Intel Pentium 4 Processor In the 423-pin Package Thermal Design Guidelines

Pentium® 4 processor in the 423-pin package Thermal Design Guidelines
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7.1 Thermal Metrology for Pentium® 4 processors
7.1.1 Thermal Resistance
The thermal resistance value from case-to-local ambient (Θ
CA
) is used as a measure of the cooling solution's thermal
performance. Thermal resistance is measured in units of °C/W. The thermal resistance of the case-to-local ambient,
Θ
CA
, is comprised of the Θ
TIM
thermal interface material thermal resistance and the sink-to-local ambient thermal
resistance (Θ
SA
) Figure 6. This value Θ
TIM
,
is strongly dependent on the thermal conductivity and thickness of the
TIM between the heat sink and surface of the processor.
Θ
SA
is a measure of the thermal resistance from the bottom of the cooling solution to the local ambient air. Θ
SA
is
dependent on the heat sink’s material, thermal conductivity and geometry, and is strongly dependent on the air
velocity through the fins of the heat sink.
Θ
CA
Θ
SA
T
LA
TIM
Heatsink
Processor
000971
Figure 6. Thermal Resistance Relationships
The thermal parameters are related by the following equations:
Equation 1. Case to Ambient Thermal Resistance:
Θ
CA
= (T
CASE
- T
LA
) / P
D
Equation 2. Case to Ambient Thermal Resistance:
Θ
CA
= Θ
TIM
+Θ
SA
Where:
Θ
CA
= Thermal resistance from case-to-local ambient (°C/W)
T
CASE
= Processor case temperature (°C)
T
LA
= Local ambient temperature in chassis around processor (°C)
P
D
= Processor power dissipation (W) (assume all power goes to the case)
Θ
TIM
= Thermal resistance of the thermal interface material (°C/W)
Θ
SA
= Thermal resistance from heat sink-to-local ambient (°C/W)