Thermal architecture design for electronic products is very similar to solving a high-level puzzle

High temperatures lower not only the lifetime but also the performance of many electronics. A clever, cost-effective thermal design translates into a commercial advantage. ‘Your competitive edge increases  if you can deliver performance at lower costs or offer more performance at the same price through better cooling’, says Wendy Luiten, who delivers the Electronics cooling thermal design training.

High Temperature impacts the performance of everything that depends on computing power or memory. It is also an important factor for the performance of image sensors and energy converters, lamps and power supplies.
One of the difficulties in thermal design is that key decisions often go unnoticed. Says Luiten: ‘If you want to do it low cost, many critical cooling parts are not directly visible. They do not show up on your Bill of Materials. That makes it tricky. Passive fan-less air cooling is a preferred low-cost cooling solution, but air is not on your BOM. Neither are the open spaces that accommodate air flow. So, if a mechanical designer incorporates an open space as an air path in the design, it is not registered anywhere by default as a cooling component. That means that at a later time in the design process changes can be made that disable the original cooling concept. It is just not in the documentation, if you don’t put it in specifically.’

Don’t design tools to take this into account?
‘No, not really. Thermal behaviour is the combined result of electronical and mechanical design and the effect of a change on cooling performance will show up in CFD (Computational Fluid Dynamics) Thermal simulations that combine the inputs of both. But it will not show up in stand-alone Electrical and Mechanical design tools. You often see in product development that a thermal simulation is ran based on the finalized mechanical CAD and electronical layout EDA files, but essentially then what you have done is replacing the hardware prototype with a CFD simulation, after the detailed mechanical and electronical implementation has been finished. If the thermal simulation shows a problem with temperature, part of the mechanical or electronical design process has to be re-done. Obviously, that is a waste that you want to avoid.’

How does your training offer a handle on this?
‘We teach a way of working as well as the physics. Thermal design needs to be taken into account starting in the architectural phase and thermal risks addressed pro-actively. If you think the IC might need a heatsink, address the issue and ask the layout to put in heatsink mounting holes.  Do not wait until the complete lay-out is finished and you can do a test.  If layout has just completed a complicated multi- layer board, and part of it has to be re-done in order to accommodate the mounting holes for the heatsink, people are not going to be happy’. ‘So, if you think there is a risk, ask for the holes.  Maybe they are not needed after all, but unused holes in the PCB are no big deal. The other way around carries a much larger project risk: if you do need the heatsink but the holes are not included, the layout will need to be party re-done, and that can cause a development time delay’. ‘With a good thermal design, a lot is possible, but you have to make sure that the thermal concept is sound from the beginning of development to avoid re-designs.’

High temperatures have a negative influence on the life expectancy and reliability of components. Therefore, some chip manufacturers integrate temperature control software in their IC’s. Intel started by incorporating a thermal sensor in its P6-processors that simply shut them down if they heated up too much. Intel’s Pentium 4, Xeon and Pentium M processors had an additional over-temperature protection that slowed down the IC’s clock speed if it got too hot.

But temperature safeguards don’t automatically have a positive influence on the thermal behavior, indicates Luiten. ‘Many people think that using an IC with temperature protection solves the thermal problem, but this is not the case. The safeguard does not cool the IC but typically lowers its energy consumption by lowering the performance.  If the products thermal design is weak at system level the component will get hot sooner and more often and the end performance at system level will be jeopardised.’

Luiten found this out first-hand in a recent consultancy job on an image processing device. As soon as the video processor became too hot, the display went black. ‘It turned out to be an intended feature, not a bug. The video processor had embedded memory that was susceptible to high temperatures so the component supplier had added a temperature protection. As soon as the internal temperature sensor experienced over-temperature, the thermal protection kicked in. Normally this would not have been a problem, but in this case the product was developed for use at higher temperatures so the black screen was an unpleasant surprise.’

Because of this components temperature protection, the thermal design of the product became more critical. ‘If the IC’s temperature went up too high, it switched off. So, the protection seemed like a clever thing to do at component level, but at the same time it made thermal design more critical at the system level. In the end a partial re-design was needed to make sure the product worked way as intended.’

What is the most important topic in the training?
‘Thermal problem solving and better cooling design. Heat is a major performance-limiter in many electronic systems, from computers to lighting. The moment you can cool your product better at the same price point, this translates to better performance at the same price and this is a commercial advantage.’

Where do attendees work?
‘We have people attending from all levels in the system design, from component to module to complete system. Many former attendees worked on components, small electronic products and LED applications, but we have also had people working on large systems, like radar systems or heat sinks in large power supplies and we have had people from cooling component suppliers. With the increase in automotive electronics we also see more people coming in from that field.’

What makes people sign up?
‘Part of them come by word of mouth. Clemens Lasance and myself are both known in the international electronics cooling community and so is this thermal training.  The training is in English and draws an international public. We have had people coming in from as far as the United States that had heard they had to go to Eindhoven in order to get a really good thermal training.’

What makes the training special?
‘Clemens and I really teach electronics cooling in an application-oriented way. The training covers all aspects and is very hands on: we go from high level system architecture to implementation level details such as layout and locations and dimensions of air vents. And this is backed up with physics and best practices.

You don’t learn how to swim by just looking at other swimmers. Our goal is to send participants home with applicable skills, and that includes the hands-on ability to do basic calculations.’

‘I want people to get a sense of sizing, to get a gut feeling for thermal estimations.  If you have this ability, you will be able to take much better design decisions and you will also be much more confident in doing thermal simulations because you better know what is happening.’

Can you bring your own case study?
‘We always ask participants beforehand if they have a case of their own to share. If applicable, we will discuss it during the training. This is fun, because it leads to lively discussions. In addition, we have some standard cases.’

During the training: learn to thermally interpret specifications

Lasance and Luiten discuss the physics of electronics cooling, how to benefit from best practice thermal ways of working and how to implement them during the product development phases. This also explains why time management and project management are part of the course. ‘We discuss specifications and the way to interpret them thermally as well. We have people from system, sub-system and component level – this leads to interesting discussions on the interpretation of specifications.’ ‘The last learning activity of the course is a case study.  We split the group into two teams and spend two to three hours to crack a case. This is an eye opener to many people because it is the first time that they take the factors and specifications at all levels into account and see for the first time how mechanical and electronic considerations interact into the thermal behavior from component to system.’

When you have finished the training…
‘You have applicable skills on estimating thermal effects that you can use to estimate how to cool a product properly. Many participants indicate that this is the unique selling point of our training. Both people that are new to the field and experienced thermal architects and designers comment on how much they have learned during our course and recommend it to their colleagues. In addition, the know-how increases confidence in your results if you happen to do thermal simulations because you better know what you are doing.’

What people attend?
‘Attendees typically have higher education in a technical field such as electronic engineering, mechanical engineering, physics, optics, or industrial design. We often see product developers and architects with a couple of years development experience get into the thermal discipline. In Europe we have no higher professional education or academic education in this field. The United States do have universities that offer cooling of electronics courses, but they have a more academic approach.

Do you update the course regularly?
‘Absolutely. Recently we decided to split the training and you can choose either to go more in-depth with Clemens Lasance or do more hands-on exercises with me. That change was well received. At the moment, I am working on Design for 6-sigma and thermal design. In the thermal architectural phase, you already have to check how mechanics and electronics work together, identify the demands on the thermal behavior and design, optimize and verify how to make it work out. This combines well because of the system level approach in DfSS. And you can get great results in design and optimize phase with the combination of computer CFD simulations and Design of Experiments.’

Photo by: Bart van Overbeeke

Wendy Luiten started her career halfway the 80s as a thermal specialist at the Philips Centre for Fabrication techniques, at that time just split from the well-known Philips Research Laboratory (Natlab). In the late nineties, she contributed as a thermal architect in the development team to the first flat-screen televisions, made by Philips Consumer Electronics. ‘These early plasma screens had fans on board, and the fan noise was not liked so the challenge was to take them out.’ Luiten wrote a paper on the thermal design of the first plasma TV in the world without fans. This won her the best paper award on the Semi-Therm conference.

Cooling of electronics in consumer TV at first was seen as a temporary phenomenon. Managers assumed that existing heat problems would not be there forever. In reality, whenever a generation of televisions had outgrown its heat problems, product managers would pile on new demands on the development teams, going from plasma to LCD screens, the rise of HD TV, LED TV, 3D TV and smart-TV.

‘Every new generation would have its heat problems’, Luiten says. She ended up working sixteen years on a temporary problem. She is laughing about it. ‘I have done a temporary, non-structural activity for sixteen years straight.’

Since 2000, Luiten teaches courses Cooling of electronics. She has been all over the world for this, travelling to China, Singapore, Taiwan, Korea, the United States and several countries in Europe. Luiten also has been teaching in Saudi Arabia, at a summer school in Turkey and last year she presented the pre-conference short course Fundamentals of thermal system design at the European Therminic conference.

Together with Clemens Lasance, Luiten has been teaching the workshop Thermal design and cooling of electronics for fifteen years. This particular training has been split up into two modules and is being held online and Eindhoven, but the two of them were also presenting a pre-conference short course at the Semi-Therm conference in the United States. The combination of Luiten’s years of electronic product development experience and Lasance’s broad and deep knowledge of their discipline works particularly well. This marks their training as distinctly different from other available courses around the world.

Luiten is passionate about her subject, because she loves solving puzzles. ‘Designing the right cooling architecture for a range of TV’s forming a certain generation is similar to high-level puzzling. Together with the electrical and mechanical architect, you have to cover as many models as you can with the smallest set of different components. You need a flexible and scalable cooling strategy to cover the product diversity at acceptable cost.’

Nowadays Luiten is principal of her own firm: Wendy Luiten consultancy. ‘Not quite an original name, but highly practical.’

Getting the thermal design right for the Internet of Things

Thermal aspects are only part of the total problem, but Luiten expects the significance to continue. ‘Electronics cooling is important in the energy transition. Converting solar and wind energy to the grid requires power electronics, and this has thermal limitations. In addition, the materials that convert light to electricity and vice versa also are known to be temperature sensitive.’ ‘The transition to electrical and self-driving cars is also a hot item. Currently electronics make up 30 percent of the total costs for a car, and that is rising.’

Says Luiten: ‘Automotive electronics can be safety critical, failure for thermal or other reasons is not acceptable.’

Meanwhile in data communication, cooling is a well know cost issue ‘Data center cooling can cost as much as processing data, and in telecom 5G is expected to be a thermal challenge as well. For the Internet of Things also, getting the thermal design right is important. In future, there will be sensors everywhere.’

Partnership High Tech Institute

The training Cooling of Electronics is part of the T2Prof portfolio. T2Prof has continued the technical trainings on electronics and optics originally developed at the Philips Centre for Technical Training. T2Prof brings its courses on the market in exclusive cooperation with its partner High Tech Institute. High Tech Institute focuses on the marketing, sales and organization of these courses.

This article is written by René Raaijmakers, tech editor of Bits&Chips.