MPC5553_07 datasheet(8/66 Pages) FREESCALE

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MPC5553 Microcontroller Data Sheet, Rev. 2.0

Electrical Characteristics

Freescale Semiconductor

RθJC is device related and is not affected by other factors. The thermal environment can be controlled to

change the case-to-ambient thermal resistance, RθCA. For example, change the air flow around the device,

add a heat sink, change the mounting arrangement on printed circuit board, or change the thermal

dissipation on the printed circuit board surrounding the device. This description is most useful for

packages with heat sinks where 90% of the heat flow is through the case to the heat sink to ambient. For

most packages, a better model is required.

A more accurate two-resistor thermal model can be constructed from the junction-to-board thermal

resistance and the junction-to-case thermal resistance. The junction-to-case thermal resistance describes

when using a heat sink 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. This model can be used to generate simple estimations and for

computational fluid dynamics (CFD) thermal models.

To determine the junction temperature of the device in the application on a prototype board, use the

thermal characterization parameter (

ΨJT) to determine the junction temperature by measuring the

temperature at the top center of the package case using the following equation:

TJ = TT + (ΨJT × PD)

where:

TT = thermocouple temperature on top of the package (oC)

ΨJT = thermal characterization parameter (oC/W)

PD = power dissipation in the package (W)

The thermal characterization parameter is measured in compliance with the JESD51-2 specification using

a 40-gauge type T thermocouple epoxied to the top center of the package case. Position the thermocouple

so that the thermocouple junction rests on the package. A small amount of epoxy is placed on the

thermocouple junction and approximately 1 mm of wire extending from the junction. The thermocouple

wire is placed flat against the package case to avoid measurement errors caused by the cooling effects of

the thermocouple wire.

References:

Semiconductor Equipment and Materials International

805 East Middlefield Rd.

Mountain View, CA., 94043

(415) 964-5111

MIL-SPEC and EIA/JESD (JEDEC) specifications are available from Global Engineering Documents at

800-854-7179 or 303-397-7956.

JEDEC specifications are available on the web at 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. G. Kromann, S. Shidore, and S. Addison, “Thermal Modeling of a PBGA for Air-Cooled

Applications,” Electronic Packaging and Production, pp. 53–58, March 1998.

•

3. 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.

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