Thermal
where:
R
R
R
= junction-to-ambient thermal resistance (°C/W)
= junction-to-case thermal resistance (°C/W)
= case-to-ambient thermal resistance (°C/W)
θJA
θJC
θCA
RθJC is device-related and cannot be influenced by the user. The user controls the thermal environment to
change the case-to-ambient thermal resistance, RθCA. For instance, the user can change the size of the heat
sink, the air flow around the device, the interface material, the mounting arrangement on printed-circuit
board, or change the thermal dissipation on the printed-circuit board surrounding the device.
The thermal performance of devices with heat sinks has been simulated with a few commercially available
heat sinks. The heat sink choice is determined by the application environment (temperature, air flow,
adjacent component power dissipation) and the physical space available. Because there is not a standard
application environment, a standard heat sink is not required.
Table 64 shows heat sink thermal resistance for TBGA of the MPC8349EA.
Table 64. Heat Sink and Thermal Resistance of MPC8349EA (TBGA)
35 × 35 mm TBGA
Heat Sink Assuming Thermal Grease
Air Flow
Thermal Resistance
AAVID 30 × 30 × 9.4 mm pin fin
Natural convection
1 m/s
10
6.5
5.6
8.4
4.7
4
AAVID 30 × 30 × 9.4 mm pin fin
AAVID 30 × 30 × 9.4 mm pin fin
2 m/s
AAVID 31 × 35 × 23 mm pin fin
Natural convection
1 m/s
AAVID 31 × 35 × 23 mm pin fin
AAVID 31 × 35 × 23 mm pin fin
2 m/s
Wakefield, 53 × 53 × 25 mm pin fin
Natural convection
1 m/s
5.7
3.5
2.7
6.7
4.1
2.8
3.1
Wakefield, 53 × 53 × 25 mm pin fin
Wakefield, 53 × 53 × 25 mm pin fin
2 m/s
MEI, 75 × 85 × 12 no adjacent board, extrusion
MEI, 75 × 85 × 12 no adjacent board, extrusion
MEI, 75 × 85 × 12 no adjacent board, extrusion
MEI, 75 × 85 × 12 mm, adjacent board, 40 mm side bypass
Natural convection
1 m/s
2 m/s
1 m/s
Accurate thermal design requires thermal modeling of the application environment using computational
fluid dynamics software which can model both the conduction cooling and the convection cooling of the
air moving through the application. Simplified thermal models of the packages can be assembled using the
junction-to-case and junction-to-board thermal resistances listed in the thermal resistance table. More
detailed thermal models can be made available on request.
MPC8349EA PowerQUICC II Pro Integrated Host Processor Hardware Specifications, Rev. 13
Freescale Semiconductor
77
FREESCALE [ Freescale ]
