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December 2017 • SMT Magazine 31 Apertures were also cut into the center of each step area for comparison. The aperture layout is shown below (Figure 6). Each stencil was made with two sets of steps and apertures. One set of steps and apertures were coated with a fluoro-polymer nano (FPN) coating (Figure 7). Figure 6: Step stencil aperture design. Figure 7: Step stencil contact side with FPN nano-coating. Figure 5: Step down pocket design. The effects of the FPN coating were com- pared to the uncoated part of the stencil on printing of solder paste. A 10-print study was run on each step stencil using a popular no clean, SAC305 Type 4 solder paste. The cir- cuit boards used were bare copper clad materi- al 0.062" (1.57 mm) thick. The printer used was a DEK Horizon 02i. The printer parameters are shown below (Table 1). STEP STENCIL TECHNOLOGIES AND THEIR EFFECT ON THE SMT PRINTING PROCESS