MPC7457EC datasheet(58/68 Pages) FREESCALE

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MPC7457 RISC Microprocessor Hardware Specifications, Rev. 5

Freescale Semiconductor

System Design Information

interface thermal resistance. That is, the bare joint results in a thermal resistance approximately seven times greater

than the thermal grease joint.

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

Figure 25). Therefore, the synthetic grease offers the best thermal performance, considering the low interface

pressure and is recommended due to the high power dissipation of the MPC7457. Of course, the selection of any

thermal interface material depends on many factors—thermal performance requirements, manufacturability, service

temperature, dielectric properties, cost, etc.

Figure 29. Thermal Performance of Select Thermal Interface Material

The board designer can choose between several types of thermal interface. Heat sink adhesive materials should be

selected based on high conductivity, yet adequate mechanical strength to meet equipment shock/vibration

requirements. There are several commercially available thermal interfaces and adhesive materials provided by the

following vendors:

The Bergquist Company

800-347-4572

18930 West 78

th St.

Chanhassen, MN 55317

Internet: www.bergquistcompany.com

Chomerics, Inc.

781-935-4850

77 Dragon Ct.

Woburn, MA 01888-4014

Internet: www.chomerics.com

0.5

1.5

1020

50607080

Silicone Sheet (0.006 in.)

Bare Joint

Floroether Oil Sheet (0.007 in.)

Graphite/Oil Sheet (0.005 in.)

Synthetic Grease

Contact Pressure (psi)

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