THERMAL DESIGN

THERMAL MANAGEMENT OF ELECTRONICS, HEAT EXCHANGERS GUIDES, FREE SOFTWARE AND CALCULATORS

Technically speaking,

temperature

is a measure of the average molecular kinetic energy in the matter. The normal flow of kinetic energy is from a higher temperature region (or an object) toward a lower temperature region (or an object). This flow is referred to as heat transfer. In general, there are three types of heat transfer: conduction, convection, and radiation. Conduction is the collisional transfer of energy between atoms, which occurs in solids. Convection is the motion of molecules in air or fluids. Radiation is the energy flow by electromagnetic waves. In practical electronics only the first two types are noticeable.

Electric currents or alternating electromagnetic fields cause power dissipation in all electronic components, which results in increase of their temperature. The reliability and life expectancy of any component is related to its operating temperature. Failure rate and its inverse, mean time between failures (MTBF), are measures of the electronic system reliability. According to Arrhenius model, each 10°C rise in temperature increases the failure rate by 50%. At certain temperature any electronic component can be irreversibly destroyed (a typical maximum operating temperatures for semiconductors is 125-175 C at the junction, capacitors 85-125 C, wire insulation- 105-200 C). The thermal management and engineering whose task is to control the operating temperature of the product, is therefore an essential part of electronics design.

When designing a heat sink for a component cooling, you first need to choose a maximum operating junction temperature Tjmax (typically, 105-120 ^oC for semiconductors). Then for convection cooling the required heatsink thermal resistance should be
R_th-hs<(Tjmax-Ta)/P-(R_thj-c+R_thc-hs) ^oC/W,

where Ta- ambient temperature, R_thj-c - thermal resistance between junction and the case from the datasheet (typically 0.5-2.5 ^oC/W for conventional power packages), R_thc-hs- thermal resistance between the device's case and the heatsink, P- power dissipated by the device in watts. Based on a "rule of thumb" calculation formula found empirically by Harry Lythall, the required aluminum heat sink's surface area in sq.cm is A=(50/Rth-hs)². The main optimization criteria are to maximize the exposed heat exchanger's surface area, and to minimize its weight and the mean distance of the exposed surface from the component to be cooled.
Below you will find free calculators and more information on the thermal design.

HEAT AND THERMODYNAMICS BASICS

THERMAL MODELING AND ANALYSIS SOFTWARE

THERMAL DESIGN GUIDES, ANALYSIS & APPLICATION NOTES

Heat conduction formulas

Heat Radiation

A heat transfer textbook for engineering students (conduction, convection, radiation)

The First Law of thermodynamics

PCB LAYOUT DESIGN GUIDELINES

FIND HEAT MANAGEMENT PRODUCTS BY SPEC

ThermoAnalytics demo software

Thermal conductivity units

Temperature units conversion

Flow velocity calculator

Thermal resistance and fin efficiency online calculators

THERMAL DATA OF ELECTRONIC COMPONENTS

Basic thermal management of semiconductors

How to determine thermal resistance for a power semiconductor heat sink

Materials thermal conductivity

Heatsink extrusion temperature and length correction

Fan speed controllers designs

What you need to know about cooling fans

HEATSINK PROPERTIES AND DESIGN NOTES

How to select an extruded heat sink

Analytical Model for simulating electronic systems' thermal behavior

Heatsink design guide

CUSTOM POWER ELECTRONICS SEARCH ENGINE