MPC8245EC datasheet(52/68 Pages) FREESCALE

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MPC8245 Integrated Processor Hardware Specifications, Rev. 10

Freescale Semiconductor

System Design

Wakefield Engineering

603-635-5102

33 Bridge St.

Pelham, NH 03076

Internet: www.wakefield.com

Selection of an appropriate heat sink depends on thermal performance at a given air velocity, spatial

volume, mass, attachment method, assembly, and cost. Other heat sinks offered by Aavid Thermalloy,

Alpha Novatech, IERC, Chip Coolers, and Wakefield Engineering offer different heat sink-to-ambient

thermal resistances and may or may not need airflow.

7.8.1

Internal Package Conduction Resistance

The intrinsic conduction thermal resistance paths for the TBGA cavity-down packaging technology shown

in Figure 29 are as follows:

•

Die junction-to-case thermal resistance

•

Die junction-to-ball thermal resistance

Figure 29 depicts the primary heat transfer path for a package with an attached heat sink mounted on a

printed-circuit board.

Figure 29. TBGA Package with Heat Sink Mounted to a Printed-Circuit Board

In a TBGA package, the active side of the die faces the printed-circuit board. Most of the heat travels

through the die, across the die attach layer, and into the copper spreader. Some of the heat is removed from

the top surface of the spreader through convection and radiation. Another percentage of the heat enters the

printed-circuit board through the solder balls. The heat is then removed from the exposed surfaces of the

board through convection and radiation. If a heat sink is used, a larger percentage of heat leaves through

the top side of the spreader.

External Resistance

Internal Resistance

Radiation

Convection

Radiation

Convection

Heat Sink

Printed-Circuit Board

Thermal Interface Material

Package/Leads

Die Junction

Die/Package

(Note the internal versus external package resistance)

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