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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 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.

This study proposes the unique method to analyze the cleanliness of the fine metal mask (FMM) used in OLED display manufacturing after FMM cleaning process. We developed a FMM-mimic microstructure as a substitute for the FMM, which can be used for the evaluation of cleaning efficiency. The FMM-mimic microstructure was fabricated using a combination of photolithography, reactive ion etching, anodic bonding and sand blasting processes. To demonstrate the proposed cleanliness analytical method, a 1.4 μm-thick Tris-(8-hydroxyquinoline) aluminum (Alq3) film was deposited on the FMM-mimic microstructure as a contaminant by vacuum thermal evaporation. The Alq3-deposited FMM-mimic microstructure was cleaned by N-methyl-2-pyrrolidone (NMP) with changing cleaning time. We analyzed the residual contaminants on the FMM-mimic microstructure using a fluorescence microscope. The developed FMM-mimic microstructure proves very convenient for inspecting the residual contaminant inside the gap through the transparent glass by general optical and fluorescence microscopy.

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, 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.