MPC8610 Integrated Host Processor Hardware Specifications, Rev. 2
Hardware Design Considerations
Freescale Semiconductor
86
Tyco Electronics
800-522-6752
Chip Coolers
P.O. Box 3668
Harrisburg, PA 17105-3668
Internet: www.chipcoolers.com
Wakefield Engineering
603-635-5102
33 Bridge St.
Pelham, NH 03076
Internet: www.wakefield.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.
3.12.2.1
Internal Package Conduction Resistance
For the exposed-die packaging technology described in
Table 62, the intrinsic conduction thermal resistance paths are as
follows:
The die junction-to-case thermal resistance
The die junction-to-board thermal resistance
Figure 55 depicts the primary heat transfer path for a package with an attached heat sink mounted to a printed-circuit board.
Figure 55. C4 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.
3.12.2.2
Thermal Interface Materials
A thermal interface material is recommended at the package-to-heat sink interface to minimize the thermal contact resistance.
Figure 56 shows the thermal performance of three thin-sheet thermal-interface materials (silicone, graphite/oil, fluoroether 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. In contrast, the bare joint results in a thermal resistance approximately seven times greater than the thermal
grease joint.
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.)