Microlens Array Nickel Mold Core Micro-electroforming Process And Surface Quality Of Research

Polymer microlens arrays have been widely used in various high-technology fields, such as optical interconnection, detector arrays, image processing display, projector, scanners and digital cameras. Micro-injection molding technology is one of the main manufacturing methods for microlens arrays, due to its low cost, high efficiency and high automation. The mold insert with high quality is prerequisite for the fabrication of high quality microlens arrays by micro-injection molding technology. In this paper, the nickel mold inserts were fabricated by the micro-electroforming method. Taking the internal stress and the surface roughness as indexes, the effects of the rectangular pulse power parameters, (i.e. frequency, duty cycle and average current density) on the surface quality of mold insert was investigated. The optimized parameters, the influence sequence and the influenced law of parameters were obtained.Analyzing the principles of the pulse-current electroforming technologies, it was found that the pulse-current electroforming could transport the metal irons to the cathode in time, reduce the thickness of the diffusion layer, get the nickel mold inserts with fine grains and excellent mechanical properties. The author gave a brief introduction to the electrochemical theories during the micro-electroforming, mainly including the faraday's law, the theory of electrode potential and electrode polarization, the theory about the liquid transferring and the electro-crystallization of metal particles. Taking the theories as a guide, the author built the micro-electroformed platform and gave a detailed introduction to the each components. Regarding PS microlens arrays as a master and coating 500 nm copper film as conductive layer, nickel mold inserts were fabricated by micro-electroformed method under the condition of special electrolyte and some processing parameters.Taken the internal stress as a index, a series of micro-electroforming experiments were conducted to obtain the nickel mold inserts. Their internal stress was measured by X-ray diffraction. Designing orthogonal experiments, range method was used to analyze the experimental results. The optimized parameters for the rectangular pulse power and the effect sequence of parameters were obtained. Designing single factor experiments, the effects of parameters on the internal stress were obtained.Taken the surface roughness as a index, a series of micro-electro forming experiments were completed to get the nickel mold inserts. Their surface roughnesses and morphologies were measured and observed by the atomic force microscopy. Designing orthogonal experiments, range method was used to analyze the measured results. The optimized parameters for the rectangular pulse power and the effect sequence of parameters were obtained. Designing single factor experiments, the effects of parameters on the surface roughness were obtained.Taking the surface roughness as the first quality index and the internal stress as the second quality index, comprehensively considering the effect of rectangular pulse power parameters on the surface roughness and the internal stress of nickel mold inserts, finally the author got the optimized parameters. Under the conditions of frequency of 1000Hz, duty cycle of 24% and average current density of 1A/dm2, the nickel mold inserts of 3.53nm surface roughness and 79.25MPa internal stress were obtained.