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Sensible Design: Thermal Management—Good Design Practice for Heat Dissipation

Trial and error is an essential process in the development of new and innovative products, however, excessive testing can be unnecessary and costly. Incorporating thermal management at the preliminary stage of your design process will ultimately lead to more reliable and cost-effective end products. As a matter of good practice, evaluating thermal performance in all phases of the design cycle will also confirm any issues early on and help to prevent a costly system-level teardown.

This month, I’ll be exploring thermal management tips for effective heat dissipation at the design stage as well as examining helpful tools to protect your electronic circuitry. Let’s explore some of these key areas in more detail and discuss good design practices that ensure better thermal management.

Good Design Practice
The following list contains some of the key factors. How important are these and are there additional ones?

• Performance data and dimensions of the components
• Major heat-dissipating components
• Size of the PCB
• PCB material, layout, and component placement
• Mounting peripherals
• Temperature of the application environment
• Amount of heat dissipated
• Appropriate cooling methods, i.e., cooling fans, heat sink, etc.

All the above points could influence the efficiency of the design produced and there are arguments for the importance of each one. In my opinion, you can separate these out into two categories, with high priority items including the correct choice of materials, the overall layout of the PCB, and the temperature of the surrounding environment. Factors such as the overall size of the PCB, the amount of heat dissipated, and the mounting peripherals are perhaps less important because they will all be dependent on the design; in some cases, they may have a large impact and in others, a negligible effect. The main point is that none of these factors should be considered alone. To achieve good thermal management, a holistic approach must be taken with suitable thermal analysis to ensure the best overall performance is being achieved.

Identifying Components
Is it possible to identify components with the potential to dissipate more heat and factor this into the design process?

By reviewing the power consumption of components, you may get an indication as to the potential heat generation of a component, but this is not an ideal method to use. Each PCB will be designed differently and have an array of components. It is how these components interact with one another and how heat can flow through the assembly that should be considered in detail during the design phase. For example, heat-sensitive components should not be placed next to components with high heat generation. Components with higher power consumption should be placed near heat-dissipating technologies. Wherever possible, a relatively even heat distribution should be maintained rather than having “hot” and “cold” areas of the board. Using heat dissipating technologies, such as thermal interface materials, can assist in achieving this successfully.

Thermal Analysis Tools
What thermal analysis tools exist to identify thermal problems with a PCB?

At a basic level, thermocouples can be used to measure the temperature of specific components or areas of a PCB. More recent technologies consider the use of heat flow sensors to show the movements of thermal energy throughout the board and specifically through components. They can be used to show the generation of heat by a specific component, and the ability of the component to absorb heat generated by an external source. Thermal imaging can be used in a similar way to show the various temperatures across PCBs. Infrared cameras also carry out thermal imaging of the board and individual components. They can give a clear view on where heat is gathering within the device and help to show where additional heat dissipation may be required.

Removing Heat
What are the most common methods to remove heat from circuit boards? 

Heat dissipation can be achieved in a number of ways. As we have already discussed, the design of the PCB can help to manage the heat flow across the board and ensure successful heat dissipation. Where heat generating components are present, a heat sink and thermal interface material may be effectively utilised. In addition, if thermal analysis shows that there are still areas of the PCB where heat may be gathering, thermal gap-filling compounds may offer additional heat dissipation. In other technologies, forced air flow and fluid cooling may also be used, however, these may not be suitable for all devices as they may require extra space or technology to successfully implement. This again shows the flexibility of thermal management compounds that can be used at the interface of a component and heat sink device, thus improving heat dissipation from the source.

Heat dissipation in compact electronic assemblies is a vital design issue, which, if not fully appraised at the design stage, could cause premature product failure and loss of supplier reputation. Most electronic components are low power and produce negligible amounts of heat in their operation, however some devices, such as LEDs, power transistors, CPUs, and power diodes produce a significant amount of heat. Failure to effectively dissipate this heat away from the component or device can also lead to reliability concerns and reduced operational lifetimes. Sufficiently implementing thermal management at the early design phase and evaluating it from concept to manufacturing will create reliable devices with an extended life expectancy. There’s a lot to consider when selecting the appropriate thermal management material, however, our technical support team can help designers find the right solution for specific heat transfer challenges. I hope this column has been useful and of course, we are always happy to help and advise. In the meantime, watch for my next column on thermal management.

This column originally appeared in the June 2021 issue of Design007 Magazine.