SMT007 Magazine

SMT-July2014

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70 SMT Magazine • July 2014 by Rachel Miller-Short THE SHoRT SCooP CoLUMn More Stencil Questions (and the Answers!) My March Short Scoop column, 10 Com- mon Stencil Questions, brought in a slew of new questions from customers. Do you know the answers? 1. What are my fiducial choices and how do they differ? Yes, stencils require fiducial markings to make sure the stencils are aligned correctly to properly print the pattern, as most people know. What they might not know is that there are ac- tually several types of fiducials, and when you select a stencil, you must choose one of them. The fiducial choices available today depend on the stencil manufacturer you use and/or your own requests, but truthfully, there really are only two predominate types. One is half- etched and filled, which have an etched pocket in the stencil at the fiducial location that is then filled with a black epoxy. Ultimately, these of- fer one of the strongest contrasts for the visual printer cameras, but they are an older technol- ogy and often, the epoxy falls out at the least opportune time. The other predominate type is a laser tat- tooed fiducial, which is a relatively newer tech- nology. These are applied by a laser (usually the same one that cuts the apertures for a laser sten- cil). In this technology, the laser truly burns the

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