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February 2016 • SMT Magazine 73 locations. After initial calibration, an ASC AV862 offline semi-automated measuring system was utilized to take the measurements. This system used Gerber data as input information in order to find the location of each of the solder pads. After this set up the camera scans each of the lo- cations that it recognizes as having solder paste and measures the height and volume amongst seven parameters per pad location. These results were then tabulated, graphed and analyzed. results Figures 3 and 4 are the box and whisker plots for the solder paste where for the plastic adhe- sive-backed film and miniature metal stencils. Other charts and data including solder height, release efficiency and a comparison between theoretical versus actual print volumes was part of the complete study. Sneak Peak at the Conclusion The print height using the plastic film adhe- sive-backed stencil is more consistent and repeat- able compared with the more traditional minia- ture metal rework stencil. This can be linked to the process of printing using the adhesive back- ing of the plastic film stencil as it keeps the sol- der paste from squirting out from underneath the stencil while also preventing it from shifting around during the manual printing cycle. Due to the adhesive holding the stencil to the board, the plastic film stencil also allows for multiple print passes to ensure the apertures are filled up. Sub- sequent prints of the mini metal stencil allows for the build-up of solder paste on the aperture walls and hence smaller volumes of paste being deposited on the board. The print volume aver- ages were nearly identical for both of the popu- lations, but the consistency of the solder paste Figure 4: box and whisker plot for mini metal rework stencil for solder paste height trials. reWork site PriNtiNg usiNg miNi steNcils—Plastic adHesiVe Vs. metal

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