Thermal
8
7
Heat Sink Thermal Resistance (°C/W)
Thermalloy #2328B Pin-fin Heat Sink
(25
×
28
×
15 mm)
6
5
4
3
2
1
0
0.5
1
1.5
2
2.5
3
3.5
Approach Air Velocity (m/s)
Figure 48. Thermalloy #2328B Heat Sink-to-Ambient Thermal Resistance Versus Airflow Velocity
16.2.4.2 Case 2
Every system application has different conditions that the thermal management solution must solve. As an
alternate example, assume that the air reaching the component is 85 C with an approach velocity of 1
m/sec. For a maximum junction temperature of 105 C at 7 W, the total thermal resistance of junction to
case thermal resistance plus thermal interface material plus heat sink thermal resistance must be less than
2.8 C/W. The value of the junction to case thermal resistance in
includes the thermal interface
resistance of a thin layer of thermal grease as documented in footnote 4 of the table. Assuming that the
heat sink is flat enough to allow a thin layer of grease or phase change material, then the heat sink must be
less than 2 C/W.
Millennium Electronics (MEI) has tooled a heat sink MTHERM-1051 for this requirement assuming a
compactPCI environment at 1 m/sec and a heat sink height of 12 mm. The MEI solution is illustrated in
and
This design has several significant advantages:
• The heat sink is clipped to a plastic frame attached to the application board with screws or plastic
inserts at the corners away from the primary signal routing areas.
• The heat sink clip is designed to apply the force holding the heat sink in place directly above the
die at a maximum force of less than 10 lbs.
• For applications with significant vibration requirements, silicone damping material can be applied
between the heat sink and plastic frame.
MPC8540 Integrated Processor Hardware Specifications, Rev. 4
86
Freescale Semiconductor
FREESCALE [ FREESCALE SEMICONDUCTOR, INC ]
