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FLEXO Magazine : September 2011
alignment, registration and precise impression. Also, thin plate technology would be a wise consideration for producing printed electronics. Plates of thicknesses as low as 0.030 inches would help achieve precision within small features. The study at hand yielded several specific conclusions regarding the reproducibility of specific characteristics using flexographic printing to produce printed electronics. Ink film thickness and surface uniformity. According to the profilometer analysis of the printed test targets, flexogra- phy produces a relatively uniform layer of ink, except near the edges. Essentially, flexography was able to produce surface uniformity within 0.5 microns. Additionally, al- though perfect uniformity was not achieved, there were no areas of print that had no ink. This is important for printed electronics because missing ink would cause an electri- cal component to lose its functionality. According to these results, the standard for ink film thickness and surface uniformity necessary for many printed electronics could probably be met through flexographic printing. Registration. Unfortunately, some of the 10-micron lines for the registration targets did not hold on the plate and therefore did not hold on press either. Most impor- tantly, the registration marks were not reproduced in any recognizable fashion. The grids of 10-micron lines printed to the equivalence of smudges of ink. The registration target, while attempting to measure registration, mea- sured only feature size and supported the evidence that flexography cannot feasibly reproduce 10-micron lines or 10-micron gaps, especially not the two together. The inability to produce such small grids of lines may have to do with the plate itself, rather than the printing. Although the plate photos displayed some clarity of lines within the registration grid, there are no defined valleys between peaks of lines. Edge definition. Edge definition proved to be better with cross-direction lines. For the analysis of edge definition, the designed target was not as useful as the minimum feature size target. Because printed electronics would not only require precise edge definition but also very small feature sizes, it was more applicable to measure the edge definition of 50-micron lines rather than 0.125-inch lines, as in the edge definition target. Minimum feature size. Unfortunately, it is not feasible to produce feature sizes of 10 microns through current flexographic printing technology. An ideal printing method for printed electronics should be able to reproduce 5-mi- cron lines. Flexography on the other hand, cannot create a plate with 5-micron lines, cannot print 10-micron lines and cannot produce consistent, solid 20-micron lines. It is reasonable to conclude that a 25-micron line is the mini- mum feature size that flexography is capable of achieving consistently. Notably, the lines printed in the cross-direction are much more uniform than those printed in the print direction. Although the test target was created to produce lines of 10 to 50 microns, the printed lines were not of the desired widths. The 20-micron line, which was the smallest reproduc- ible line, was in fact measured to be approximately 25 microns, while the 50-micron line was measured to be approximately 75 microns. Moreover, the feature size target tested minimum achievable gaps. Flexography cannot realistically reproduce gaps of 10 microns, let alone 50 microns. None of the gaps on the test tar- get, from 10 to 50 microns were reproduced with any clarity. To the naked eye, there seems to be a fine line of gap definition for Figure 2: Each peak in the above chart shows various thickness of the ink film. The first line appears to have a very sharp edge, but the ink film thickness varies drastically between lines. There is roughly a 1.5-micron difference between highest level of ink and the substrate surface. Figure 3: The chart seems to show that the ink film thickness varies drastically, with differences from 0.4051 microns to -0.2224 microns. Substrate smoothness and inconsistencies in the adhesive could have affected these results. www.flexography.org SEpTEmbEr 2011 FLEXO 73 www.flexography.org SEpTEmbEr 2011 FLEXO 73