MPC7410 datasheet(44/56 Pages) FREESCALE

44 / 56 page

MPC7410 RISC Microprocessor Hardware Specifications, Rev. 6.1

Freescale Semiconductor

System Design Information

8.8.1 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 28 depicts the primary heat transfer path for a package with an attached 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.

Since the silicon thermal resistance is quite small, for a first-order analysis, the temperature drop in the silicon may

be neglected. Thus, the heat sink attach material and the heat sink conduction/convective thermal resistances are the

dominant terms.

Figure 28. C4 Package with Heat Sink Mounted to a Printed-Circuit Board

8.8.2 Adhesives and 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 29 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. That is, the bare joint results in a thermal resistance approximately seven 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 26).

This spring force should not exceed 5.5 pounds of force. Therefore, the synthetic grease offers the best thermal

performance, considering the low interface pressure. Of course, the selection of any thermal interface material

depends on many factors—thermal performance requirements, manufacturability, service temperature, dielectric

properties, cost, and so on.

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

MPC7410 Arkusz danych(PDF) 44 Page - Freescale Semiconductor, Inc

MPC7410 Arkusz danych(HTML) 44 Page - Freescale Semiconductor, Inc

Html Pages

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56

Arkusz danych Pobierz

Link URL