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82 SMT007 MAGAZINE I JUNE 2018 high tension. Use of nanocoating also appears to outweigh the effective benefit of using T5 to T4 solder paste, which in turn, appears to have a greater effect than the tension. There- fore, the effects of the studied variables on overall print quality can be ranked from high- est to lowest as: nanocoating, powder mesh size, and tension. It should be noted that, although high tension foil mounting did not show a consider- able impact on this test, the test vehicle itself does not have a high aperture density, and the foil is a 4 mil-thick, hard stainless steel. Sten- cils with higher aperture densities, or thinner or more ductile foils may realize measurable benefit from higher mounting tensions. It should also be noted that the combina- tion of high tension and nanocoating was not tested. Based on the results of this study, the combination may be tested for statistical anal- ysis, but it is anticipated that the effect of nanocoating will far outweigh the effect of foil mounting tension on this test vehicle. Conclusions The solder paste printing process represents the greatest opportunity to introduce defects into the SMT assembly process. Therefore, any technology that can reduce the risk is always worth investigating. This study demonstrated that the most significant advantages in both transfer effi- ciency and volume consistency were realized by using nanocoated stencils, particularly as aperture ratios shrink below 0.62. It should be noted that AIM has no commercial interest in stencil or coating technologies; AIM's purpose in investigating the effect of the coatings is simply to provide users with the best possi- ble process recommendations. In most cases, moving from T4 to T5 provided print qual- ity improvements in both transfer and consis- tency, but the gain was minimal compared to that of the nanocoating. Nanocoating provided a wider process window than T5 solder paste. Additionally, finer mesh solder powder, such as T5, have Figure 17: Comparison of effect of foil mounting tension on print quality with Type 4 solder paste and worst-case scenario pad design after 90-minute pause.