18
Intel
®
Celeron
®
D Processor in the 775-Land LGA Package
Thermal Design Guide
Order #303730
Thermal Metrology
3.0
Thermal Metrology
This chapter 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.
3.1
Characterizing Cooling Performance Requirements
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 (heat source, local ambient conditions). The thermal characterization parameter is
calculated using total package power. Note that heat transfer is a three-dimensional phenomenon
that can rarely be accurately and easily modeled by a single resistance parameter like
Ψ
.
The case-to-local ambient thermal characterization parameter value (
Ψ
CA
) 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 1.
Ψ
CA
= (T
C
- T
A
) / P
D
Where:
Ψ
CA
= Case-to-local ambient thermal characterization parameter (°C/W)
T
C
= Processor case 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 IHS)
The case-to-local ambient thermal characterization parameter of the processor,
Ψ
CA
, is composed
of
Ψ
CS
, the thermal interface material thermal characterization parameter, and of
Ψ
SA
, the
sink-to-local ambient thermal characterization parameter:
Equation 2.
Ψ
CA
=
Ψ
CS
+
Ψ
SA
Where:
Ψ
CS
=
Thermal characterization parameter of the thermal interface material (°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.
