Issue link: https://iconnect007.uberflip.com/i/948150
52 SMT007 MAGAZINE I MARCH 2018 the prints demonstrate less than 10% standard deviation. The print-by-print results in Figure 18 contains SM pad data. Only one in 40 boards satisfies the 0.48nl paste volume and 10% standard deviation criteria. The benefit of the stencil nano-coating is particularly obvious for this data set as an extreme number of low volume outliers occur on boards printed with the un-coated stencil. Conclusion The results of this printing research largely support the printing capability benefits offered by using nano-coated stencils. The larg- est benefit observed from the nano-coating was reduced print volume distribution scat- ter, particularly on the circuit boards with small undersized Cu pads. The discovery of one unique test condition combination that produced poorer printing performance with the nano-coated stencil is currently unexplain - able and warrants further review to confirm consistency of this behavior. This work has also identified the effect of pad structure to have profound influence on printing results, with the planar bare Cu board surface performing stand-alone best. However, demonstrated printing capability on bare board surfaces does not guarantee the same success on real patterned PCBs. Board design and manufacturing quality can significantly influence the print- ing outcome. While average print volume transfer efficiency results were similar comparing large pads against small pads, the print volume uniformity was noted better on large pads. M0201 printing capability on proper circuit board pads proved to be best controlled using the 80mm thick nano-coated stencil despite the unfavorable area ratio compared to the 50mm thick step stencil results. The 50mm thick step stencil aper- tures printed much larger than expected paste volume and produced a wider scatter in the print volume distribution attributed to poor squeegee wipe efficiency inside the step area. Further Work Work will continue to improve print quality results on both 80mm thick and 50mm thick stencil foils on this test board. A subsequent M0201 full assembly and reflow experiment is currently in plan. SMT007 References 1. M. Whitmore, J. Schake, C. Ashmore, "Factors Affecting Stencil Aperture Design for Next Generation Ultra Fine Pitch Printing," Proceedings of SMTA International Conference on Soldering and Reliability, May 2013. 2. Murata Manufacturing Co., Ltd., "GRM01121C1E100JE01 (008004, CH, 10pF, DC25V)," Reference Sheet, p.1. 3. www.marketwatch.com. 4. Murata Manufacturing Co., Ltd., "GRM01121C1E100JE01 (008004, CH, 10pF, DC25V)," Reference Sheet, p.25. 5. Product Assurance Committee Task Group 7-31b, "Acceptability of Electronic Assem- blies," IPC-A-610E, April 2010. 6. J. Schake, M. Whitmore, "Stencil Printing Solder Paste and Transfer Efficiency—Estab- lishing the Baseline," Proceedings of SMTA International, September 2004. Figure 18: Individual print boxplots – small Cu pads.