mpc5644a Freescale Semiconductor, Inc, mpc5644a Datasheet - Page 77

• Manufacturer Part Number: mpc5644a
• Description: Mpc5644a Microcontroller Data Sheet
• Manufacturer: Freescale Semiconductor, Inc

The thermal resistance is expressed as the sum of a junction-to-case thermal resistance plus a case-to-ambient thermal
resistance:
where:
R
case-to-ambient thermal resistance, R
mounting arrangement on the 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 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 (
the following equation:
where:
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. Place a small amount of epoxy on the thermocouple junction and approximately 1 mm of wire extending from
the junction. Place the thermocouple wire flat against the package case to avoid measurement errors caused by the cooling
effects of the thermocouple wire.
References:
Semiconductor Equipment and Materials International
3081 Zanker Road
San Jose, CA 95134
USA
[phone]
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.
Freescale Semiconductor
JC
•
•
is device related and is not affected by other factors. The thermal environment can be controlled to change the
R
R
R
T

P
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.
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.
D
T
JA
JC
CA
JT
= thermocouple temperature on top of the package (
= power dissipation in the package (W)
JT
= thermal characterization parameter (
= junction-to-case thermal resistance (
= junction-to-ambient thermal resistance (
= case to ambient thermal resistance (
) to determine the junction temperature by measuring the temperature at the top center of the package case using
CA
Preliminary—Subject to Change Without Notice
MPC5644A Microcontroller Data Sheet, Rev. 4
. For example, change the air flow around the device, add a heat sink, change the
T
R
J
JA
= T
o
o
o
C/W)
C/W)
C/W)
= R
T
o
+ (
C/W)
JC
JT
+ R
o
x P
C)
CA
D
)
Electrical characteristics
Eqn. 3
Eqn. 4
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