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50 DESIGN007 MAGAZINE I NOVEMBER 2024 A Word to the Wise Rules of thumb are arguably handy to use in the early design process, but they need to be used with some caution: • Some rules may oversimplify complex interactions. In PCB design, this can include thorny challenges such as heat dissipation or impedance control design calculations. • Remember the era in which a rule of thumb was developed. ose created for older manufacturing technologies, pro- cesses, and practices may be irrelevant in more modern processes or materials. • Avoid assuming that rules of thumb are unaffected by variations in materials and processes used. ey need to be carefully matched to the current design. Summary Rules of thumb can help guide and speed designers and engineers through initial deci- sions in the design process. However, tradi- tional engineering practices and formulae remain highly important, even indispensable, as they provide the precision needed for final designs. Rules of thumb can simplify the myr- iad complex relationships that exist in circuit design and manufacturing, but tested and proven formulae derived from years of manu- facturing practice that tacitly validate rules should be supported with empirical data when precision is critical and failure is not an option. Using rules of thumb in PCB and flex circuit manufacturing can also enhance efficiency and decision-making, but they should be employed judiciously. Balancing these guidelines with detailed calculations and a clear understand- ing of the specific requirements of a project will lead to better designs and more successful outcomes. Always challenge assumptions and seek to validate decisions with data to sepa- rate myths from reality and ensure the ultimate reliability of the product. Above all, enjoy the process. DESIGN007 References Flexible Circuit Technology, 4th Edition by Joe Fjelstad. Joe Fjelstad is founder and CEO of Verdant Electronics and an international authority and innovator in the field of electronic interconnection and packaging technologies with more than 185 patents issued or pending. To read past columns or contact Fjelstad, click here. Download your free copy of Fjelstad's book Flexible Circuit Technology, 4th Edition, and watch his in-depth workshop series "Flexible Circuit Technology."