电子设备热设计(第一章)Thermal_Design_of_Electronic_Equipment教材.pdf

Hibbeler R. C. “Force-System Resultants and Equilibrium”
Thermal Design of Electronic Equipment.
Ed. Ralph Remsburg
Boca Raton: CRC Press LLC, 2001
0082-01 Page 1 Wednesday, August 23, 2000 9:51 AM
Introduction to Thermal
1 Design of Electronic
Equipment
INTRODUCTION TO THE MODES OF HEAT
TRANSFER IN ELECTRONIC EQUIPMENT
Electronic devices produce heat as a by-product of normal operation. When electrical
current flows through a semiconductor or a passive device, a portion of the power is
dissipated as heat energy. Besides the damage that excess heat can cause, it also
increases the movement of free electrons in a semiconductor, which can cause an
increase in signal noise. The primary focus of this book is to examine various ways
to reduce the temperature of a semiconductor, or group of semiconductors. If we do
not allow the heat to dissipate, the device junction temperature will exceed the
maximum safe operating temperature specified by the manufacturer. When a device
exceeds the specified temperature, semiconductor performance, life, and reliability
are tremendously reduced, as shown in Figure . The basic objective, then, is to
hold the junction temperature below the maximum temperature specified by the
semiconductor manufacturer.
Nature transfers heat in three ways, convection, conduction, and radiation. We
will explore these in greater detail in subsequent chapters, but a simple definition
of each is appropriate at this stage.
CONVECTION
Convection is bination of the bulk transportation and mixing of macroscopic
parts of hot and cold fluid elements, heat conduction within the coolant media, and
energy storage. Convection can be due to the expansion of the coolant media in
contact with the device. This is called free convection, or natural convection. Con-
vection can also be due to other forces, such as a fan or pump forcing the coolant
media into motion. The basic relationship of convection from