PowerPC 750 SCM RISC Microprocessor
PID8p-750
Preliminary Copy
Dow-Corning Corporation
Dow-Corning Electronic Materials
P.O. Box 0997
517-496-4000
Midland, MI 48686-0997
Chomerics, Inc.
77 Dragon Court
Woburn, MA 01888-4850
617-935-4850
216-741-7659
860-571-5100
609-882-2332
Thermagon, Inc.
3256 West 25th Street
Cleveland, OH 44109-1668
Loctite Corporation
1001 Trout Brook Crossing
Rocky Hill, CT 06067
AI Technology (e.g. EG7655)
1425 Lower Ferry Road
Trent, NJ 08618
The following section provides a heat sink selection example using one of the commercially available heat
sinks.
Heat Sink Selection Example
For preliminary heat sink sizing, the die-junction temperature can be expressed as follows.
TJ = TA + TR + (θJC + θINT + θSA) × PD
Where:
TJ is the die-junction temperature
TA is the inlet cabinet ambient temperature
TR is the air temperature rise within the system cabinet
θJC is the junction-to-case thermal resistance
θINT is the thermal resistance of the thermal interface material
θSA is the heat sink-to-ambient thermal resistance
PD is the power dissipated by the device
Typical die-junction temperatures (TJ) should be maintained less than the value specified in Table “Package
Thermal Characteristics,” on page 7. The temperature of the air cooling the component greatly depends upon
the ambient inlet air temperature and the air temperature rise within the computer cabinet. An electronic cab-
inet inlet-air temperature (TA) may range from 30 to 40°C. The air temperature rise within a cabinet (TR) may
be in the range of 5 to 10°C. The thermal resistance of the interface material (θINT) is typically about 1°C/W.
Assuming a TA of 30°C, a TR of 5°C, a CBGA package θJC = 0.03, and a power dissipation (PD) of 5.0 watts, the
following expression for TJ is obtained.
Die-junction temperature: TJ = 30°C + 5°C + (0.03°C/W +1.0°C/W + θSA) × 5W
For a Thermalloy heat sink #2328B, the heat sink-to-ambient thermal resistance (θSA) versus air flow velocity
is shown in Figure 21.
Page 38
Version 2.0
Datasheet
9/30/99
IBM [ IBM ]
