An explanation of the basics of "heat dissipation design" and how to apply it to electronic devices

Some of the electronic components that are used in electronic devices become quite hot during their operation. Therefore, it is essential to consider heat dissipation design stage for these devices.

Some of the electronic components that are used in electronic devices become quite hot during their operation. As their temperature increases, not only will the heat have an effect on the operation (characteristics) of the electronic components themselves, but the heat transmitted through the electronic board may also affect the operation of other components, or the heat may cause the electronic components or the board to become warped, destroying circuits, or cause burns to a user, or even ignite a fire, resulting in a dire accident. Therefore, it is essential to consider heat dissipation design for these devices.

• Heat Dissipation for Electronic Circuits
• Concepts of Heat Dissipation Management
• Vapor Chambers: Thin, Light, and Superior Heat Dissipation Performance
• DNP’s Vapor Chambers

On an electronic board where electronic components are mounted, how is the heat generated by a given component dissipated (transferred)? There are 3 types of heat dissipation. The first type is “thermal conduction”, which refers to the transfer of heat from electronic components to the relatively lower temperature electronic board through the parts of them that make contact with each other such as leads and solder. The second type is “convective heat transfer”, which refers to the transfer of heat into the air. The third type is “thermal radiation”, which refers to thermal energy being emitted from the surface of electronic components as electromagnetic waves (infrared rays).

Of these 3 types of heat dissipation in electronic devices, thermal radiation is generally so low as to be negligible, and it is usually not taken into consideration. Contact with air is important for heat dissipation through heat transfer. The larger the area exposed to air, and the more air flowing through the area, the more advantageous it is for this process, but for smaller electronic devices, this does not result in much heat dissipation. For electronic components, especially smaller ones, thermal conduction, the transfer of heat into the board or substrate, accounts for the majority of the heat dissipation.

The electronic components of devices in the past were laid out on the boards with plenty of room so there wasn’t too much of a need to consider measures to mitigate the heat of those components at the design stage, with the exception of those that generated an exceptional amount of heat. Now that electronic devices have progressed to become smaller and more advanced and their electronic components have also become smaller and have increased in density of placement, it is now absolutely essential to consider heat dissipation from the design stage (Heat dissipation design, Thermal design).

Heat dissipation management involves defining the upper temperature limits at which each electronic component operates normally. When defining these limits, it is necessary to consider both the ambient temperature of the operating environment as well as the surface temperature of the electronic device. Additionally, it also is important to keep in mind that components that dissipate small amounts of heat may actually gain heat due to the heat dissipated through the board or substrate by other components that dissipate their own heat.

Next, one must conduct a thermal analysis (simulation) based on the thermal generation and conduction characteristic data of the electronic components and the board or substrate on which they will be mounted so as to confirm that the previously defined upper temperature limits are not exceeded. Careful attention must be paid to microprocessors and power supply related components in particular as they generate a lot of heat. If the analysis results are indicative of the upper temperature limits being exceeded, the thermal analysis will be repeated with the inclusion of measures to keep the temperature under the limits such as alterations in the placement of components or parts, the addition of heat dissipation components (heat sinks, heat pipes, Vapor Chambers, fans, etc.), or alterations in the materials or shape of the equipment chassis.

Examples of thermal mitigation measures considered in heat dissipation management can include placing components that generate more heat away from those with a lower level of heat resistance, and placing components that generate heat downwind of the airflow within the chassis so as to let cooler air pass through. In addition, there are other methods that can be employed to further dissipate the heat that was transferred to the board or substrate onto the chassis such as reconfiguring or increasing the locations where the board is fixed to the chassis, changing the materials from which the contacting parts are made, or changing the materials used in the chassis itself.

What’s even more effective in dissipating heat is to employ components used specifically for heat dissipation separate from the board itself. Heat dissipation components used for small electronic devices include small fans, heat sinks, graphite sheets, heat pipes, and Vapor Chambers. Each of them have their own advantages and disadvantages, but heat pipes and Vapor Chambers are said to have an excellent ability to transfer heat (to move heat energy from higher temperature areas to lower temperature areas).

Graphite sheets are thing, light heat dissipation components with a high degree of thermal conductivity, but a special characteristic of Vapor Chambers is that they possess a thermal conductivity several times higher while being almost as thin and light. Heat pipes are similarly comparable in terms of their high thermal conductivity, but the fact that they incorporate metal pipes means that they are challenging to implement in tight spaces, and their relatively heavy weight makes them difficult to use in small electronic devices.

Vapor Chambers are thin sheet-like heat dissipation components made of metal. They have very high thermal conductivity and their operating principle is the same as that of heat pipes. Generally, Vapor Chambers that employ meshes have a fine capillary structure (wick) contained inside that is filled with a working fluid such as pure water. The internal capillary structure of DNP’s Vapor Chamber, on the other hand, is characterized by having a form that is made to be extremely fine and precise by means of using etching technology. When one end of a Vapor Chamber is situated to be in contact with a heat source, its working fluid evaporates, absorbing latent heat in the process, and the resulting vapor moves to a lower temperature area where it releases the heat and returns to liquid form. This working fluid returns to the heat source through the wick by the process of capillary action. This cycle is very short and continuous, and requires not external power.

DNP, using in-house ultrafine precision metal processing technology, has developed a Vapor Chamber with a thickness of 0.20mm, comparable to that of thermally conductive sheets. It is also flexible to some extent and can be applied to curved or graded surfaces. （Information as at Feburary,2022）