Page 77 - Power Electronics Handbook

70 Thermal design

A Semiconductor

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contact
due to
bow in
tab
(a)

F4garc 2.7 Temperature contours at the heatsink-power device interface: (a) without thermal
grease; (b) with thermal grease

Table 2.1 compares the thermal resistance of some commonly used
components; diamond is used to cool some specialised devices operating at
high frequency.
Figure 2.8 illustrates curves which may be used to determine the thermal
resistance of a heatsink in any application. The left-hand set of curves gives
the power dissipation through the power semiconductor, and is similar to

'lhble 2.1 Comparison of thermal resistance of some typical materials

Thermal resistance
Material ("c CmMr)

Diamond 0.02 to 0.1
Copper 0.3
Aluminium 0.5
Solder 2.0
Thermal grease 130
Mica 150
Mylar 400
Still air 3000