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Research paper : Development of laser-assisted inkjet printing technology (A. Endo et al.)−14−Synthesiology - English edition Vol.4 No.1 (2011) become possible to widen the distance between the substrate and nozzle, and this will enable formation on materials with large step structures.The technological issues of the conventional industrial inkjet technology were organized and the essential issues were extracted, to set the direction, technological issues, and objectives to be achieved for the laser-assisted inkjet technology.4 Effect of the laser-assisted inkjet technology4.1 Achievement of high aspect ratio of wire by laser assistanceFigure 7 shows the results of the formation on non-surface treated glass plate to study the effect of laser assistance on the wire width, to form fine wire with high aspect ratio.When the formation was conducted under conditions of droplet diameter size of 25 m, ejecting frequency of 3 kHz, and stage speed of 60 cm/min, the wires formed by the laser-assisted inkjet technology have a width of 10m and a thickness of 11 m. Compared to the wire forming without laser assistance, the wire width decreased from 230 m to10 m, or 1/20 time less, and the wire thickness increased from 0.8 m to 10 m, or about 12.5 times more. An extremely large improvement was observed.Figure 8 shows the 3D configuration obtained by laser microscope. The wire formed by laser assistance was very different from the wire formed by conventional inkjet printing. The uneven wire formations such as the coffee stain phenomenon where the grooves are formed on both sides of the wire[9][11] and the bulge phenomenon where the wire width bulges out in some places[12] were not seen, and the wire had an even, smooth surface with a “semi-cylinder structure”.It was possible by this approach to form a wire with high aspect ratio of 1 that is much higher than in che case of using the conventional inkjet method. Moreover, a wire with width smaller than the droplet diameter could be formed on untreated substrate surface using our approach.In the conventional technology, even if the substrate surface treatment was done, wire thickness of about 290 nm[6] was the limit for one coating for a wire with width of 10 m formed on the substrate with contact angle of 90°. Therefore, assuming the resistivity of the conductor at 2.0 ·cm, the resistance per 1 cm of formed wire would be about 70 /cm for wire formed with conventional technology with surface treatment. But the actual resistance value was about 6 /cm for a wire obtained onto an untreated surface using laser assistance. The improvement observed in the wire resistance is over 10 times that of the conventional approach when laser assistance is used.To get the same wire resistance by concentional inkjet methods, 13 or more recoatings are necessary. The potential for dramatic improvement of throughput by using laser assistance can be easely deduced from this comparison.Moreover, since high precision in positioning and landing were required for recoating, laser-assisted method may solve these issues also.4.2 Electric property of the wireTo develop the laser-assisted inkjet technology as the surface mounting technology specifically for the wires on the IC chip, we investigated the properties for the high frequency transmission line of the formed wire. The high frequency transmission property of the wire is affected greatly by the cross-sectional form and the precision of pattern. Therefore, the pattern of the coplanar transmission line, where the central conductor and ground conductor are arranged on the Fig. 7 Effect of laser assistance on wire width(a) Without laser assistance (b) With laser assistanceFig. 8 3D configuration and cross-section of the wire formed by laser-assisted inkjet technology(a)(b)100 µm100 µmWidth : 230 µmThickness : 0.8 µmWidth : 230 µmThickness : 0.8 µmWidth : 5~10 µmThickness : 10 µmWidth : 5~10 µmThickness : 10 µm30025020015010050002468101210 µm0.8 µm30025020015010050002468101210 µm230 µmWire thickness (µm)Wire thickness (µm)Wire width (µm)Wire width (µm)10 µm11 µm0051015202530354045502468101270.740.080.016.2µm40.00.0 µm0.0 µm10 µm11 µm0051015202530354045502468101270.740.080.016.2µm40.00.0 µm0.0 µmWire thickness (µm)Wire width (µm)

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