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.
T = T + (R
× P )
D
J
C
θJC
where:
T = junction temperature (°C)
J
T = case temperature of the package (°C)
C
™
MPC8378E PowerQUICC II Pro Processor Hardware Specifications, Rev. 2
118
Freescale Semiconductor
FREESCALE [ Freescale ]
