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Research paper : Development of laser-assisted inkjet printing technology (A. Endo et al.)−15−Synthesiology - English edition Vol.4 No.1 (2011) same plane, was formed using only the laser-assisted inkjet technology and the high frequency transmission property was measured.When the transmission line and the package were considered by the parameter measurement of the transmission property (S21) and the reflection property (S11) in the high frequency region using the Thru-Reflect-Line (TRL) calibration method by the network analyzer, it was possible to accurately observe which frequency could be used.Figure 9 shows the results of the experiment and the simulation of high frequency transmission property to 1 GHz ~ 40 GHz, for the rectangular wire with resistivity of 3 x 10−6 ·cm, length of 4 mm, and width of 30 m. In the conventional inkjet wire formation, the high frequency transmission of the wire was difficult because the wires had dot configuration. However, in the wire formation by the laser-assisted inkjet technology, the theoretical calculation values and the actual values matched well, and the wire capable of high frequency transmission is easy to be realized.From the results of S11, slight discrepancies between the transmission gain of the calculated and experimental values was seen as the frequency increased. This is thought to be because the disorder on the wiring side of the coplanar transmission line pattern fabricated by the laser-assisted inkjet technology that may be affecting the impedance matching of the electromagnetic field. On the other hand, from the results of S21, good transmission property was obtained in the wire formation by the laser-assisted inkjet technology, since it was possible to transmit signals up to 40 GHz, and the attenuation was small up to about 10 GHz.From the above results, the possibility of high-speed transmission, which was considered difficult by inter-chip connection and wire bonding in the 3D mounting, was shown to be possible for the high frequency region at about 10 GHz using the laser-assisted inkjet technology.Fig. 9 High frequency transmission property of the formed wire(<40 GHz; blue – actual value; pink – theoretical calculation value))S11(dB)S21(dB)005101520253035400-20-20-15-10-10-5-30-40S11S21S21Frequency (GHz)4.3 Overcoming the step structuresTo check the possibility of formation to uneven surface and the control of the wet-spreading of ink on the rough-surface substrate with the laser-assisted inkjet technology, the wires were formed on a glass substrate ground in concave form with depth of about 200 m. Figure 10 shows the electron microscope image of the wire pattern formed on the stepped, rough-surface substrate. When laser assistance was not used and the substrate surface was very rough, the formed pattern was spread out significantly due to the capillary force in the in-plane direction of the unevenness on the substrate surface. Conduction was not obtained when the wire resistance was measured on both ends of the grinding groove.On the other hand, with laser assistance, there was no effect of the rough substrate surface, wire was formed having the same width in the stepped area, and conduction was obtained when the wire resistance was measured on both ends of the grinding groove. From these results, it was shown that the laser-assisted inkjet technology could be applied to the wire between the substrates with different wetness or lateral connection without using bump or fine through-via for the connection between IC chips.4.4 Improvement of adhesiveness of the wire by rough-surface substrateThe wire was formed by the laser-assisted inkjet technology on the mirror-surface and rough-surface substrates, and the adhesiveness of the wire was checked by the peeling test using cellophane tape, as indicated by the peeling test for plating (JISH8504). Figure 11 shows the results of the tape peeling test on the mirror-surface and rough-surface substrates.As a result, the wire on the mirror-surface substrate adhered to the tape, and the entire wiring peeled off the substrate. On the other hand, the wire on the rough-surface substrate did not peel off with the adhesiveness of the cellophane tape. From this result, it was indicated that the adhesiveness with the substrate could be increased if roughening treatment is applied to the substrate surface, due to the physical anchoring effect.Fig. 10 Wiring on stepped structure and rough-surface substrate(a) Without laser assistance (b) With laser assistanceFormed wireGlasssubstrateGrinding grooveFormed wireGlasssubstrate(a)(b)5kU×75200 µm45 22 SEI5kU×75200 µm48 22 SEI

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