MPC7450EC datasheet(46/52 Pages) MOTOROLA

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MPC7450 RISC Microprocessor Hardware Speciﬁcations

MOTOROLA

System Design Information

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 7 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 24). 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 MPC7450. Of course, the

selection of any thermal interface material depends on many factors—thermal performance requirements,

manufacturability, service temperature, dielectric properties, cost, etc.

Figure 26. 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 upon 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:

Dow-Corning Corporation

800-248-2481

Dow-Corning Electronic Materials

PO Box 0997

Midland, MI 48686-0997

Internet: www.dow.com

Chomerics, Inc.

781-935-4850

77 Dragon Court

Woburn, MA 01888-4014

Internet: www.chomerics.com

0.5

1.5

1020304050607080

Silicone Sheet (0.006 inch)

Bare Joint

Floroether Oil Sheet (0.007 inch)

Graphite/Oil Sheet (0.005 inch)

Synthetic Grease

Contact Pressure (psi)

Freescale Semiconductor, Inc.

For More Information On This Product,

Go to: www.freescale.com

IVE

D B

Y F

INC

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