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24 DESIGN007 MAGAZINE I NOVEMBER 2024 e idiom "rule of thumb" is oen used in electronics design and has its origins in the practice of measuring roughly with one's thumb. Rules of thumb are easy-to-remember, broadly accurate guides or principles based on practice rather than theory. ey are used to help feed our intuition to find a quick solu- tion based on experience. We are oen forced to use rules of thumb in PCB design in the absence of expensive analysis tools. We also use them to get quick ballpark figures initially and then fine-tune the numbers with further analysis. We can use rules of thumb as a sanity check to assess whether we are using our tools correctly. In this month's column, I will pres- High-speed Rules of Thumb ent some commonly used and helpful rules for high-speed PCB design. e most popular rule of thumb is prob- ably that "Rules are meant to be broken." is implies that there are times when we should think for ourselves and not obey every rule pre- sented to us blindly. I find that with every PCB design I complete, there is at least one rule that needs to be broken to accommodate a certain situation. All board designs are different. e following is a list of rules of thumb extracted from the various columns and seminars I have written over the years. If you require clarification on any rule, please read the appropriate Beyond Design column. At the Beyond Design Feature Column by Barry Olney, IN-CIRCUIT DESIGN PTY LTD / AUSTRALIA