Thought Leadership

An Interview With… Clemens Lasance

By Robin Bornoff

Every industry or industry sub-sector has its movers and shakers, its pioneers and thought leaders. These people have likely helped shape and evolve that industry to what it is today and what it may become in the future. For this series of ‘An Interview With…’ blog posts I will be posing the same set of questions to leading lights in the electronics cooling community to get their views on various thermal topics. Actually the last question is who to address the questions to next, in that way I hope a self sustaining chain can be set-up (here’s hoping it lasts more than one link!).

My first business trip abroad with Flomerics back in 1996 was to Philips in Eindhoven with one of the founders of Flomerics, Harvey Rosten. We visited Clemens Lasance and his colleagues to discuss FloTHERM and its use in Philips, one of a number of regular visits that proceed to this day. In this context Clemens kindly agreed to be the first in the chain. First his bio, then the questions and answers:

pasfoto_clemens_s2Clemens Lasance, retired in September 2009, was a Principal Scientist at Philips Research in Eindhoven, the Netherlands. He has been on the Philips staff since 1969, after he received his physics degree at EindhovenTechnical University. From 1984 onwards, his main focus has been thermal management of electronic systems. In 1996, he moved to Research, engaged with a long-term research program in this field. He published over 80 conference and journal papers. Both in 1995 and 2009 he (as the leading author) received the Best Paper Award at Semitherm. He is an editor of Electroinc Cooling magazine since its launch in 1995 and of Microelectronics Reliability. From 2000 to 2002, he led a successful EC-funded ten-partner consortium project called PROFIT resulting in 85 papers and 60 deliverables. He received the SEMITHERM Significant Contributor Award in 2001. He was the General Chair of SEMITHERM 2003 and acted as the co-program chair of THERMINIC for nine years. In 2006 he was the recipient of the Harvey Rosten Award for recognition of his pioneering contributions to thermal management issues over the past two decades.

1) Where do you see the biggest changes to the electronics cooling industry coming from?

I expect the biggest changes will be driven by the lighting industry, by the booming business of LED driven applications. These will affect a lot of industries that originally were not much interested in thermal management. Additionally, the LED industry is focused on lifetime. As an example, the Department of Energy (DoE) in the US swore not to make the same mistake as they did with the introduction of the energy-saving lamps in the early eighties. They didn’t make it because the promised lifetime was not realised, partly due to the electronics. We see the same problem nowadays: while the LED itself can easily meet 50000 hours, the rest of the system cannot, especially the electronics and the interface materials. Hence, I expect much more emphasis on the relation between temperature on the one hand, and reliability of parts and system, performance and safety on the other hand. Additionally, because of the long lifetime and the required reliability, testing will become a real problem because of the time required to reach significant conclusions. I expect that henceforth much more research will be put in reliability prediction using physics of failure principles, coupled with dedicated testing to find suitable failure and damage models. Accelerated testing will become something of the past.
Another area that will foster is the data center business. I am sure that in the future it will not be tolerated anymore to put megawatts of waste power into the air. The promising alternative is liquid cooling, and use the hot water for various purposes.

Of course, when the holy grail is found: thermoelectric materials with a much higher efficiency. This will really change a big part of the thermal management world because not only cooling options will change dramatically but also the omni-present temperature differences will generate electricity everywhere. Autonomous devices will rule the world.
Finally, I foresee a lot of work in the area of health care where all kinds of fascinating developments are going on. Many of them require thermal management in one way or another, such as disposable cartridges used for DNA amplification.

2) Do you see the need for electronics thermal management ever disappearing and why?

I don’t think so. Some people had these thoughts way back when changing from TTL to CMOS, but in my experience all electronic designers look for a possibility to get the maximum out of their design. This simply means more power, and this simply means higher temperature. Unless you are in the heating business this usually means problems. One of the ways to overcome high-temperature problems is to control the temperature actively and keep it constant. Then you don’t need to bother about the temperature anymore, but on the other hand, the control circuitry again requires thermal management.

3) What do you consider your most valuable contribution to the electronics cooling industry?

Probably the development of Boundary-Condition-Independent Compact Thermal Models. While the principle was co-developed with the late Harvey Rosten, I was the first who actually realised such a BCI model, around 1994.

4) How should software vendors serving the electronics cooling community change their practices and provided software capabilities to better meet the needs of the industry?

Let’s make a distinction between pre and postprocessors. Starting with preprocessors, my personal observation withthe use of many codes is that somehow the big gap between the person who develops the software and the person who is using the software is not recognised well enough. For developers (and for very experienced users) everything seems logical because every move seems a logical consequence of the former move. This is absolutely not the case for the novice user, or the occasional user. For a developer it is often an impossible task to make a code more ‘logical’, meaning paying attention to the way of working of the average customer. Hence, it is recommendable to ask a person who is familiar with computers and similar packages for comments very early in the design phase. The challenge for this person is to keep the familiar way of working and real ‘logical’ sequences separated. ‘Logical’ is between quotes because it is rather based on a common way of working for many years, like CTRL-C/V. I expect that some of these will become embedded in our genes somewhere in the future. In summary, the way of working of customers is pretty much different from the way of working of developers. Onto postprocessors. I am saying for years that the standard output, namely temperature and velocity fields, are of limited use when it comes to interpretation and, more importantly, directions for improvement. It is not sufficient for a designer to know that something is too hot, what he/she wants is to solve the problem. It is here where the computer may help, and I have a lot of ideas how to adapt the output in such a way designers would love. The new output parameters that Flotherm offers (the Bn and Sc numbers) are for sure a first step in this direction.

5) What question would you have liked me to ask and what would your answer have been?

Does heat transfer teaching at universities meet the demand of industries regarding cooling of electronics?
Posing the question is answering it. Absolutely not. There is a big gap between academic heat transfer and real-life heat transfer. For one, we don’t live in wind tunnels, we rarely are dealing with only one source, we seldom have uniform boundary conditions, the reference temperature of the heat transfer coefficient does not make sense, and we cannot buy some ideal insulation material. I am not arguing that students should not learn basic heat transfer, I am arguing that they also should learn that academic heat transfer is of very limited use in practice when you want to solve heat transfer problems in geometrically complex electronic systems.

6) Who would you recommend be the next person from the electronics cooling community to answer these questions?

Bob Moffat.


Clemens, many thanks!

27th July 2010 Nottingham

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This article first appeared on the Siemens Digital Industries Software blog at