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78 The PCB Magazine • August 2015 Universal Criteria: Whether your PCBs are being manufactured domestically or off- shore, certain things are universal. Quality spec- ifications such as IPC class, FAIR requirements, and testing requirements do not change. Some of these specifications may not be as critical at the prototype stage and could be waived, but the interpretation of the specification will be consistent. Designing to maximize yields may not be as critical with a prototype order, but with the higher volumes typically as- sociated with offshore produc- tion, expected yields should be considered. There are universal criteria for maximized yields. Increasing holes sizes, pad siz- es, line width and space will all improve yields at the manufac- turer and have a direct impact on cost. Acceptance of X-outs should also be considered, as al- lowing them in your delivered array will have a direct impact on cost. If X-outs are not al- lowed, both domestic and off- shore manufacturers will factor in the yield loss associated with scrapping any good pieces in an array that has an X-out. If X-outs are not allowed, this should be clearly communicated to avoid any misunderstanding. Significant Variation: Preferred mate- rials can vary significantly between domestic and offshore manufacturing. This preference is typically a function of material availability and cost. Logically, offshore suppliers will prefer to use materials that are produced locally. These materials are more readily available, with lower transportation costs. Most offshore suppliers will also use the materials that are more com- mon in the U.S., but pricing will be higher and lead time longer. Be careful not to over specify materials. Ref- erencing the appropriate IPC slash sheet, rather than the specific material, allows more flexibil- ity for the supplier. This flexibility will result in lower cost and shorter lead time. If more con- trol is required for material selection, using an approved list of materials that has been tested and approved is another option that allows the manufacturer flexibility to use their more pre- ferred materials, while giving the designer more control of materials being used. Another aspect that varies significantly is panel utilization. Domestically, the most common panel size is 18" x 24" with 16" x 22" of usable space for the manufacturer, and it is most cost-effective to design the part or the array to best fit that space. Offshore manufacturers have much more flexibility with their panel sizes, use many different panel sizes to best utilize material, and generally work with larger pan - els. Offshore, it is more criti- cal to design the array to best utilize the material within the array so that overall, array size has much less of a cost impact. Recap When looking for the smoothest transition from do- mestic prototype to offshore production manufacturing, re- search suppliers and select one that can demonstrate knowl- edge of the offshore facility's technical capabilities, material preferences, and that clearly has a streamlined form of communica- tion. Quality and testing specs are universal and should transfer from one facility to the other with no issue, but special attention should be given to controlled impedance, materials and panel uti- lization, as these can vary significantly between domestic and offshore manufacturing facilities. A smooth transition from domestic prototypes to offshore production does not need to be dif- ficult, but it does need to be well planned. PCB DESIGNING FLEx CIRCUITS FoR DoMESTIC PRoToTYPING continues Flex tAlk Tara Dunn is the president of omni PcB. She works with PcB designers and purchasing organi- zations to find the best fit solution based on volume, technology and lead-time requirements. click here to reach Tara. Be careful not to over specify materials. referencing the appropriate ipC slash sheet, rather than the specific material, allows more flexibility for the supplier. this flexibility will result in lower cost and shorter lead time. " "

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