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August 2016 • The PCB Design Magazine 61 shorter for points along the edge of the trace than it is for the center of the trace. Therefore, the edge cools more effectively, and the edge is therefore cooler than the center. Trace heating and cooling dynamics are much more complicated and subtle that per- haps we had previously understood. Acknowledgement This (and several other investigations I've made) would not have been possible without the generous cooperation of Prototron Cir- cuits, who provided a number of test boards for evaluation. I am also indebted to Scott Dau, a Seattle firefighter and part-time fire investi- gation instructor, who loaned me a thermal imager for capturing a variety of thermal im- ages, many of which are provided in Chapter 12 of my latest book. Norocel Codreanu of the University of Bucharest's Center for Techno- logical Electronics and Interconnection Tech- niques also provided assistance in looking at this relationship. And I want to especially thank Johannes Adam, of Leimen, Germany, for his collaborative support over the last 18 months. PCBDESIGN References 1. Douglas G. Brooks, PhD, and Dr. Johannes Adam, "PCB Trace and Via Currents and Tem- peratures: The Complete Analysis," available here. 2. "New Methods of Testing PCB Traces Ca- pacity and Fusing," Norocel Codreanu, Radu Bunea, Paul Svasta, Politehnica University of Bucharest, Center for Technological Electronics and Interconnection Techniques, UPB-CETTI, internal research project and report of UPB- CETTI/Winter-2010. For more information, click here. 3. Provided by Prototron Circuits for other investigations reported in reference 1. 4. The thermal images of all the traces I had available are included in reference 1, Chapter 12 and Appendix A9. 5. See reference 1, Chapter 4. For the last 20 years, Douglas Brooks has owned a small engineer- ing service firm and written numer- ous technical articles on printed circuit board design and signal in- tegrity issues, and he has published two books on these topics. He has given seminars several times a year all over the US, as well as Rus- sia, China, Taiwan, Japan, and Canada. His pri- mary focus is on making complex technical issues easily understood by those without advanced degrees. His latest book, "PCB Trace and Via Cur- rents and Temperatures: The Complete Analysis," was released earlier in 2016. YOUR TRACES HAVE HOT SPOTS! Figure 4: The cooling path for a trace is longer from the center of the trace than it is from the edge of the trace.

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