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Ultim ately, th e fin al selection of an appropriate h eat sin k for th e PPC740 an d PPC750
depen ds on m an y factors, su ch as th erm al perform an ce at a given air velocity, spatial
volu m e, m ass, attach m en t m eth od, assem bly, an d cost.
8.7.1 Internal Package Conduction Resistance
For th e exposed-die packagin g tech n ology, sh own in Table 3 , th e in trin sic con du ction
th erm al resistan ce path s are as follows:
•Th e die ju n ction -to-case th erm al resistan ce
•Th e die ju n ction -to-lead th erm al resistan ce
Figu re 20 depicts th e prim ary h eat tran sfer path for a package with an attach ed h eat
sin k m ou n ted to a prin ted-circu it board.
External Resistance
Radiation
Convection
Heat Sink
Thermal Interface Material
Die/Package
Chip Junction
Internal Resistance
Package/Leads
Printed-Circuit Board
Radiation
Convection
External Resistance
(Note th e in tern al versu s extern al package resistan ce)
Figure 20. C4 Package with Heat Sink Mounted to a Printed-Circuit Board
Heat gen erated on th e active side (ball) of th e ch ip is con du cted th rou gh th e silicon ,
PPC740 and PPC750 Hardware Specifications
38 of 44
Preliminary and subject to change without notice
IBM [ IBM ]
