
Fins and Heat Sinks 157
The heat sink efficiency is
ηη
t
ff
t
f
NA
A
=− −=−
×
−111
64 0 00029
0 0217
1
2
2
()
.
.
(
m
m
00 974 0 978.).,=
and the heat sink convection-radiation thermal resistance is
R
hA
hs cr
tt
,
..
.==
××
=
11
0 978 25 0 0217
188
2
η W/m°Cm
2
°°C/W.
The conduction thermal resistance through the heat sink base is
R
t
kWH
hs b
b
,
.
..
.==
××
=
0 004
390 006006
000
m
W/m°Cmm
228°C/W.
The spreading thermal resistance is calculated using the correlation given in
Section 5.7 and the effective heat transfer coefficient:
h
RA
hs cr hsb
eff
o
C/Wmm
==
××
=
11
188006 006
147
,
...
.88W/m °C.
2
r
A
r
A
c
s
1
2
2
2
0 0113== =
==
×
ππ
ππ
0.0004m
m
0.06 0.06 m
.
== 0 0338.m
ε
τ
== =
==
r
r
t
r
b
1
2
2
0 0113
0 0338
0 334
0 004
00
.