Thermal
Figure 50. Exploded Views (2) of a Heat Sink Attachment using a Plastic Fence
The die junction-to-ambient and the heat sink-to-ambient thermal resistances are common figure-of-merits
used for comparing the thermal performance of various microelectronic packaging technologies, one
should exercise caution when only using 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), system air temperature rise, altitude, etc.
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
and conduction) may vary widely. For these reasons, we recommend using conjugate heat transfer models
for the boards, as well as, system-level designs.
MPC8540 Integrated Processor Hardware Specifications, Rev. 4
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