Datasheet

MPC8245 Integrated Processor Hardware Specifications, Rev. 10
52 Freescale Semiconductor
System Design
Wakefield Engineering 603-635-5102
33 Bridge St.
Pelham, NH 03076
Internet: www.wakefield.com
Selection of an appropriate heat sink depends on thermal performance at a given air velocity, spatial
volume, mass, attachment method, assembly, and cost. Other heat sinks offered by Aavid Thermalloy,
Alpha Novatech, IERC, Chip Coolers, and Wakefield Engineering offer different heat sink-to-ambient
thermal resistances and may or may not need airflow.
7.8.1 Internal Package Conduction Resistance
The intrinsic conduction thermal resistance paths for the TBGA cavity-down packaging technology shown
in Figure 29 are as follows:
• Die junction-to-case thermal resistance
• Die junction-to-ball thermal resistance
Figure 29 depicts the primary heat transfer path for a package with an attached heat sink mounted on a
printed-circuit board.
Figure 29. TBGA Package with Heat Sink Mounted to a Printed-Circuit Board
In a TBGA package, the active side of the die faces the printed-circuit board. Most of the heat travels
through the die, across the die attach layer, and into the copper spreader. Some of the heat is removed from
the top surface of the spreader through convection and radiation. Another percentage of the heat enters the
printed-circuit board through the solder balls. The heat is then removed from the exposed surfaces of the
board through convection and radiation. If a heat sink is used, a larger percentage of heat leaves through
the top side of the spreader.
External Resistance
External Resistance
Internal Resistance
Radiation Convection
Radiation Convection
Heat Sink
Printed-Circuit Board
Thermal Interface Material
Package/Leads
Die Junction
Die/Package
(Note the internal versus external package resistance)