MPC8540CPX667JC datasheet(86/104 Pages) FREESCALE

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MPC8540 Integrated Processor Hardware Specifications, Rev. 4

Freescale Semiconductor

Thermal

Figure 48. Thermalloy #2328B Heat Sink-to-Ambient Thermal Resistance Versus Airflow Velocity

16.2.4.2 Case 2

Every system application has different conditions that the thermal management solution must solve. As an

alternate example, assume that the air reaching the component is 85

C with an approach velocity of 1

m/sec. For a maximum junction temperature of 105

C at 7 W, the total thermal resistance of junction to

case thermal resistance plus thermal interface material plus heat sink thermal resistance must be less than

2.8

C/W. The value of the junction to case thermal resistance in Table 59 includes the thermal interface

resistance of a thin layer of thermal grease as documented in footnote 4 of the table. Assuming that the

heat sink is flat enough to allow a thin layer of grease or phase change material, then the heat sink must be

less than 2

C/W.

Millennium Electronics (MEI) has tooled a heat sink MTHERM-1051 for this requirement assuming a

compactPCI environment at 1 m/sec and a heat sink height of 12 mm. The MEI solution is illustrated in

Figure 49 and Figure 50. This design has several significant advantages:

•

The heat sink is clipped to a plastic frame attached to the application board with screws or plastic

inserts at the corners away from the primary signal routing areas.

•

The heat sink clip is designed to apply the force holding the heat sink in place directly above the

die at a maximum force of less than 10 lbs.

•

For applications with significant vibration requirements, silicone damping material can be applied

between the heat sink and plastic frame.

00.511.522.533.5

Thermalloy #2328B Pin-fin Heat Sink

Approach Air Velocity (m/s)

(25

× 28 × 15 mm)

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