Issue link: https://iconnect007.uberflip.com/i/1533085
MARCH 2025 I DESIGN007 MAGAZINE 71 a. is is an unreliable forming method. e circuit should be formed consis- tently using a fixture. e flex needs sufficient radius and cannot not be bent sharply. Bending guidelines in IPC-2223 should be followed to ensure reliability. i. e customer implemented a fix- ture to repeat the bend consistently. b. Traces should be run perpendicular to the bend. is will make the bend more reliable. c. Changing panel layout so that copper grain direction runs perpendicular to the bend helps as well. 2. is circuit originally was set up with a polyimide coverlay/LPI combination that overlapped right at the bend. Liquid photoimagable solder mask (LPISM) was needed for SMT accuracy in the stiffened area. e problem was that there was not enough room for this transition as the component was right up against the rigid- to-flex transition area. a. To fix this problem, we changed the outer cover to all polyimide coverlay to eliminate the transition of the LPISM/ polyimide combination at the bend. 3. A trace is only 0.0026" away from the trim border. a. is may cause the trace to be exposed on the edge aer blanking. i. To solve this issue, we were able to reduce the trace width by 0.001", move trace 0.0005" away from the border. e border has a ±0.002" tolerance. We then moved the outline out to the high end of the tolerance. is now allowed for a 0.0046" trace to border. With the laser trimming of the circuit, we had the accuracy to meet the print and not expose the trace. We cleaned up the data per these solutions, and sent the data back to the customer for approval, explaining the reasons for change, and received approval. Designing flexible circuits requires a collab- orative approach that balances creativity with practicality. Each decision, from stackup con- figuration to via placement, can significantly impact manufacturability, cost, and reliabil- ity. It is critical to work closely with an expe- rienced application engineer to ensure that designs adhere to the best practices outlined in IPC standards and achieve optimal manu- facturability. By leveraging expert guidance, designers can achieve robust, high-yield solu- tions that meet both functional requirements and budget constraints. DESIGN007 Tony Plemel is a senior applications engineer at Flexible Circuit Technologies.