MPC8360CVVALFHA datasheet(93/102 Pages) FREESCALE

93 / 102 page

MPC8360E/MPC8358E PowerQUICC II Pro Processor Revision 2.x TBGA Silicon Hardware Specifications, Rev. 5

Freescale Semiconductor

Thermal Management Information

TJ = TB + (RθJB × PD)

where:

TJ = junction temperature (° C)

TB = board temperature at the package perimeter (° C)

RθJA = junction to board thermal resistance (° C/W) per JESD51-8

PD = power dissipation in the package (W)

When the heat loss from the package case to the air can be ignored, acceptable predictions of junction temperature can be made.

The application board should be similar to the thermal test condition: the component is soldered to a board with internal planes.

22.2.3

Experimental Determination of Junction Temperature

To determine the junction temperature of the device in the application after prototypes are available, the Thermal

Characterization Parameter (

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:

TJ = TT + (ΨJT × PD)

where:

TJ = junction temperature (° C)

TT = thermocouple temperature on top of package (° C)

JT = junction-to-ambient thermal resistance (° C/W)

PD = power dissipation in the package (W)

The thermal characterization parameter is measured per JESD51-2 specification 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 caused by cooling effects

of the thermocouple wire.

22.2.4

Heat Sinks and Junction-to-Ambient Thermal Resistance

In some application environments, a heat sink is required to provide the necessary thermal management of the device. When a

heat sink is used, the thermal resistance is expressed as the sum of a junction to case thermal resistance and a case to ambient

thermal resistance:

RθJA = RθJC + RθCA

where:

RθJA = junction-to-ambient thermal resistance (° C/W)

RθJC = junction-to-case thermal resistance (° C/W)

RθCA = case-to-ambient thermal resistance (° C/W)

RθJC is device related and cannot be influenced by the user. The user controls the thermal environment to change the

case-to-ambient thermal resistance, RθCA. For instance, the user can change the size of the heat sink, the airflow around the

device, the interface material, the mounting arrangement on printed-circuit board, or change the thermal dissipation on the

printed-circuit board surrounding the device.

To illustrate the thermal performance of the devices with heat sinks, the thermal performance has been simulated with a few

commercially available heat sinks. The heat sink choice is determined by the application environment (temperature, airflow,

adjacent component power dissipation) and the physical space available. Because there is not a standard application

environment, a standard heat sink is not required.

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