DD 2.X
Preliminary
PowerPC 750FX RISC Microprocessor
Figure 5-8. Thermalloy #2328B Pin-Fin Heat Sink-to-Ambient Thermal Resistance vs. 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)
Assuming an air velocity of 0.5m/s, we have an effective θSA of 7°C/W, thus
TJ = 30°C + 5°C + (2.2°C/W +1.0°C/W + 7°C/W) × 4.5W,
resulting 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 may or may not need 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 technolo-
gies, one should exercise caution when only using 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 might include air flow, board population (local heat flux of
adjacent components), heat sink efficiency, heat sink attach, next-level interconnect technology, system air
temperature rise, and so forth.
Body_750FX_DS_DD2.X.fm.2.0
June 9, 2003
5. System Design Information
Page 51 of 63
IBM [ IBM ]
