Th erm agon , In c.
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Loctite Corporation
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AI Tech n ology (e.g. EG7655)
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Th e followin g section provides a h eat sin k selection exam ple u sin g on e of th e com m er-
cially available h eat sin ks.
8.8 Heat Sink Selection Example
For prelim in ary h eat sin k sizin g, th e die-ju n ction tem peratu re can be expressed as fol-
lows:
Tj = Ta + T + ( θ + θ + θ ) * P
d
r
jc
int
sa
Wh ere:
Tj is th e die-ju n ction tem peratu re
Ta is th e in let cabin et am bien t tem peratu re
Tr is th e air tem peratu re rise with in th e system cabin et
θ is th e ju n ction -to-case th erm al resistan ce
jc
θ
θ
is th e th erm al resistan ce of th e th erm al in terface m aterial
is th e h eat sin k-to-am bien t th erm al resistan ce
int
sa
P is th e power dissipated by th e device
d
Typical die-ju n ction tem peratu res (Tj) sh ou ld be m ain tain ed less th an th e valu e speci-
fied in Table 3 . Th e tem peratu re of th e air coolin g th e com pon en t greatly depen ds
u pon th e am bien t in let air tem peratu re an d th e air tem peratu re rise with in th e com -
pu ter cabin et. An electron ic cabin et in let-air tem peratu re (Ta) m ay ran ge from 30 to 40
°C. Th e air tem peratu re rise with in a cabin et (Tr) m ay be in th e ran ge of 5 to 10 °C. Th e
th erm al resistan ce of th e in terface m aterial (θ ) is typically abou t 1 °C/ W. Assu m in g a
int
Ta of 30 °C, a Tr of 5 °C, a CBGA package θ = 0.03, an d a power dissipation (P ) of 5.0
jc
d
watts, th e followin g expression for Tj is obtain ed:
Die-junction temperature: Tj = 30 °C + 5 °C + (0.03 °C/W +1.0 °C/W + θ ) * 5 W
sa
For a Th erm alloy h eat sin k #2328B, th e h eat sin k-to-am bien t th erm al resistan ce (θ )
sa
versu s air flow velocity is sh own in Figu re 22 .
41 of 44
PPC740 and PPC750 Hardware Specifications
Preliminary and subject to change without notice
IBM [ IBM ]
