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50 SMT Magazine • March 2017 Las Marias: How does flex circuit assembly differ from standard PCB assembly? Nishimoto: Because the material is flexible, all secondary operations need to use extra care in processing. If there are ceramic capacitors or other large ICs, it becomes important to make sure that the substrate is not flexed in handling because that will damage the solder joint. Las Marias: What about the challenges with re- spect to flexible circuit materials? Nishimoto: We don't see any challenges as long as we can create a fixture to keep it rigid. Las Marias: Do customers call out a specific brand name of material to use when dealing with flexible printed circuits? Nishimoto: There is no specific brand name of material called out. In some cases, the substrate is exotic, but most are polyimide materials. Some customers specify the supplier on the ap- proved vendor list, but in many cases, they de- pend on us to identify suppliers and give them choices to qualify that meet their requirements in terms of material performance and lead-time. Las Marias: Which practice has the greatest im- pact on the quality of flexible circuit assemblies? Nishimoto: Following industry-standard best practices in initial design and layout. Since flex circuits are folded up and put in tight enclo- sures, it is important to reduce points of fail- ure, such as the location of points of intercon- nect. For example, a really long connector may require a rigid flex design, which uses stiffener rather than a 100% flex design. Las Marias: In which end markets are you seeing increasing use of flexible circuits? Nishimoto: Primarily, we are seeing them in medical and consumer applications. Las Marias: What are the key things for OEMs to consider when choosing an assembly partner for flexible circuit assemblies/projects? Nishimoto: First is prior experience with flex cir- cuit assembly. Then, they should have a good relationship with one or more board carrier fab- ricators. Lastly, they should have an expertise in thermal profiling in reflow and strong disci- pline in work-in-process handling practices. Las Marias: Are there new technologies out there that will significantly impact or benefit the flexible circuit assembly process? Nishimoto: When you have rigid-flex combina- tions or stiffeners in use, you have two different heights—which makes it impossible to screen print without specialized fixturing. Paste jet printers like the MY500 we use are more adjust- able and do not have that constraint because it allows us to tailor the amount of solder on indi- vidual components without the use of a stencil. Las Marias: Thank you, Adrian. Nishimoto: Thank you. SMT FIXTURING: KEY TO ACCURATE FLEX CIRCUIT ASSEMBLY Bob Wettermann, president of BEST Inc., talks with I-Connect007 Editor Stephen Las Marias about the chal- lenges in rework, and how his company is helping their customers address these problems. He also discusses his paper presentation at the technical proceedings at IPC APEX EXPO 2017. Watch The Interview Here Real Time with...IPC: BEST Talks Rework Challenges and Opportunities

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