Ryosuke Mitsui

Continuous fine pattern formation by screen-offset printing using a silicone blanket

Screen-offset printing combines screen-printing on a silicone blanket with transference of the print from the blanket to a substrate. The blanket absorbs organic solvents in the ink, and therefore, the ink does not disperse through the material. This prevents blurring and allows fine patterns with widths of a few tens of micrometres to be produced. However, continuous printing deteriorates the patterns shape, which may be a result of decay in the absorption abilities of the blanket. Thus, we have developed a new technique for refreshing the blanket by substituting high-boiling-point solvents present on the blanket surface with low-boiling-point solvents. We analyse the efficacy of this technique, and demonstrate continuous fine pattern formation for 100 screen-offset printing processes.

A flexible proximity sensor formed by duplex screen/screen-offset printing and its application to non-contact detection of human breathing

We describe a flexible capacitance-type sensor that can detect an approaching human without contact, fabricated by developing and applying duplex conductive-ink printing to a film substrate. The results of our calculations show that the difference in size between the top and bottom electrodes of the sensor allows for the spatial extension of the electric field distribution over the electrodes. Hence, such a component functions as a proximity sensor. This thin and light device with a large form factor can be arranged at various places, including curved surfaces and the back of objects such that it is unnoticeable. In our experiment, we attached it to the back of a bed, and found that our device successfully detected the breathing of a subject on the bed without contacting his body. This should contribute to reducing the physical and psychological discomfort among patients during medical checks, or when their condition is being monitored.

Film-type connection system toward flexible electronics

A thin electric connector has been required for use in mobile electronics. Although an anisotropic conducting adhesive technology, e.g., the use of an anisotropic conductive film (ACF), has been developed to meet the demand, the technology is not suitable for flexible electronic devices based on plastic materials, since the plastic films used will change their mechanical properties by pressure and heat. To address these limitations, we have developed a novel film-type connector composed of a base material such as polyimide, an adhesive layer that deforms elastically against pressure, and electrodes arranged on the adhesive layer. In this study, the contact resistance of a film-type connector is investigated and compared with that of an ACF joint through four tests related to reliability. Results of the tests show that the film-type connector is more useful than the ACF joint in areas such as future flexible fine-pitch interconnections.

Simultaneous formation of fine and large-area electrode patterns using screen-offset printing and its application to the patterning on adhesive materials

Additive-type printing techniques such as gravure-offset printing and screen printing are effective for low-cost and ecofriendly electrode pattern formation. Gravure-offset printing is effective for fine pattern formation with widths on the order of 10–20 µm, whereas screen printing is effective for the formation of large-area patterns. However, it is difficult to simultaneously form fine and large-area patterns using these printing techniques. In this study, we demonstrate that fine (minimum width of 15 µm) and medium- as well as large-area patterns can be formed simultaneously using our developed screen-offset printing technique, which is a combination of screen printing on a silicone blanket and transfer printing from the blanket to a substrate. Furthermore, we demonstrate the application of our method to printing on adhesive materials, which allows electrode formation without applying heat to the film substrate.

Study on an interconnect technology toward flexible printed electronics

A reliability of a new film-type connection is investigated and compared to a conventional anisotropic conducting adhesive technology, e.g., an anisotropic conductive film (ACF) joint by measuring the contact resistance through environmental tests and flexibility tests. A film-type connector which thickness less than 0.1 mm is composed of a base material such as polyimide, an adhesive layer which deforms elastically against pressure, and electrodes arranged on the adhesive layer. Results of the test show that the film-type connection has some advantages compared to the ACF joint in mildness of the connecting condition and the contact resistance stability.

Development of a flexible interconnection and a preliminary study toward reducing package size

A reliability of a flexible interconnection using a film-type connector is investigated and compared to a conventional anisotropic conductive film (ACF) joint by measuring the change in contact resistance through folding tests. A film-type connector with thickness of less than 0.1 mm is composed of a base substrate, an adhesive layer which deforms elastically against pressure applied in a connection procedure, and electrodes arranged on the adhesive layer. Results of tests show that the flexible interconnection has some advantages compared to the ACF joint in contact resistance stability. A foldable connection technology has a possibility to make a contribution to future packaging.

Fine electrode pattern formation by screen-offset printing technique

We developed a new printing method called “screen-offset printing.” This method is the combination of screen printing and transfer printing techniques; ink is first screen-printed on a silicone blanket, and the ink is then transferred from the blanket onto a substrate. Such a procedure allows the formation of patterns with highly rectangular cross sections and finer patterns than can be achieved by conventional screen printing. In the present paper, we explain the details of this process and analyze its efficacy by comparing the experimental results of screen-offset printing with those of conventional screen printing. Further, we introduce a currently developing automated screen-offset printing machine and demonstrate the formation of fine patterns 20 μm in width.