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60 SMT Magazine • March 2017 Las Marias: What specific steps in a flexible circuit assembly process have the biggest effect on yields? Galloway: We find panelization is critical. The contract manufacturer and design team need to discuss the depanelization strategy and make sure the proper tools are specified. It is also important that the layout uses appro- priate clearances on edges that will be cut or routed. Las Marias: How should these challenges be addressed? Galloway: Typically, flex boards are not square. We need to hold them flat and provide them with adequate support. We typically fix- ture with FR4 and use double-sided kapton tape to hold it down for most situations. When the application warrants it, we go to a fixture house and have custom fixtures with tooling pins made. Las Marias: How different is the flex circuit as- sembly from the standard PCB assembly? FEATURE INTERVIEW by Stephen Las Marias I-CONNECT007 Screaming Circuits, a division of EMS firm Milwaukee Electronics, specializes in building short-run, one-off, and prototype PCB assem- bly, with rapid turn times and instant online quoting and ordering. Mike Galloway, technical team supervisor at Screaming Circuits, discusses with SMT Maga- zine the biggest challenges when it comes to as- sembling flex circuits, the critical factors affect- ing yields, and the key considerations for OEMs when selecting contract manufacturing partner for their flex circuit assemblies. Stephen Las Marias: Mike, what are the ma- jor challenges in flex circuit assembly? Mike Galloway: We have found that you need to control moisture sensitivity level (MSL). We are treating them as MSL 5. We are baking them on receipt and sealing them in moisture sensitive packaging. If top and bottom side as- sembly will have a time gap of several hours, we will reseal them during the production process.