Intel Pentium 4 Processor in the 478-Pin Package Thermal Design Guidelines

Intel
®
Pentium
®
4 Processor in the 478-Pin Package Thermal Design Guidelines
R
16 Design Guide
Θ
CA
= (T
C
- T
A
) / P
D
(Equation 1)
Where:
Θ
CA
= Thermal resistance from case-to-local ambient (°C/W)
T
C
= Processor case temperature (°C)
T
A
= Local ambient temperature in chassis around processor (°C)
P
D
= Processor power dissipation (W) (assume all power goes through the IHS)
The thermal resistance of the processor case-to-local ambient, Θ
CA
, is comprised of Θ
CS
, the
thermal interface material thermal resistance, and of Θ
SA
, the sink-to-local ambient thermal
resistance:
Θ
CA
= Θ
CS
+Θ
SA
(Equation 2)
Where:
Θ
CS
= Thermal resistance of the thermal interface material (°C/W)
Θ
SA
= Thermal resistance from heatsink-to-local ambient (°C/W)
Θ
CS
is strongly dependent on the thermal conductivity and thickness of the TIM between the
heatsink and IHS.
Θ
SA
is a measure of the thermal resistance from the bottom of the heatsink to the local ambient air.
Θ
SA
is dependent on the heatsink’s material, thermal conductivity, and geometry. It is also strongly
dependent on the air velocity through the fins of the heatsink.
Figure 2 illustrates the combination of the different thermal resistances.
Figure 2. Processor Thermal Resistance Relationships
Heatsink
Socket
Processor Package
(IHS)
Thermal Interface
Material
T
C
T
sink
T
A
θ
θθ
θ
sa
θ
θθ
θ
cs
θ
θθ
θ
ca
=
θ
θθ
θ
cs
+
θ
θθ
θ
sa