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The field of printed electronics for highly integrated circuits and energy devices demands very fine and highly conductive electric interconnections. In this study, conductive lines having a high cross-sectional aspect ratio were printed via the inkjet printing of Ag nanoparticle inks assisted by a laser-induced selective surface wetting technique: a hydrophobic layer of self-assembled monolayer-treated ZnO nanorods was coated on a glass substrate and selectively ablated by a laser to form micro-channels for the inkjet, whose surface energy changed from 36.3 mJ/m2 to 51.5 mJ/m2 before and after the laser irradiation. With the varying width of the laser-ablated channels and pitch of jetted ink drops, the 3D shapes of the printed silver lines were measured to investigate their effects on the widths, heights, and uniformities of the printed patterns. The results showed that the present technique realized a uniform line of 35 μm width and 0.46 μm average thickness, having an aspect ratio of 0.013, which is 7.6 times higher than that printed on bare glass.

In this paper, we propose a unique micro multi-nozzle jet head to generate a stable column jet flow by applying vacuum suction to the side of a jetting nozzle. The micro multi-nozzle jet head was designed and fabricated to operate in both the jetting and suction modes selectively or simultaneously. The jet head includes eighteen jetting nozzles of 100 μm diameter, vacuum suction channels, inlets and a nozzle protection outer hole. The whole size of the micro multi-nozzle jet plate is 50 × 20 mm2. To demonstrate large area organic thin film coating, micro multi-nozzle jet coating was performed on a 5th generation size (1100 × 1300 mm2) glass substrate. A poly(3,4-ethylenedioxythiophene):poly(styrene sulfonate) (PEDOT:PSS) solution was selected as a test ink. To uniformly coat an organic thin film, we first investigated the physical parameter conditions such as jetting pressure, head suction pressure, stage moving speed, and coating head printing pitch. The thickness of the coated PEDOT:PSS thin film was 76.86 ± 3.33 nm and its uniformity (CV) was 4.33%.

In this paper, a bump-forming method for flip chip bonding using ink-jet printing technology is proposed. A flip chip bonded transmission line using ink-jet printed silver bumps consisting of conductive ink containing silver nanoparticles was fabricated to verify the electrical characteristics after the flip chip bonding process. The transmission line was designed according to microstrip theory for a frequency range of 300 kHz to 3 GHz, with the size of fabricated line being 35 (width) × 8.64 (length) × 0.5 (thickness) mm3. The electrical characteristics of a reference microstrip and the flip chip bonded line were compared with FEM simulation and measurement results. Direct current (DC) resistances of both the reference line and the flip chip bonded line were measured to be 3.1 Ω and 3.2 Ω, respectively. The discrepancy between measured insertion loss and the simulation result was only 0.04 dB at 3 GHz, and the return loss was greater than 15 dB in the measurement frequency range. As a result of the analysis, it was confirmed that the DC resistance of ink-jet printed bumps account for 0.56% of the total DC resistance, and the ink-jet printed bumps hardly affected the radio frequency (RF) characteristics of the RF transmission line at low frequencies. The results demonstrate that ink-jet printed silver bumps can be used for a simple and low-cost flip chip bonding process. We expect that the proposed method can be applied to the packaging of various electronics such as flexible, wearable devices and RF applications.

In this study, we introduce a thermal sintering process using a heated inert gas as a new sintering method. The heated gas flow is formed by passing nitrogen (N2) gas through a heating head of 300 to 700 °C, and the desired substrates are then exposed to the heated gas flow through a 400 mm long and 5 mm wide slit-nozzle. Sintering performance of Ag films was characterized by analyzing the electrical resistivity and metallographic structures according to the temperature change of the heating head. The temperature distribution of the heating region is analyzed by infrared (IR) thermal imaging and surface temperature measured by thermo-label tape. To test the feasibility of the proposed method for application to printed circuit board (PCB) manufacturing, we performed a reliability evaluation using the printed Ag patterns under the standard of the Institute for Interconnecting and Packaging Electronic Circuit (IPC), TM650. Various reliability test patterns were created by Ag inkjet-printing on both a rigid flame retardant 4 (FR4) substrate and a flexible polyimide (PI) film substrate. The reliability evaluation includes withstanding voltage, adhesive strength, thermal shock, pressure cooker, and bending tests. The surface wettability of the substrates was controlled to obtain high quality fine and uniform patterns by UV/O3 treatment after coating a fluoropolymer thin film.

In this Letter, a flip-chip bonding based on ink-jet printing technology is proposed and verified by interconnecting a separated coplanar waveguide (CPW) samples. Before the flip-chip bonding process, diameter and height of ink-jet printed silver bumps for flip-chip bonding are measured to be about 300 and 13 µm, respectively. In a frequency range from 300 kHz to 3 GHz, return loss and insertion loss of the flip-chip bonded CPW samples are measured to be higher than 20 dB and lower than 1.8 dB, respectively, where the length of the signal line is 35 mm. There are negligible discrepancies between radio frequency (RF) characteristics of the flip-chip bonded CPW and those of a conventional CPW. These results show that the proposed flip-chip bonding can be used to integrate RF components into electronic devices with low-loss using simple procedures.

In this paper, microstrip lines that are directly patterned by Ag ink-jet printing are discussed and their RF performance is investigated on both rigid and flexible substrates, which are FR-4 and polyimide (PI) film substrates, respectively. Microstrip lines are designed by computational simulation, and the simulated results are compared with the measured RF results of the fabricated microstrip lines. The measured transmission losses of the microstrip lines are 0.24 dB/cm for the FR-4 substrate and 0.66 dB/cm for the PI film substrate at 3 GHz. To measure the RF performance of the printed microstrip lines undergoing bending tests, the distances between the ends of the bended microstrip line are varied from 5 cm to 9.2 cm. The microstrip lines are twisted by torsion angles in the range of 0–40°. The RF performance and characteristics remain nearly unchanged under bending and torsion tests except for negligible variation caused by impedance mismatching occurred during the measurement process. The measured RF performance demonstrates that the printed Ag conductive lines can be utilized in RF application such as wearable and flexible systems, which require low-cost and low-end antennae at low frequencies.

We studied the effects of various plasma etching gases on a silver nanoparticle (AgNP) layer to find the proper etching conditions compatible with the AgNP printing process. An AgNP layer with thickness of 1.4 μm was prepared by spin-coating a AgNP suspension on a glass wafer; O2, CF4, and SF6 plasma were then individually treated on the AgNP layer for 1 min and for 10 min. The surface properties, elemental composition, and sheet resistance were measured in order to study the effects of plasma exposure on AgNP layer. Small particles and deposited materials were observed on the surface after treating with O2 and CF4 plasma, respectively, while large particles were grown by re-crystallization after SF6 plasma exposure. In summary, O2 plasma has the least damage to the AgNP layer, showing good surface properties and sheet resistance. CF4 plasma showed moderate results, and the SF6 plasma severely damaged the AgNP layer.

In this paper, we describe the analysis of inkjet-printed silver (Ag) patterns on epoxycoated substrates according to several reliability evaluation test method guidelines for conventional printed circuit boards (PCB). To prepare patterns for the reliability analysis, various regular test patterns were created by Ag inkjet printing on flame retardant 4 (FR4) and polyimide (PI) substrates coated with epoxy for each test method. We coated the substrates with an epoxy primer layer to control the surface energy during printing of the patterns. The contact angle of the ink to the coated epoxy primer was 69˚, and its surface energy was 18.6 mJ/m². Also, the substrate temperature was set at 70℃. We were able to obtain continuous line patterns by inkjet printing with a droplet spacing of 60 ㎛. The reliability evaluation tests included the dielectric withstanding voltage, adhesive strength, thermal shock, pressure cooker, bending, uniformity of line-width and spacing, and high-frequency transmission loss tests.

In this paper, nano-silver ink-jet printed transmission lines were fabricated to investigate RF performance on both flame retardant (FR-4) and polyimide (PI) as rigid and flexible substrates. The transmission lines were printed by using the ink-jet printer with velocity of 3.5 mm/s and were sintered in a convection oven with 250 °C. The RF performance of transmission lines was simulated and measured at low frequencies. The transmission loss is measured to be 0.22 dB@1 GHz and 0.32 dB@1 GHz, respectively, for the FR-4 and PI substrates, respectively. The return loss has over 16 dB for FR-4 substrate and over 12 dB for PI substrate. The RF performance of transmission line was investigated and discussed in regard to an influence by two substrates. The measured RF performance of fabricated transmission lines results in the possibility that flexible device is explored in low frequencies application.

A reciprocating pump operated by a piezoelectric linear actuator is introduced as a fuel supplying module for a DMFC. A series of experiments are conducted to characterize the performance of the present pump and effects of low reciprocating frequency pumping of fuel on output power of DMFC. The performance of the pump is studied with respect to reciprocating frequency and operating duty. The results show that the key advantage of the current pump is an ability of low frequency operation which enables high flow rectification performance and that power consumption of the pump is almost linearly proportional to the flow rate. It is also shown that the output voltage of the DMFC is stable with time even though the pumping pressure oscillates periodically

characteristics of silver inkjet printing were intensively investigated under control of surface energy and substrate temperature. A fluorocarbon (FC) film was spincoated on a polyimide (PI) substrate to obtain a hydrophobic surface, and an ultraviolet (UV)/ozone (O3) treatment was performed to control surface wettability of the FC film surface. To characterize the surface changes, we performed measurements of the static and dynamic contact angles and calculated surface energy by Wu's harmonic mean model. In silver inkjet printing, the hydrophobic FC film could reduce the diameter of the printed droplets. Merging of deposited droplets was observed when the substrate was kept at room temperature. Substrate heating was effective in preventing the merging phenomenon among the deposited droplets, and in reducing the width of printed lines. The merging phenomenon of deposited droplets was prevented also by increasing the UV/O3 treatment time.

The shape changes of inkjet-printed dots and lines were investigated by varying the primary solvent of nanosilver colloids, surface wettability and substrate temperature. The morphological changes in dots and lines in array patterns due to the interaction between neighboring dots or lines during evaporation was also examined for two different nanosilver colloids. In order to examine the effect of solvent evaporation rate, two different solvents with different boiling points (BP) were employed for nanosilver inks. With a fluorocarbon film coating and subsequent ultraviolet ozone (UV/O3) treatment, various surface wettability conditions were obtained on silicon (Si) wafers. Substrate temperature was varied from room temperature to 80 °C, and droplets from a 50 µm diameter nozzle were printed onto the substrate after optimizing the ejection of individual droplets. The results indicate that the shapes and sizes of dots and lines are sensitive to changes in both surface energy and substrate temperature, and the ink with a higher BP solvent produces larger dots under the same surface condition due to its slower evaporation. Dots and lines with better quality are achieved using the ink with a lower BP solvent. The morphological changes in dot and line arrays are dependent on the evaporation rate of the primary solvent as well as the distance between neighboring features. As a result, selecting a proper solvent for nanosilver ink is very crucial for controlling the shape and morphology of inkjet-printed patterns.

A reciprocating pump using a piezoelectric linear actuator is introduced as a fuel supply module for a direct methanol fuel cell (DMFC) stack. The results show that the key advantage of the pump with the linear actuator is its ability to operate at a low frequency, which enables high flow rectification performance. At the end of this study, the pump is applied to a DMFC system to demonstrate that the output voltage of a DMFC stack remains stable with time even when the pumping pressure oscillates periodically at frequencies of a few Hz. It is also demonstrated that the maximum output power of the stack exceeds 6 W with power consuming 3.5% of the stack power for the fuel pump.

The characteristics of silver inkjet printing were intensively investigated with control of surface energy and substrate temperature. A fluorocarbon (FC) film was spincoated on a silicon (Si) substrate to obtain a hydrophobic surface, and an ultraviolet (UV)/ozone (O3) treatment was performed to control the surface wettability of the FC film surface. To characterize the surface changes, we performed measurements of the static and dynamic contact angles and calculated the surface energy by Wu's harmonic mean model. The surface energy of the FC film increased with the UV/O3 treatment time, while the contact angles decreased. In silver inkjet printing, the hydrophobic FC film could reduce the diameter of the printed droplets. Merging of deposited droplets was observed when the substrate was kept at room temperature. Substrate heating was effective in preventing the merging phenomenon among the deposited droplets, and in reducing the width of printed lines. The merging phenomenon of deposited droplets was also prevented by increasing the UV/O3 treatment time. Continuous silver lines in the width range of 48.04–139.21 µm were successfully achieved by inkjet printing on the UV/O3-treated hydrophobic FC films at substrate temperatures below 90 °C.