MPC7450EC datasheet(45/52 Pages) MOTOROLA

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MOTOROLA

MPC7450 RISC Microprocessor Hardware Speciﬁcations

System Design Information

Cool Innovations Inc.

905-760-1992

260 Spinnaker Way, Unit 8

Concord, Ontario L4K 4P9

Canada

Internet: www.coolinnovations.com

Ultimately, the ﬁnal selection of an appropriate heat sink depends on many factors, such as thermal

performance at a given air velocity, spatial volume, mass, attachment method, assembly, and cost.

1.9.9.1

Internal Package Conduction Resistance

For the exposed-die packaging technology, shown in Table 3, the intrinsic conduction thermal resistance

paths are as follows:

•

The die junction-to-case (or top-of-die for exposed silicon) thermal resistance

•

The die junction-to-ball thermal resistance

Figure 25 depicts the primary heat transfer path for a package with an attached heat sink mounted to a

printed-circuit board.

Figure 25. C4 Package with Heat Sink Mounted to a 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 forced-air

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.

1.9.9.2

Thermal Interface Materials

A thermal interface material is recommended at the package lid-to-heat sink interface to minimize the

thermal contact resistance. For those applications where the heat sink is attached by spring clip mechanism,

Figure 26 shows the thermal performance of three thin-sheet thermal-interface materials (silicone,

External Resistance

Internal Resistance

(Note the internal versus external package resistance)

Radiation

Convection

Radiation

Convection

Heat Sink

Printed-Circuit Board

Thermal Interface Material

Package/Leads

Die Junction

Die/Package

Freescale Semiconductor, Inc.

For More Information On This Product,

Go to: www.freescale.com

IVE

D B

Y F

INC

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