Takeshi Kitadani

Fabrication of a Tapered Structure by Means of Exposure to Diffracted UV Light

Demands for personal digital assistants (PDA) call for them to be additionally low profile, lightweight, and low power. To fulfil these demands, it is necessary to develop a backlight unit that features low-power consumption, high brightness, and high efficiency. The light source in a backlight unit has a light guide plate, which is a highly important component. The light guide plate has dots to reflect light. It is known that the smaller the dots and the higher the aspect ratio, the brighter the screen. The result of a simulation revealed that it is possible to improve the brightness of light guide plate by forming the shape of a truncated cone with a taper angle of 68 to 78 degrees. However, using the existing machining technology, it is difficult to form the dots into such a shape. Producing a desired shape, like a tapered shape, in the depthwise direction is difficult even with lithography, although using an elaborate mask pattern, this technique can produce a sophisticated shape on a two-dimensional plane. We have produced a tapered microstructure with a high aspect ratio, devising an innovative method of diffracted light exposure based on a lithography technique making use of UV light source. Furthermore, we controlled the taper angle and fabricated a light guide plate through a mold master, Ni-electroforming, and an injection molding by using UV-LIGA process

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 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.