mpc755ed Freescale Semiconductor, Inc, mpc755ed Datasheet - Page 46

• Manufacturer Part Number: mpc755ed
• Description: Risc Microprocessor Hardware Specifications
• Manufacturer: Freescale Semiconductor, Inc

System Design Information
8.8.2
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,
(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
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, etc.
Figure 27
46
25). This spring force should not exceed 5.5 pounds of force. Therefore, the synthetic grease offers
describes the thermal performance of select thermal interface materials.
Adhesives and Thermal Interface Materials
Figure 27
(Note the internal versus external package resistance.)
Figure 26. C4 Package with Heat Sink Mounted to a Printed-Circuit Board
External Resistance
External Resistance
Internal Resistance
shows the thermal performance of three thin-sheet thermal-interface materials
MPC755 RISC Microprocessor Hardware Specifications, Rev. 8
Printed-Circuit Board
Heat Sink
Radiation
Radiation
Convection
Convection
Thermal Interface Material
Die/Package
Die Junction
Package/Leads
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