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48 SMT Magazine • March 2017 by Stephen Las Marias I-CONNECT007 Adrian Nishimoto, operation manager at Spectrum Assembly Inc. (SAI), talks about the critical factors to consider during flex circuit as- sembly, such as fixturing and accurate thermal profiling. He also mentions why jet printers are suitable for use in assembling flex circuits. Stephen Las Marias: What do you think are the major challenges in flex circuit assembly? Adrian Nishimoto: Helping our customers real- ize that fixturing is an integral part of success- fully building flex cir- cuits. We need good 3D Solidworks files, CAD or Gerber data to design car- riers able to provide a rig- id surface as the flex cir- cuits go through stencil printing, pick-and-place and reflow. In some cas- es, we also use specialized carriers for aqueous wash system. Las Marias: Please talk about specific steps in the flexible circuit assembly process that have the big- gest effect on yields. Nishimoto: Having tooling holes that keep the flex substrate rigid in a fixture during stencil printing and pick-and-place ensures better sol- der paste accuracy and component placement accuracy. The goal is to keep it flat and keep it from moving during these processes. The carrier is also critical if you have any type of conveyor system handling PCBAs in production. Las Marias: How do you address these challeng- es? Does the process require different parameters? Nishimoto: In addition to the fixturing consid- erations we've mentioned, accurate thermal profiling is also necessary. The carrier's thermal mass impact—the ability to absorb and store heat—needs to be taken into consideration. We do have our suppliers drill material out of the carrier to make them more web-like and less of a heatsink. That said, there isn't a one-size-fits-all solution to profiling because flex circuits come in all size ranges and that changes the optimum profile. FIXTURING: Key to Accurate Flex Circuit Assembly FEATURE INTERVIEW Adrian Nishimoto

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