Kenji Yamashita

Ni Electroforming of Large-area Micro Metal Molds

This study was carried out to evaluate the effectiveness of two kinds of organic hardening agents; saccharine sodium and sodium allylsulfonate, for increasing the surface hardness of nickel micro molds to be used in LIGA process. The authors prepared two kinds of plating solutions containing either one of these hardening agents in order to deposit nickel films from these solutions and measure the hardness of these films. As a result, the hardness of nickel-plated films obtained from the sodium allylsulfonate bath exhibited a hardness of 600Hv, which was extremely higher than that of the films obtained from the saccharine sodium bath. Following the above procedure, we heat-treated the nickel-plated films to evaluate their heat resistance. It was observed that the nickel films obtained from the saccharine sodium bath reduced their hardness at 250degC, while the films deposited in the sodium allylsulfonate bath maintained a hardness of 580Hv, demonstrating that these films hardly decrease their harness even when they are placed in a high temperature environment

Fabrication of Ultraviolet range Light Guide Plate

The light guide plate, as part of the backlight unit in a cell-phone or liquid crystal display, has evolved to meet market demands for low power consumption, high-luminance and high-quality displays. Along with the advance of the light guide plate, LEDs have undergone development as light source for light guide plates. Surpassing the limitations of LED emission in the visible light range, LEDs that emit ultraviolet light have been developed. In recent years, the ultraviolet light are used as a source of light of the air cleaner, and it is used as a source of light to activate the titanium oxide which is photocatalyst. Common ultraviolet light sources are either line or point light sources. There are no surface light sources capable of providing uniform lighting. The laboratory studies surface illuminators that incorporate diffusers in the visible light range. Applying our existing technology, we constructed an unprecedented ultraviolet surface illuminator (surface light source) and measured it using a photocatalyst. The experiment results are presented in this report.

Fabrication of large area X-ray diffraction grating for X-ray phase imaging

X-ray lithography, which uses highly directional synchrotron radiation, is one of the technologies that can be used for fabricating micrometer-sized structures. In X-ray lithography, the accuracy of the fabricated structure depends largely on the accuracy of the X-ray mask. Since X-ray radiation is highly directional, a micro-fabrication technology that produces un-tapered and high aspect ratio highly absorbent structures on a low absorbent membrane is required. Conventionally, a resin material is used as the support membrane for large area X-ray masks. However, resin membranes have the disadvantage that they can sag after several cycles of X-ray exposure due to the heat generated by the X-rays. Therefore, we proposed and used thin carbon wafers for the membrane material because carbon has an extremely small thermal expansion coefficient. We fabricated new carbon membrane X-ray masks, and these results of X-ray lithography demonstrate the superior performance.

Fabrication of High Performance Light Guide Plate and New Design for High Luminance

Recently, LED (Light Emitting Diode) is paid to attention as a new source of light. However, it doesn’t turn to shine on a wide area efficiently because LED is a point light. Then, the method of the light guide plate technology used for the liquid crystal display etc, and use as the LED lighting is examined. A minute reflection dots exists bottom of the light guide plate, system is such that light comes out from the surface because the light that hits the dots break a total reflection condition. In our laboratory, the function of the diffusion seat and the condensing prism seat that is complete parts of the lighting panel was involved by optimizing shape and the arrangement of the dots, and it works on the research of the light guide plate where uniform luminescence is enabled. In the process of study, it has been understood that luminance increases by increasing the number of dots, too. Therefore, an accumulating method of piling up two or more light guide plates was proposed as a method of achieving high luminance for highly effective lighting usage, and the device was analyzed with an optical simulator. As a result of optimization, the average luminance has improved by 15%. We are starting to fabricate this high luminance light guide plate by accumulating method. If this piled light guide plate is completed and luminance is improved in accordance with the simulation, it will be possible to convert it to a higher luminance light guide plate.Copyright

Examination of high luminance light guide plate by accumulating method

LEDs are attracting attention as a light source for a new form of lighting, taking the place of the fluorescent lamp and the light bulb. They are not suitable for lighting use by themselves, as LEDs are a point light source. However, it is possible to convert them into plane emission form by combining them with light guide plate technology used for the liquid crystal displays. It is therefore possible to use them as lighting devices through the plane emission method. In this laboratory, a minute dot was formed at the bottom of a light guide plate, and light hitting the dot was emitted from the luminescence side of the light guide plate. The amount of light emitted from the luminescence side also increased, if the number of these dots was increased from previous research results. It was thought that a high luminance plate or a plate guiding more light could be created. A method of piling thin light guide plates was proposed as a method of increasing the number of dots, with the piled light guide plates being designed using an optical simulator.

Fabrication of High Hardness Micro Mold Using Double Layer Nickel Electroforming

The LIGA is a total process for fabricating the metal mold of microstructure using deep X-ray lithography, electroforming a micro metal mold, and precise molding. This advantage is that it could reliably fabricate high-accuracy microscopic parts at a high speed and lower cost by using a micro mold to transfer a high aspect ratio pattern. Nickel electroforming is used as a fabrication technology of micro metal mold including LIGA process. However, neither the strength nor peelability of electroformed nickel is enough. A higher hardness is required for extending mold service life and improving the releasability of injection-molded parts. There are several methods to improve strength of metal mold alloying, and using additive composition agent of electroplating bath, for example. We obtained the surface hardness of 601 Hv at room temperature and 580 Hv even at 250degC using the sodium-allylsulfonate-containing high-concentration nickel sulfamate bath. But, an organic additive added to nickel plating bath has a stress decreasing effect. In this research, with an aim of increasing the hardness and relieving the internal stress of nickel micro mold, we have fabricated a 4 mm thick mold in two stages. One is a thin hard nickel layer deposited over the electroformed mold surface using an organic-additive-containing nickel plating bath. Another one is conventional nickel electroforming bath for producing warp free surface, thereby completing a double layer nickel micro mold.