Design for Thermal Issues

Module overview

The aim

All electronic systems dissipate at least some electrical energy which is converted into heat, and modern circuits operating at ever-increasing frequencies dissipate an increasing amount of heat, usually within a smaller and smaller enclosure. This has meant that, over the past twenty years, designing for thermal issues has become the concern of many within the electronics community, and not just limited to those whose products work in hostile environments. So, for many students, learning about thermal design, and gaining experience of the simulation software used, will be essential elements in their Continuing Professional Development.

As explained in the Module Descriptor, what we are seeking to do in this module is to allow you to explore the issues at component, board and system level, and show how appropriate modelling of the thermal aspects of a design can enhance the performance and reliability of a product. Our approach is to concentrate on practical solutions and present analysis methods with the minimum of mathematics. However, some calculation is inevitable, and it will be necessary to gain an appreciation of the methods that are used to solve the complex equations created to simulate the physical world.

Exercise

The module is grounded in real applications and realistic methods, and we would encourage you to spend 20 minutes listening to the presentation at this link. The original paper that we comment on describes an application of simulation software to a thermally-demanding state-of-the-art application. The presentation will highlight the issues, illustrate the modelling challenges and the approach taken, and give you a flavour of what you will understand as a result of your studies of this module.

 

How the module is structured

Figure 1 shows the module contents in diagrammatic form. The first four units seek to answer the kinds of question: “How big is the thermal problem?”; “Where does the heat come from?”; “What will happen if I don’t remove the heat?”; "How should I set about managing the heat?”. Thereafter, the module texts are split into two topic areas, and presented in parallel, because you should aim to make progress in your thinking on both:

Supplementing these, and shown in the right-hand column, are tutorials and activities that relate to the specific software that we are using in this module. The diagram also shows the approximate positioning of the assignments within the main flow of topics.

The light blue boxes are for units that contain learning material on the background theory and thermal management practice; the green boxes are the units with an emphasis on materials and the practicalities of implementing thermal management; both have the usual activities and Self-Assessment Questions. The pink boxes are for units that deal with modelling, and give background to the software-based activities and tutorials, including the two assignments.

In some cases, there are specific links across, for example, in the way that Unit 10 provides specific information on component structure that will help you to understand Unit 12. Similarly, when you model at an enclosure level, you will need to understand some of the practical factors that apply to fans and enclosures as described in Units 15 and 16. Bear in mind that the assignments require you both to model and to reflect on the result of your modelling, so you should not expect to succeed in this module if you fail to study these peripheral units.

Although you can dip into the materials, our suggestion is that, following your study of Units 1 to 4, you should work your way systematically through the units in numerical sequence, which will automatically interleave simulation and materials topics, and give you some respite from detailed analysis and the use of software!

Figure 1: General arrangement of the module

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In an ideal world we would give you experience with a range of software, making the course vendor-neutral. However, we realise that to do this would mean your spending overmuch time on learning to drive the software, to the detriment of your study of the underlying theory and your application of the software to representative tasks.

For this reason we have chosen to work with a suite of software which is one of the market leaders in the area, and can be applied at component, board and system level. However, we have taken pains to explain how the software compares with other packages, and in particular how you might use more simplistic approaches both to give an essential “sanity check” to the results of simulations and for applications where full simulation software is not available.

This is fully-functional proprietary software, provided for educational use, and made available to you through the Bolton server, as with the design software used on other modules. To access this you will need to load the appropriate Citrix client on your computer, and have internet access during your work on the software; more details in Unit 11 and on the Practicals index page. Note that, whilst broad-band access is a help for any web-based learning, it is not essential for this module.

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Studying the module

As indicated in the timetable below, many of the topics are grouped, reinforcing the message that units are not the usual nominal 8–10 hours: some are really quite short; others considerably longer, especially Units 9 and 11, because of the need to go through the tutorials and make use of the software. You will probably find it beneficial to go through the other text-based units more than once, and we suggest an initial skim-read, followed by work on the software, returning to the written material in more detail before completing your practical and assignment work.

Whilst the timetable is not “set in tablets of stone”, and two weeks slippage is allowed for holidays and similar, we would strongly advise that you attempt to keep to this timetable, in particular making an early start on the work with simulation software, so that any problems can be ironed out as they arise without jeopardising the final outcome.

Study Week Unit Unit / Assessment
1 & 2 1
2
3
4
The need for thermal management
Sources of heat
The effects of heat
Managing thermal design
3 5
6
7
Mechanisms of heat transfer
Thermal properties of materials
Making thermal measurements l
4 & 5 8
9
Thermal modelling basics
Simplified methods using computation
6, 7 & 8 10
11
12
Ass.1
Thermal paths in components
Approaches using simulation software
Modelling components
Modelling at the board level
9 13
14
Removing heat through the board
Choosing a heat sink
10 15
16
Practical aspects of fans
Practical aspects of enclosures
11 & 12 17
Ass.2
Applications of thermal management
Modelling heat at the system level

Accessing the module content

The module content may be accessed from the hot links on Figure 1, from the drop-down menu, or from the list of contents below. We have replaced the previous map that showed the whole module with lists at the bottom of each unit text that identify all the key elements and links. You may find this helpful as a check that you have found all the materials, or when you are going away on business and need to download/print information in advance.

Resources

Software

A number of software resources are available to support your studies, and we have written appropriate introductions to these. You will make use of FLO/PCB during your studies from Unit 9 onwards, FLOPACK appears in Unit 12 and you will need FLOTHERM for both assignments.

Both FLO/PCB and FLOTHERM have tutorial material which we strongly recommend you to go through in detail before starting to use either of the tools. The FLO/PCB introduction refers to a set of Flomerics tutorials, while the walkthroughs for FLOTHERM have been written by the module team.

Web-based material

For both teaching purposes and practical reasons of page length, the main text for many units has a number of linked resources that are either an integral part of the unit, or else give supporting detail. We recommend that you look at all of these, if only to check that you are aware of the topic in sufficient depth.

The module also makes references to a number of web-based resources; we found the electronic archive of the Electronics Cooling magazine particularly useful. We have selected relatively stable sites, but please contact us if you find that key materials have disappeared, and we will provide you with access to back-up sources or equivalents.

Where we have linked to external materials, we would encourage you to look at most of those resources, rather than just skip over them. Whilst their value varies, there is usually some insight to be gained, and often the sites chosen have visual material that is not directly available for us to incorporate in this module. Certain units in particular have a number of such links, some of which are more important than others, and we have indicated which items are key in the lists at the end of each unit.

As part of your studies we hope that you will make use of other web-based resources, and you will probably need to do this as part of the assignments. However, be careful to assess the validity of information you uncover, and resist the temptation merely to collect vast swathes of data.

Health warning!

When you look for information on the web, using search engines, we always recommend a degree of caution; it is very easy to get an unbalanced view, and easier still to get swamped. So, before you start, please read our note on using web resources.

 

Books

This module is intended to be self-standing as far as possible, but a considerable amount of material on thermal issues is available, and we have described a selection of the books and journals that we consulted during the course of preparing this module in the list of resources at this link. We have a bias towards practical understanding, as will be evident from the comments, and have therefore suggested no books for general reading.

There is, however, one book that you may actually enjoy reading! This is Tony Kordyban’s Hot Air Rises and Heat Sinks. Written in his inimitable style, this contains a number of case studies – an imaginary company and personnel, but extremely realistic nonetheless. This book will enhance your understanding of the subject, and help you to make correct design decisions, although it is not in sufficient detail to help you tackle the assignments!

Additional support

Depending on the nature of your work and the subjects you have studied, you may need additional help; a good starting point is this list of topics, which links to a range of relevant short papers, primarily on materials and reliability issues, not all of which are referenced in the module texts.

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Assignments

There are two assignments for submission in Weeks 8 and 12:

For both assignments you will be expected to reflect on the learning experience and on the thermal challenges of the board/system, relating these to good practice, with the record of the practical work you have undertaken as a supplement to your report.

As well as providing an introduction to simulation software, with some simple illustrations based on one of the software tools, Unit 11 also contains an introduction to the assignment work.

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Contributors

The module authors would like to acknowledge the considerable contribution given to the revision of this module by the early cohorts of students, especially Sarah Thompson, who articulated the unasked questions of many others, and Chris Hill, whose understanding of the issues created both model assignments and some examples that we have been able to incorporate in our revision.

Author/tutor profiles

""Murray MacCallum is a senior lecturer at Napier University in Edinburgh, where he has been a member of staff in the School of Engineering for over 20 years. During that time he has taught on a wide variety of courses, from general electronics to more specialist subjects like PCB manufacture and CAD. He has also supervised many projects at both undergraduate and postgraduate level.

Murray has designed and delivered a range of short and longer-term training courses for industry, concentrating mostly on electronics manufacture. He is a qualified instructor with the US PCB authority, the IPC. He has also engaged in a number of consultancy projects, most notably the design and installation PCB prototyping laboratory in Sri Lanka.

Murray is responsible for the software-based activities and assignments in this module, and is the author of the unit material on software and simulation issues (mostly in Units 8 and 11).

Martin Tarr is a specialist consultant engaged to author and tutor this module. He provides technical and marketing services to many companies in the electronics industry and also teaches with Napier University at the Scottish Advanced Manufacturing Centre. His area of interest covers all aspects of interconnect technology from semiconductor back-end processes through to equipment practice.

In his 40 years in the electronics industry, Martin has learnt the hard way how components are made and assembled into boards and systems, and how failure can occur both under adverse environmental conditions and what appears to be normal operation.

He has been intimately involved with custom applications of a wide range of technologies from valves to multi-chip modules, and in industries from avionics to heart pacemakers to industrial process control. In recent years, he has combined his technical/marketing consultancy with a commitment to teaching and has qualified as a registered practitioner of The Higher Education Academy.

Martin is responsible for all aspects of the module texts except those on software and simulation issues.

 

 

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