PPC8567ECVTAQJGA datasheet(128/139 Pages) FREESCALE

128 / 139 page

MPC8568E/MPC8567E PowerQUICC III Integrated Processor Hardware Specifications, Rev. 1

128

Freescale Semiconductor

Thermal

•

The die junction-to-board thermal resistance

Figure 71 depicts the primary heat transfer path for a package with an attached heat sink mounted to a

printed-circuit board.

Figure 71. Package with Heat Sink Mounted to a Printed-Circuit Board

The heat sink removes most of the heat from the device. 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. The junction-to-case thermal resistance is low enough that the heat sink attach

material and heat sink thermal resistance are the dominant terms.

24.2.3

Thermal Interface Materials

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

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

Figure 72 shows the thermal performance of three thin-sheet thermal-interface materials (silicone,

graphite/oil, floroether oil), a bare joint, and a joint with thermal grease as a function of contact pressure.

As shown, the performance of these thermal interface materials improves with increasing contact pressure.

The use of thermal grease significantly reduces the interface thermal resistance. The bare joint results in a

thermal resistance approximately six times greater than the thermal grease joint.

Heat sinks are attached to the package by means of a spring clip to holes in the printed-circuit board (see

Figure 69). Therefore, the synthetic grease offers the best thermal performance, especially at the low

interface pressure.

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)

PPC8567ECVTAQJGA Datasheet(PDF) 128 Page - Freescale Semiconductor, Inc