MPC8378E datasheet(118/126 Pages) FREESCALE

118 / 126 page

MPC8378E PowerQUICC™ II Pro Processor Hardware Specifications, Rev. 2

118

Freescale Semiconductor

Thermal

Tyco Electronics

Chip Coolers™

www.chipcoolers.com

Wakefield Engineering

www.wakefield.com

Interface material vendors include the following:

Chomerics, Inc.

www.chomerics.com

Dow-Corning Corporation

Dow-Corning Electronic Materials

www.dowcorning.com

Shin-Etsu MicroSi, Inc.

www.microsi.com

The Bergquist Company

www.bergquistcompany.com

23.3

Heat Sink Attachment

The device requires the use of heat sinks. When heat sinks are attached, an interface material is required,

preferably thermal grease and a spring clip. The spring clip should connect to the printed circuit board,

either to the board itself, to hooks soldered to the board, or to a plastic stiffener. Avoid attachment forces

that can lift the edge of the package or peel the package from the board. Such peeling forces reduce the

solder joint lifetime of the package. The recommended maximum compressive force on the top of the

package is 10 lb force (4.5 kg force). Any adhesive attachment should attach to painted or plastic surfaces,

and its performance should be verified under the application requirements.

23.3.1

Experimental Determination of the Junction Temperature with a

Heat Sink

When a heat sink is used, the junction temperature is determined from a thermocouple inserted at the

interface between the case of the package and the interface material. A clearance slot or hole is normally

required in the heat sink. Minimize the size of the clearance to minimize the change in thermal

performance caused by removing part of the thermal interface to the heat sink. Because of the experimental

difficulties with this technique, many engineers measure the heat sink temperature and then back calculate

the case temperature using a separate measurement of the thermal resistance of the interface. From this

case temperature, the junction temperature is determined from the junction to case thermal resistance.

TJ = TC + (RθJC × PD)

where:

TJ = junction temperature (°C)

TC = case temperature of the package (°C)

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