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12 DESIGN007 MAGAZINE I SEPTEMBER 2020 Feature Interview by the I-Connect007 Editorial Team The I-Connect007 team recently interviewed Mike Jouppi, one of the champions of ther- mal management in PCBs. Mike spent decades working on updating the old IPC current-carry- ing 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 ex- plained 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 ther- mal management? Mike Jouppi: I had an internship when I was a ju- nior 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 elec- tronics as a starting point for the new, young en- gineers 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 thermodynam- ics, 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 Chrys- ler-improved numerical differencing analyz- er, which was a finite difference thermal anal- ysis 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 engi- neer and do an early layout showing the power and resulting temperature distribution. We would look at our worst-case environ- ments, which was often flight or a lab envi- ronment that the electronics had to operate in, and we would work with the engineers ear- ly in the design to learn where our hotspots were, and then design around that. Getting the fundamentals down really well is what carried Thermal Fundamentals With Mike Jouppi

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