MPC8560CPXAPDB datasheet(93/108 Pages) FREESCALE

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MPC8560 Integrated Processor Hardware Specifications, Rev. 3.1

Freescale Semiconductor

Thermal

Figure 55. Thermalloy #2328B Heat Sink-to-Ambient Thermal Resistance Versus Airflow Velocity

16.2.4.2Case 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 56 and Figure 57.

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.

The spring mounting should be designed to apply the force only directly above the die. By localizing the force,

rocking of the heat sink is minimized. One suggested mounting method attaches a plastic fence to the board to

provide the structure on which the heat sink spring clips. The plastic fence also provides the opportunity to minimize

0.5

1.5

2.5

3.5

Thermalloy #2328B Pin-fin Heat Sink

Approach Air Velocity (m/s)

(25

× 28 × 15 mm)

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