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70 SMT007 MAGAZINE I JUNE 2018 Board 2 that is commercially available from a leading dummy component and test kit supplier. The TV shown in Figure 1 provided an exceptionally thorough and detailed analy- sis in our earlier study and was used again in this study to provide continuity in data collec- tion and analysis. Features included: • Print-to-fail (PTF) patterns with combined pad sizes ranging from 3 to 15mils with shapes including circular, square and rectangular pads, defined with both copper (NSMD) and solder mask (SMD) • 0.4 and 0.5 mm BGA patterns. • Markings on the PCB are etched in copper rather than silkscreened with ink to eliminate the standoff effect of PCB nomenclature The smallest feature size printed in this study was 6 mil (150 µm) which produces an area ratio of 0.38 using a 4 mil (100 µm) stencil. The smallest feature size reported is 8 mil (200 µm), as the variation increases dramatically below this threshold, due in part to the low ARs and in part to measurement error. The TV used in this arm of testing was from the same production lot that was used in the previous study. The data was collected using a new panel for each print. No PCBs were cleaned and reprinted. The pad and aperture sizes, area ratios and theoretical volumes are shown in Table 1. Stencils The stencils employed current state-of-the- art technology which would typically be used for the fine feature applications that demand finer powder solder pastes. They were cut from pre-mounted name-brand stainless steel on a modern, diode laser by a high-qual- ity, US-based stencil supplier. One stencil foil was pre-mounted at high tension; the other at standard. The stencil supplier then applied a proprietary polymer nanocoating to the stan- dard tension stencil. The SPI results from each stencil were compared to those in the existing database from the previ- ous study. All apertures were sized one to one (1:1) with the test pads, with no reductions on any apertures. Laboratory Equipment & Print Parameters The test equipment included a DEK Hori- zon screen printer, Parmi Sigma X SPI machine and ASH video microscope in the AIM Applications Laboratory located in Juarez, Mexico. The test Table 1: Pad sizes, area ratios and theoretical aperture volumes for 4mil (100μm) foil. Figure 1: Jabil solder paste evaluation board.