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MPC8240 Integrated Processor Hardware Specifications
System Design Information
Shin-Etsu MicroSi, Inc.
888-642-7674
10028 S. 51st St.
Phoenix, AZ 85044
Internet: www.microsi.com
Thermagon Inc.
888-246-9050
4707 Detroit Ave.
Cleveland, OH 44102
Internet: www.thermagon.com
The following section provides a heat sink selection example using one of the commercially-available heat
sinks.
1.7.8.3
Heat Sink Selection Example
For preliminary heat sink sizing, the die-junction temperature, TJ, can be expressed as follows:
TJ = TA + TR + (RθJC + RθINT + RθSA) × PD
where
TJ is the die-junction temperature
TA is the inlet cabinet ambient temperature
TR is the air temperature rise within the computer cabinet
RθJC is the junction-to-case thermal resistance
RθINT is the adhesive or interface material thermal resistance
RθSA is the heat sink base-to-ambient thermal resistance
PD is the power dissipated by the device
During operation, the die-junction temperatures (TJ) should be maintained at less than the value specified
in
Table 2. The temperature of the air cooling the component greatly depends on the ambient inlet air
temperature and the air temperature rise within the electronic cabinet. An electronic cabinet inlet-air
temperature (TA) may range from 30° to 40°C. The air temperature rise within a cabinet (TR) may be in the
range of 5° to 10°C. The thermal resistance of the thermal interface material (RθINT) is typically about
1°C/W. Assuming a TA of 30°C, a TR of 5°C, a TBGA package RθJC = 1.8, and a power consumption (PD)
of 5.0 watts, the following expression for TJ is obtained for die-junction temperature:
TJ = 30°C + 5°C + (1.8°C/W + 1.0°C/W + RθSA) × 5.0 W
For preliminary heat sink sizing, the heat sink base-to-ambient thermal resistance is needed from the heat
sink manufacturer.
Though the die junction-to-ambient and the heat sink-to-ambient thermal resistances are a common figure
of merit used for comparing the thermal performance of various microelectronic packaging technologies,
one should exercise caution when using only this metric in determining thermal management because no
single parameter can adequately describe three-dimensional heat flow. The final die-junction operating
temperature is not only a function of the component-level thermal resistance, but the system-level design
and its operating conditions. In addition to the component's power consumption, a number of factors affect
the final operating die-junction temperature: airflow, board population (local heat flux of adjacent
components), heat sink efficiency, heat sink attach, heat sink placement, next-level interconnect technology,
system air temperature rise, altitude, and so on.
Due to the complexity and the many variations of system-level boundary conditions for today’s
microelectronic equipment, the combined effects of the heat transfer mechanisms (radiation, convection,
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Freescale Semiconductor, Inc.
For More Information On This Product,
Go to: www.freescale.com
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