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72 DESIGN007 MAGAZINE I DECEMBER 2020 What do you do when you are designing a flexible circuit and need to go "way outside the box" to get the desired end-result? Let's look at a few success stories. Gold Conductors Flexible circuits are commonly fabricated on polyimide dielectrics with copper conductors. Fabricators purchase the raw material as lami- nate with rolled annealed copper bonded to the base dielectric. Interestingly, I have been see- ing an increase in demand for gold conductors on flex materials rather than copper conduc- tors. This combination of materials provides a much more biocompatible solution for medi- cal applications. Exciting, right? But this sig- nificantly changes the manufacturing process and moves this design into something "out of the ordinary," which needs to be accounted for and understood in the early design phases. To meet this requirement, the fabricator piv- oted from subtractive etch processing to addi- tive PCB fabrication technology. With subtrac- tive etch, as the name implies, the unneeded copper is being etched away from the panel, creating the circuit pattern. While this addi- tive technology is more commonly used for copper conductors with very fine feature sizes Communicating Outside the Box Is Key to Flex DFM Flex Talk by Tara Dunn, AVERATEK