Electrical Characteristics
MPC561/MPC563 Reference Manual, Rev. 1.2
Freescale Semiconductor
F-5
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.
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. Consultation on the creation of the
complex model is available.
To determine the junction temperature of the device in the application after prototypes are available, the
thermal characterization parameter (
ΨJT) 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:
TJ = TT + (ΨJT x PD)
where:
TT = thermocouple temperature on top of package (°C)
ΨJT = thermal characterization parameter
PD = 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 one mm of wire extending from the junction. The
thermocouple wire is placed flat against the package case to avoid measurement errors caused by cooling
effects of the thermocouple wire.
F.3.1
Thermal References
The website for Semiconductor Equipment and Materials International is www.semi.org and their global
headquarters address is: 3081 Zanker Road, San Jose CA, 95134; 1-408-943-6900.
MIL-SPEC and EIA/JESD (JEDEC) specifications are available from Global Engineering Documents on
the WEB at www.global.ihs.com or 800-854-7179 or 303-397-7956.
JEDEC specifications are available on the WEB at 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.