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70 SMT Magazine • May 2016 by Dave Becker ALL FLEX FLEXIBLE CIRCUITS LLC The market for rigid PCBs is estimated to be about 10x the market size for flexible printed circuits (FPCs). As a result, the equipment infra- structure is driven primarily by the needs of the rigid board market. This is true of both equip- ment used to fabricate the circuitry (image, etch, copper plate, AOI, etc.) and equipment used for component assembly (wave solder and SMT assembly). Flexible circuits are often sold in multiple- up panels or arrays to facilitate the assembly of SMT components. Coordination between the desires of the assembly supplier and the fabrica- tor can have a significant effect on costs based on material/panel utilization. Fabrication pan- els are generally larger (12"x24" and 18"x24" are common sizes in the U.S.) than assembly panels. Assembly panel sizes should be efficient subsets of fabrication panel sizes to optimize material utilization. The math for determining parts per panel becomes a bit more complicated since fabrication panels will have a "keep out" border around the perimeter of the panel for tooling holes, fiducials, and test coupons. In addition to considerations for material utilization based on circuit fabrication panel sizes, the quantity of circuits on a given pan- el size will be a function of several other vari- ables. These variables include: size of the cir- cuit, components to be populated, registration requirements, and assembly equipment capa- bility. Multiple fiducials per panel may slow SMT placement rate, but this tradeoff is often trumped by the yield improvement and/or re- work avoided. Positioning parts accurately for SMT place- ment is a key to successful assembly. Custom carrier pallets are sometimes designed to hold singulated circuits. Another option is to use a Flexible Circuit Component Assembly… and a Math Lesson aRticlE

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