MPC860DP FREESCALE [Freescale Semiconductor, Inc], MPC860DP Datasheet - Page 10

• Manufacturer Part Number: MPC860DP
• Description: Hardware Specifications
• Manufacturer: FREESCALE [Freescale Semiconductor, Inc]

Thermal Calculation and Measurement
printed circuit board surrounding the device. This thermal model is most useful for ceramic packages with heat sinks
where some 90% of the heat flows through the case and the heat sink to the ambient environment. For most
packages, a better model is required.
7.3 Estimation with Junction-to-Board Thermal Resistance
A simple package thermal model which has demonstrated reasonable accuracy (about 20%) is a two-resistor model
consisting of a junction-to-board and a junction-to-case thermal resistance. The junction-to-case thermal resistance
covers the situation where a heat sink is used or where a substantial amount of heat is dissipated from the top of the
package. The junction-to-board thermal resistance describes the thermal performance when most of the heat is
conducted to the printed circuit board. It has been observed that the thermal performance of most plastic packages,
especially PBGA packages, is strongly dependent on the board temperature; see
If the board temperature is known, an estimate of the junction temperature in the environment can be made using
the following equation:
where:
If the board temperature is known and the heat loss from the package case to the air can be ignored, acceptable
predictions of junction temperature can be made. For this method to work, the board and board mounting must be
similar to the test board used to determine the junction-to-board thermal resistance, namely a 2s2p (board with a
power and a ground plane) and by attaching the thermal balls to the ground plane.
10
R
T
P
D
B
θJB
= board temperature (ºC)
= power dissipation in package
= junction-to-board thermal resistance (ºC/W)
T
J
= T
B
Figure 1. Effect of Board Temperature Rise on Thermal Behavior
+ (R
θJB
× P
MPC860 Family Hardware Specifications, Rev. 7
Board Temperature Rise Above Ambient Divided by Package Power
D
)
Figure
1.
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