Characterization of SUS Molds for light guide-plates by electro-chemical fabrication (ECF) method

Abstract

A new micro fabrication method termed electro chemical fabrication (ECF) is introduced to overcome conventional problems of electrochemical machining (ECM), such as low reliability and reproducibility. This ECF process defines micro patterns using a conventional photolithography, allowing it to produce microscale patterns with an excellent surface profile and of excellent quality. In this paper, four-inch 304 SUS and Ni molds were fabricated by using ECF and FeCl3 wet etching processes, respectively. The etch rate of stainless steel was measured at nearly 0.27 mu m/min at optimized ECF conditions and that of Ni was 0.77 mu m/min with FeCl3 dipping. To ensure a uniform depth profile of 10 mu m, the process time for the SUS and the Ni mold were determined to be 36 minutes and 13 minutes, respectively. After the fabrications of SUS and Ni molds, the ECF-SUS mold showed two times better surface roughness values than the FeCl3-Ni mold. To evaluate the ECF-SUS process, light guide plates (LGP) were made using an injection molding method. The LGP using the FeCl3-Ni mold showed a hazy area when tilting the plate. This haze effect is believed to have formed from poor surface roughness. An LGP made with an ECF-SUS mold showed a 25% higher brightness and a 15% higher light uniformity compared to a FeCl3-Ni mold.