MPC8560 datasheet(90/108 Pages) FREESCALE

90 / 108 page

MPC8560 Integrated Processor Hardware Specifications, Rev. 3.1

Freescale Semiconductor

Thermal

16.2.2 Internal Package Conduction Resistance

For the packaging technology, shown in Table 59, the intrinsic internal conduction thermal resistance paths are as

follows:

•

The die junction-to-case thermal resistance

•

The die junction-to-board thermal resistance

Figure 53 depicts the primary heat transfer path for a package with an attached heat sink mounted to a printed-circuit

board.

Figure 53. 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 and through the lid, 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.

16.2.3 Adhesives and 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 54 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 51).

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)

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