Thermal Systems Definitions And Basic Concepts; Thermal Systems Definitions; Thermal Systems Study; Figure 1. Analogy Between Electrical And Thermal System Domains - ST STM32 Application Note

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Thermal systems definitions and basic concepts

This section details basic definitions and concepts related to thermal systems, as applied to silicon-based
integrated circuits (ICs).
2.1

Thermal systems definitions

Heat:
The amount of energy exchanged between two different bodies spontaneously under the effect of their different
temperatures.
Temperature:
A comparative measurement of how much a body is hot or cold. The temperature of a given body increases as it
absorbs heat and decreases as it releases heat out.
Temperature gradient:
Refer to the uneven temperature distribution over one body. The temperature gradient magnitude reflects the
difference in temperature from one location to another inside a body.
Thermal resistance:
The property of a material to conduct a certain amount of heat under a certain temperature gradient.
2.2

Thermal systems study

Thermal systems are designed with complex thermal models and advanced simulation software tools. These
models and tools are used to obtain accurate results.
To resolve a thermal system with an acceptable accuracy and with limited computation effort, many simplifying
hypotheses can be considered (such as considering the thermal resistance to be temperature independent).
Considering these hypotheses, the study of thermal systems is close to the study of electrical systems, where the
heat is equivalent to the electrical current, the temperature is equivalent to the voltage and the thermal resistance
is equivalent to the electrical resistance.
V
A
V
V
B
This model is widely accepted by the electronics industry. Most semiconductor vendors provide thermal resistance
parameters of their packaged products based on this simplified model in accordance with certain standardization
bodies (like JEDEC EIA/JESD 51-X) standards. Most electronics designers consider the provided thermal
resistance parameters when dealing with heat dissipation in their application, or at least at an earlier stage when
selecting the right package for a given product.
AN5036 - Rev 3
Figure 1. Analogy between electrical and thermal system domains
Electrical
system domain
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AB
AB
Thermal systems definitions and basic concepts
Thermal
system domain
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AB
AN5036
T
A
T
B
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