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20 SMT Magazine • February 2014 experiment #2: New Stencil Materials 1) Print Yields The FG SS with both the first- and second- generation nanocoatings produced 80% yield. The experimental SS without nanocoating produced 90% print yield, and with the new- generation nanocoating produced a 100% print yield. The experimental electroform (EF) stencil with the new nanocoating also produced 100% print yield, but the experimental EF stencils with first-generation or no nanocoating only produced 60 and 70% yields, respectively. Print yields for the different materials and coating are compared in Figure 9. 2) Transfer Efficiency All stencils tested transferred at least 80% on the microBGAs and close to 100% on the 0201s. Figure 10 shows the microBGA results. The experimental SS and EF stencils without any nanocoating at all transferred 91 and 92% re- spectively, approximately 10% higher than the production process. The same materials with second-generation nanocoating released more than 86%, a less substantial yet noteworthy 5% increase from the benchmark. The other sten- cils performed in the expected 81–83% range. The TE of the 0201s hovered around 100%, with the untreated experimental materials showing the highest release, and the treated ma- terials showing the second highest. The trend shown in Figure 11 is identical to that of the microBGAs. Another repetitive trend observed in all print tests is the slightly higher TE (3–6%) for components oriented at 0° versus those ori- ented at 90%. 3) Variation The lowest CV for the microBGAs was on the experimental EF stencil coated with sec- ond-generation nanocoating, at 10.8%. The next lowest was the experimental SS with the second-generation nanocoating (Figure12) at 11.4%. This trend is again observed in the 0201 CV data, but transposed, with the Nano2 exper- imental SS at 10.9% and the Nano2 experimen- tal EF at 11.3% (Figure 13). The remainder of the stencils all produced higher variation. FEATUrE Figure 9: Effects of stencil alloy and coating on print yields. Figure 11: Effects of stencil alloy, coating and com- ponent orientation on 0201 transfer efficiency. Figure 10: Effects of stencil alloy and coating on bgA transfer efficiency. FINe-TuNING THe STeNCIL MaNuFaCTurING PrOCeSS continues