power dissipation (W) (assumes all power dissipates 

through the processor die)