Datasheet

MPC852T PowerQUICC™ Hardware Specifications, Rev. 4
Freescale Semiconductor 11
References
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 vias attaching the thermal balls to the ground
plane.
7.4 Estimation Using Simulation
When the board temperature is not known, a thermal simulation of the application is needed. The simple
two-resistor model can be used with the thermal simulation of the application [2], or a more accurate and
complex model of the package can be used in the thermal simulation.
7.5 Experimental Determination
To determine the junction temperature of the device in the application after prototypes are available, the
thermal characterization parameter (Ψ
JT
) can be used to determine the junction temperature with a
measurement of the temperature at the top center of the package case using the following equation:
T
J
= T
T
+ (Ψ
JT
× P
D
)
where:
Ψ
JT
= thermal characterization parameter
T
T
= thermocouple temperature on top of package
P
D
= power dissipation in package
The thermal characterization parameter is measured per JESD51-2 specification published by JEDEC
using a 40-gauge type T thermocouple epoxied to the top center of the package case. The thermocouple
should be positioned so that the thermocouple junction rests on the package. A small amount of epoxy is
placed over the thermocouple junction and over about 1 mm of wire extending from the junction. The
thermocouple wire is placed flat against the package case to avoid measurement errors that cooling effects
of the thermocouple wire cause.
8 References
Semiconductor Equipment and Materials International [phone]
805 East Middlefield Rd
Mountain View, CA 94043
MIL-SPEC and EIA/JESD (JEDEC) specifications 800-854-7179 or
(Available from Global Engineering documents) 303-397-7956
JEDEC Specifications http://www.jedec.org
1. C.E. Triplett and B. Joiner, “An Experimental Characterization of a 272 PBGA Within an
Automotive Engine Controller Module,” Proceedings of SemiTherm, San Diego, 1998, pp. 47–54.
2. B. Joiner and V. Adams, “Measurement and Simulation of Junction to Board Thermal Resistance
and Its Application in Thermal Modeling,” Proceedings of SemiTherm, San Diego, 1999,
pp. 212–220.