Intel
®
Pentium
®
III Processor in the FC-PGA2 Package Thermal Design Guidelines
R
249660-001
23
7.
Thermal Metrology for FC-PGA2
Packaged Processors
The following sections will discuss the thermal metrology used on the FC-PGA2 packaged processors.
These techniques should be followed to evaluate thermal performance of proposed solutions. Carefully
read the following instructions and interpretation steps to validate your cooling solution.
7.1. Thermal
Resistance
The thermal resistance value from case to local-ambient (
θ
CA
) for a FC-PGA2 package 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 case-to-sink thermal
resistance (
θ
CS
), and the sink to local-ambient thermal resistance (
θ
SA
) (see Figure 7-1). The
θ
CS
value is
strongly dependent on the thermal conductivity and thickness of the TIM between the heatsink and
surface of the processor.
θ
SA
is a measure of the thermal resistance from the bottom of the heatsink cooling solution to the local-
ambient air.
θ
SA
is dependent on the heatsink’s material, thermal conductivity, and geometry, and is
strongly dependent on the air velocity through the fins of the heatsink.
Figure 7-1. Processor-Heatsink Thermal Resistance Relationships
Heatsink
Socket
Processor Package
(IHS)
Thermal Interface
Material
T
case
T
sink
T
ambient
θθθθ
sa
θθθθ
cs
θθθθ
ca
=
θθθθ
cs
+
θθθθ
sa
The thermal parameters are related by the following equations:
Equation 1. Case to Ambient Thermal Resistance
θ
CA
= (T
CASE
- T
LA
) / TDP
