C5EC3EARCH-RMSLASHD datasheet(77/114 Pages) FREESCALE

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Power and Thermal Characteristics

Figure 11 Package with Heat Sink Mounted to the Printed Circuit Board

Heat generated on the active side of the chip is conducted through the silicon, then

through the heat sink attach material (or thermal interface material), and finally to the

heat sink where it is removed by convection.

Because the silicon thermal resistance is quite small, for a first-order analysis, the

temperature drop in the silicon may be neglected. Thus, the thermal interface material

and the heat sink conduction/convective thermal resistances are the dominant terms.

Heat Sink Selection Example

For preliminary heat sink sizing, the die-junction temperature can be expressed as follows:

j = T a + T r + (θjc + θint + θsa ) x P d

where:

j is the die-junction temperature

a is the inlet cabinet ambient temperature

r is the air temperature rise within the computer cabinet

External Resistance

Internal Resistance

External Resistance

Radiation

Heat Sink

Printed Circuit Board (PCB)

Radiation

Convection

Thermal Interface Material

Die/Package

Die Junction

Package/Leads

Convection

Freescale Semiconductor, Inc.

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C5EC3EARCH-RM/D Datenblatt(PDF) 77 Page - Freescale Semiconductor, Inc