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7
Fins and Heat Sinks
Consider the surface area A shown in Figure 7.1a. This can be the top surface of an
electronic package, the surface of a heat spreader that is attached to multiple elec-
tronic components of a board, or the external surface of an electronic system such as
a handheld computer or a pole-mount wireless radio unit. The total heat transfer rate
from this surface is equal to the sum of convection and radiation heat transfer rates
given by Equations 4.4 and 4.18 in Chapter 4:
QQ QhAT ThAT T
ss
=+=−+
′
−
conv radconv ∞rad ∞
()(),,
(7.1)
or
(7.2)
where
(7.3)
is called the combined heat tra ...