PowerPC 750FL RISC Microprocessor
Preliminary
Figure 5-8. Thermalloy #2328B Pin-Fin Heat Sink-to-Ambient Thermal Resistance Versus Airflow Velocity
Thermalloy #2328B Pin-fin Heat Sink
(25 x 28 x 15 mm)
8
7
6
5
4
3
2
1
0
0.5
1
1.5
2
2.5
3
3.5
Approach Air Velocity (m/s)
For air velocity of 0.5 m/s, and an effective θSA of 7°C/W, the junction temperature is given by
TJ = 30°C + 5°C + (2.2°C/W + 1.0°C/W + 7°C/W) × 4.5 W
This results in a junction temperature of approximately 81°C which is well within the maximum operating
temperature of the component.
Other heat sinks offered by Chip Coolers, IERC, Thermalloy, Aavid, and Wakefield Engineering offer different
heat sink-to-ambient thermal resistances, and might or might not require air flow.
Though the junction-to-ambient and the heat sink-to-ambient thermal resistances are a common figure of
merit used for comparing the thermal performance of various microelectronic packaging technologies, exer-
cise caution when using only this metric in determining thermal management because no single parameter
can adequately describe three-dimensional heat flow. The final chip junction operating temperature is not
only a function of the component-level thermal resistance, but the system-level design and its operating
conditions. In addition to the component's power dissipation, a number of factors affect the final operating die
junction temperature. These factors can include air flow, board population (local heat flux of adjacent compo-
nents), heat sink efficiency, heat sink attachment method, next-level interconnect technology, system air
temperature rise, and so forth.
System Design Information
Page 58 of 65
750flds60.fm.6.0
April 27, 2007
IBM [ IBM ]
