This Month in Design007 Magazine: Thermal Fundamentals With Mike Jouppi

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The I-Connect007 team recently interviewed Mike Jouppi, one of the champions of thermal management in PCBs. Mike spent decades working on updating the old IPC current-carrying data, which dated back to the 1950s, and he is the primary architect behind IPC-2152— the standard for determining current-carrying capacity in printed board design. As Mike explained in this wide-ranging interview, even if you’re using the latest thermal design software, you still need to have a firm understanding of the fundamentals.

Andy Shaughnessy: Why don’t you start off by giving us a little bit of your background in thermal management?

Mike Jouppi: I had an internship when I was a junior in college at Hughes Aircraft Company. They gave me a stack of books and told me to start reading and asking questions, and that’s where I started. I was in a thermal analysis group at Hughes, and they used thermal analysis of electronics as a starting point for the new, young engineers who were working in the thermal area.

The nice thing about electronics is that you use all the fundamentals of heat transfer. They brought me up thinking about control volumes, which is a fundamental part of thermodynamics, and looking at all the energy coming into a system, all the energy going out, and how that energy gets stuck.

At the time, Hughes Aircraft was a nonprofit corporation, and we had really nice labs with a machine shop just for engineers. We were using a program called CINDA, the Chrysler-improved numerical differencing analyzer, which was a finite difference thermal analysis tool. Typically, our teams would be a mechanical designer, an electrical engineer, a circuit board layout person, and then myself as the thermal analyst. What I would do early is to get the best estimate of the power dissipation for all the components from the electrical engineer and do an early layout showing the power and resulting temperature distribution.

We would look at our worst-case environments, which was often flight or a lab environment that the electronics had to operate in, and we would work with the engineers early in the design to learn where our hot spots were, and then design around that. Getting the fundamentals down really well is what carried me through, and I use those even now to then. Fundamentals don’t go away.

Shaughnessy: What do you see when you look at the industry now? It seems like there’s a lot more focus on thermal. Do you see that happening?

Jouppi: The focus on thermal has always been there for the industries in which I worked. The mechanical engineering thermal side worked for a long time on getting a component database that was universal. There were thermal models, a number of different modeling structures for components that people tried to get as a standard structure to work from, and a lot of work was done there, but I didn’t see everyone buying into it to where it became a commonly used method for all companies. It would have been nice to have that standardized in such a way that it would address both earth and space environments.

To read this entire conversation, which appeared in the September 2020 issue of Design007 Magazine, click here.


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