MPC8309EC datasheet(75/82 Pages) FREESCALE

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MPC8309 PowerQUICC II Pro Integrated Communications Processor Family Hardware Specifications, Rev. 0

Freescale Semiconductor

Thermal

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



JT = thermal characterization parameter (C/W)

PD = power dissipation in 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.

24.1.5

Heat Sinks and Junction-to-Case 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 as shown in the following equation:

RJA =RJC +RCA

Eqn. 4

where:

RJA = junction-to-ambient thermal resistance (C/W)

RJC = junction-to-case thermal resistance (C/W)

RCA = case-to-ambient thermal resistance (C/W)

RJC is device related and cannot be influenced by the user. The user controls the thermal environment to

change the case-to-ambient thermal resistance, RCA. For instance, the user can change the size of the heat

sink, the air flow 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, air flow, adjacent component power dissipation) and the physical

space available. Because there is not a standard application environment, a standard heat sink is not

required.

Accurate thermal design requires thermal modeling of the application environment using computational

fluid dynamics software which can model both the conduction cooling and the convection cooling of the

air moving through the application. Simplified thermal models of the packages can be assembled using the

junction-to-case and junction-to-board thermal resistances listed in the thermal resistance table. More

detailed thermal models can be made available on request.

24.2

Heat Sink Attachment

When attaching heat sinks to these devices, an interface material is required. The best method is to use

thermal grease and a spring clip. The spring clip should connect to the printed-circuit board, either to the

board itself, to hooks soldered to the board, or to a plastic stiffener. Avoid attachment forces which would

lift the edge of the package or peel the package from the board. Such peeling forces reduce the solder joint

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