C5ENPB0-DS Datasheet, PDF (81/118 Pages) Freescale Semiconductor, Inc – C-5e Network Processor Silicon Revision B0

Power and Thermal Characteristics
81
Figure 11 Package with Heat Sink Mounted to the Printed Circuit Board
External Resistance
Radiation Convection
Heat Sink
Internal Resistance
Printed Circuit Board (PCB)
Thermal Interface Material
Die/Package
Die Junction
Package/Leads
FREESCALE SEMICONDUCTOR
External Resistance
Radiation Convection
Heat generated on the active side of the chip is conducted through the silicon, then
through the heat sink attach material (or thermal interface material), and finally to the
heat sink where it is removed by convection.
Because the silicon thermal resistance is quite small, for a first-order analysis, the
temperature drop in the silicon may be neglected. Thus, the thermal interface material
and the heat sink conduction/convective thermal resistances are the dominant terms.
Heat Sink Selection Example
For preliminary heat sink sizing, the die-junction temperature can be expressed as follows:
T _j = T _a + T _r + (θ_jc + θ_int + θ_sa) x P _d
where:
T _j is the die-junction temperature
T _a is the inlet cabinet ambient temperature
T _r is the air temperature rise within the computer cabinet
C5ENPB0-DS REV 08