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44 SMT Magazine • October 2015 duction. Frequent changeovers create a bottle- neck in assembly speed. Stencil manufacturing and lead time, as well as occasional replace- ment, add to the delays. Each PCB design and design change requires a new stencil. Thus, stencil costs and two- to three-day time delays can happen with multiple rev changes. Stencil- free jet printing technology has been developed to meet the demand for greater flexibility in modern electronics production, significantly improving the throughput speed. The CAD data (or Gerber data) for a particular PCB, compiled off-line, is sent to the ink jet printer for instant printing. High-speed solder paste depositing by jet printing is made possible by a unique ejection method. The technique ejects tiny droplets of solder paste from a cartridge through an ejec- tor mechanism onto the PCB at the positions required by the Gerber file. The ejector system operates at speeds up to 500 droplets per sec- ond, which enables solder paste printing on the fly. The different types of solder paste used for jet printing are delivered in standard cartridges. The cartridge is swiftly snapped into the ma- chine in seconds, so you can switch from tin/ lead to lead-free solder paste in a matter of min- utes. A barcode label on the solder paste car- tridge and an identification chip in the cassette ensure that the wrong type of solder paste, or solder paste past its due date, is never loaded by mistake. The electronic identification bar- code label and cassette memory make machine settings automatic. Once the paste code type is entered, the printing can start. Touchless jet printing technology applies no force to the PCB, hence no support pins are needed, further improving start-to-finish speed. In addition, the print program automatically aligns and adjusts to the PCB board stretch based on the fiducial marks. Accurate temperature control ensures that proper viscosity of the sol- der paste can be maintained at all times, which in turn leads to higher levels of application ac- curacy. The process is completely controlled by software. The solder paste volumes can be altered "on-demand." The ink jet printing pro- cess allows control of solder paste deposits with precision, in 3D. It is possible to fine-tune the volume, area coverage, height and layers of sol- der paste that need to be applied for every indi- vidual pad, component and package. Ink jet can print pads for components with pitches as small as 0.4 mm (16 mil). With this level of control, you can print small deposits next to large ones (e.g., 0201s right next to connectors, something stencils have a hard time doing, resulting in time-consuming hand solder operations). For PCB assembly shops, the less on-line operator involvement needed, the faster it is to assemble a PCB while consistently maintaining higher levels of quality. To maintain a high degree of flexibility, printing programs can easily be ad- justed on the fly if revisions are needed. The absence of stencils ensures other time- reduction benefits, such as no need for special paper for underside wiping, no need for stencil cleaning machines, no need for clean up and storage of stencils, and no risk of damaging the stencils during handling (damaged stencils re- sult in time delays to reorder, as well as faulty solder joints that need time to touch up). The lead time for the arrival of a new stencil delays production for several days, which results in de- livery delays to the customer. SMt technoLoGIeS to enAbLe QuIcK-turn Pcb ASSeMbLIeS FeATure Khurrum dhanji is the ceo and managing partner at imagineering inc. " The process is completely controlled by software. The solder paste volumes can be altered "on-demand." The ink jet printing process allows control of solder paste deposits with precision, in 3d. "

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