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46 DESIGN007 MAGAZINE I NOVEMBER 2024 and detailed calculations, and can help engi- neers and designers speed up the decision- making process, especially in complex scenar- ios. ey are useful, but it's essential to know when to apply rules of thumb, which ones to prioritize, and when to rely on more precise calculations or formulas. Where Rules of Thumb Work Best Early phases of design: Rules of thumb are best applied in the early phases of the design and development process where they can help design and manufacturing engineers make quick assessments about board dimensions, component requirements and energy density limits, layer counts, and board materials. ey can help the product developer or develop- In the early days of electronics manufactur- ing—especially with PCBs—there were no rules. Engineers, scientists, and technicians largely felt their way around in the dark, mak- ing things up as they went along. ere was a great deal of innovation, guessing, and testing to make sure that early guidelines and esti- mates were correct by testing them. Still, they frequently made mistakes. at said, they employed solid mechanical and electrical engineering practices, much like they do today. Over time, engineers have developed the "rules of thumb" in printed circuit board and flex circuit manufacturing. ese are simplified guidelines based on the practical experiences of both individuals and the industry at large, rather than using strict Rules of Thumb: A Word to the Wise Flexible Thinking Feature Column by Joe Fjelstad, VERDANT ELECTRONICS