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SMT-Jun2018

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24 SMT007 MAGAZINE I JUNE 2018 good example of something that is simple in relative terms compared to the flexible circuit layers; however, it drastically complicates the assembly process by limiting handling and cleaning options post soldering. However, if you process the soldering and cleaning of the assembly first, it is labor intensive and costly to apply the pressure-sensitive adhesive in piece form. It's a double-edged sword. Las Marias: Which parts of the assembly process are greatly impacted when doing flex circuit assemblies? Michaud: When considering assembly, panel- ization and fixturing during design become important, as to panel size and panel stabil- ity. The number and type of components will dictate these parameters. These are important to facilitate the proper oven location during reflow. Oversized panels or unstable panels can greatly affect reflow and profile results in turn affecting yield and cost. Singulation post assembly is always a concern that is flexible circuit- and component-specific. Las Marias: What strategies do you employ to address these challenges? Michaud: Understanding the capabilities of the assembly equipment and its limitations is vital. Having calibrated equipment and a known repeatable process is key. Outlining post assembly can be accomplished through steel rule die, hard punch dies or lasering. Depending on the components that are assem- bled, the number you are outlining, and the required outline tolerance determine the best and most cost-effective route. Las Marias: How different is the assembly of flex circuits from rigid- or rigid-flex circuits? What are the critical factors to consider? Michaud: Flex circuits are typically more sensi- tive to assembly processes than their rigid-flex counterparts. In either case, as both products are hydroscopic, pre-bake cycles are a critical precursor to any assembly. In flex assembly, consideration must be given to added support for solder pad and/or through-hole areas with stiffening materials, preventing stress from transitioning to the soldered joint as, of course, flex circuits want to flex. In rigid-flex, you are more typically assembling to the rigid area and it provides self-stress relief. Proper pad sizing and thermal relief during design helps opti- mize reflow and hand solder assembly. Las Marias: What new technology or process do you employ to ensure flex circuit assembly success? Michaud: We use a variety of SaaS (software-as- a-service) collaboration systems that allow us to engage with customers, vendors, and inter- nally to ensure the proper design, compatibility of materials, and the non-conflict of manufacturing processes used, in real time. What we are trying to facili- tate here is the involvement of evolved technology in communi- cation. We've been using collab- orative technologies from the U.S. to problem solve issues at Miraco South within hours—not days, not weeks, without personnel board- ing flights. A photo or a video appears, and a meeting is held

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