Key Engineering Materials Vols. 364-366

Abstract: The laser ablation technique is one option for micro-machining and patterning of diamond film. A UV YAG laser with higher energy density can remove or destroy the diamond film more efficiently than the excimer laser. That is, the UV YAG laser not only provides faster etching rate on the diamond film, but also requires less processing and maintenance cost. In the current study, synthetic diamond films with grain size of 30 μm were deposited on silicon substrate by microwave plasma enhanced chemical vapor deposition (MPCVD) in the CH4/H2 mixture atmosphere. A pulsed UV YAG laser (λ = 355 nm, 10 kHz) was employed to machine and remove the diamond film. The diamond film surface was analyzed by SEM and Raman spectroscopy after the laser machining. The beam size of YAG laser was adjusted to between 0.1 mm and 1.5 mm by the trepan mechanism to approach the following defined scanning width. In order to shape a 4-inch diamond wafer into a microstructure, the scanning width of the UV YAG laser was defined to 0.1 mm, 0.75 mm and to 1.5 mm in several loops. The results show that the laser-polishing effect can be applied to the pretreatment of mechanical polishing of diamond wafer in the condition of 0.75 mm scanning width in 3 loops. From Raman spectrum, it could prove the mechanism of carbon burning reaction during the laser processing and the residual carbon existing in the laser-patterned area. The surface of diamond film is strongly affected by the laser processing and a better result from the parameter of 0.75 mm scanning width in 3 loops is shown in the current study.

Abstract: Chip on glass (COG) bonding using Anisotropic Conductive Film (ACF) is the best process for assembling ICs on thin substrate glass with fine pitch in current practice. This paper investigates the effects of surface cleanness of the substrate, bonding pressure and contact area of COG bonding with ACF on interfacial impedance (II) via experiments. Indium tin oxide (ITO), 350±15nm in thickness, coated on 0.4mm glass is used as the substrate with φ4μm ACF particle in the experiment. Surface cleanness is measured by wetting tension, an alternative measurement of surface energy. Experiments with three levels for each parameter are designed and conducted. Reliability tests, including temperature test, humidity test, cycling test and boiling test, are also conducted to allocate best parameters in the COG bonding process. Experimental results showed that the contact area of ACF must be more than 1,500μm2 in order to provide stable II. Surface cleanness of ITO glass is suggested to be higher than 46 dyne/cm as measured by wetting tension test. Bonding pressure, ranging from 40 to 80 Mpa, does not have strong effect on II. Temperature test under -40°C /30min to 85°C/30min at 120cycle and humility test at 85°C under 85%RH for 500 hours showed that higher surface cleanness results in better bonding result as the variation of II is lower. Boiling test at 121°C under 2atm for 8 hours showed that surface cleanness should be over 46 dyne/cm, as measured by wetting tension test, to ensure stable bonding result.

Abstract: Employment of rotary ultrasonic machining (RUM) technique to mill glass material was attempted in this research. The feasibility and efficacy of the novel milling process were evaluated. The challenge of the attempt in the present study had to do with the fact that the direction of RUM tool oscillation was inherently perpendicular to the direction of milling. The RUM apparatus employed for the study comprised a computerized feeding system, a drive control system and an ultrasonic oscillation system. The RUM system was also characterized by having a feeding system fit for a PC-controlled stepping motor. It was found that the oscillation associated with the RUM milling was effective in reducing the machining resistance encountered during milling process, making it possible to increase the feed rate and thus the material rate, as well. However, the increased milling depth and feed rate would have an adverse effect on the tool life in terms of more breakage of grinding grits on the tool, thus resulting in faster wear rate of the milling tool.

Abstract: This research applies 3D mesh mold-flow analysis to analyze the SD (Secure Digital) card. It aims at temperature of the mold and plastic. The proper mold filling temperature is found by simulation analysis to improve the short shot situation, and seeks the cause of warping via various processed conditions. SD memory card clip has a big variation in thickness. Due to the bigger flow resistance the plastic is difficult to reach thinner portion, even hot plastic is also difficult to supply. The temperature of plastic goes down as a result of the cold mold cavity. Thus, the plastic does not reach certain portions before solidifying. The cooling system of injection machine was controlled by constant temperature oil cooling. This study explored the optimum injection condition by utilizing experiment to control the temperature of the plastic, the temperature of mold, the packing pressure process and so on. It is valuable to companies which utilize injection mold applications.

Abstract: Chips scraping each other during transportation, and chips coming into contact with water or air will cause oxidization resulting in poor quality products. The chips need to be well packed and to be protected from the environment. The method of Surface Mount Component (SMC) packing using plastic carrier tape can reduce chip damage. This study focuses on the extrusion process parameters optimization of plastic carrier tape. Because each extrusion process produces 270 pieces of carrier tape, the tape size is 1.35mmX2.25mmX1.35mm and is extremely difficult to reach the tolerance standard. This study utilized a practical test to explore various factors on the quality of the carrier tape, such as the rotational speed of extruder screw motor and extrusion mold; the negative pressure of extrusion mold; and the temperature of the extrusion mold. These experiments could find out an optimal extrusion process.

Abstract: Hard turning has the advantage of rapidly, elasticity and low energy consuming. It has been a trend to replace the complex grinding processes, especially for small batch machining.The surface roughness value of steel after being grinded will ranged in 0.1 to 1.6 μm Ra. This paper points to the precision hard turning of the hardened mold steel, seeking the cutting conditions that can be received in the surface roughness value below 0.1μm Ra, in order to replace the grinding processes. The precision dry turning test were conducted with ceramic cutting tools. The nose radius of the cutting tool was 1.2 mm and the depth of cut was fixed at 0.05 mm. Through a series of turning test, it can be found that, when cutting speed was at 80 to 200 m / min, and feed rate at 0.005 to 0.009 mm / rev, the surface roughness value would be all below 0.1μm Ra. It was superior to grinding process. So we can say that, it is possible to replace the grinding process by hard turning when machining the hardened mold steel.

Abstract: High ductility, high strength, high work hardening rate and low thermal conductivity of stainless steels are the main factors that make their machinability difficult. In this study, determination of the optimum cutting condition has been aimed at when fine turning an AISI 304 austenitic stainless steel using ceramic cutting tools. The cutting speeds for the turning test were from 80 to 320 m / min, feed rates were from 0.04 to 0.10 mm / rev and the depth of cut was fixed at 0.1 mm. According to the test results, we can find that the values of surface roughness were decreased when the cutting speed was increasing, and decrease with the decrease of feed rate. But when the cutting speed was greater than 360 m / min, or the feed rate was smaller than 0.02 mm / rev，the surface roughness would be deteriorated because of the chatter phenomenon. In this paper, a polynomial network is adopted to construct a prediction model on surface roughness for fine turning of AISI304 austenitic stainless steel. The polynomial network is composed of a number of functional nodes. These functional nodes are self-organized to form an optimal network architecture by using a predicted square error (PSE) criterion. It is shown that the polynomial network can correctly correlate the input variables (cutting speed and feed rate) with the output variable (surface roughness). Based on the surface roughness prediction model constructed, the surface roughness of the workpiece can be predicted with reasonable accuracy if the turning conditions are given and it is also consistent with the experimental results very well.

Abstract: The Taguchi method is regarded as a powerful tool to design optimization for quality. In this study, it was used to find the optimal cutting parameters for precision-drilling operations. The cutting parameters include guiding drilling, spindle speed, feed rate, stepping amount, number of steps and cutting fluid. The considered characteristics of performance are tool life, and the variation of drilled hole-diameter. Taguchi Method and Orthogonal Array were applied to the experiments of precision-drilling so as to allocate the corresponding processing parameters. The obtained results were then evaluated by Response Table, Response Chart, and Analysis of Variance methods (ANOVA) to acquire the optimal processing parameters. These were further confirmed by experiment. Finally, the analysis of the precision-drilling process applied for mold steel SKD61 shows that this approach can greatly improve the drilling performance of a small-drilling process.

Abstract: The glass molding process is considered to have a great potential for the mass production of aspherical glass lenses with high precision and low cost. However, glass molding has a serious problem of mold sticking with glass which needs to be resolved. This research investigates the interface reaction between glass and mold by high temperature wetting experiment, which provides the reference for the designing anti-stick coatings. The SUMITA K-PSK200 optical glass gobs with low Tg were used in this study. The influence of operation temperature, ambient gas, substrate materials, and thin film composition on wettability of glass at high temperature were studied. The results show that the higher the temperature, the smaller the wetting angle between glass gob and substrate could be observed. This indicates that severe interface chemical reaction occured and resulted in the loss of transparency in glass appearance. The wetting experiment in nitrogen ambient improved the sticking situation. The combination of chemically stable substrates and coatings, such as Sapphire (substrate) / GaN (film) and Glass (substrate) / Al2O3 (film) can achieve the best antistick propose. The precious metal films, such as Pt, Ir, coated on the ceramic substrates can effectively reduce the interface reaction between the glass and substrates.

Abstract: Recently, ultra-precision micro patterns and shapes have been widely used in optical field. Various methods which are based on semi-conductor fabrication methods are nowadays used in fabrication of micro shapes and patterns, but micro endmilling technology has lately attracted considerable attention because of various available materials, flexibility of process and high-productivity. For the precision micro endmilling process, analysis of micro cutting error is mandatory. In general, tool deflection is a major factor which causes cutting error and limits realization of the high-precision cutting process. Specially, in micro endmilling process, micro tool deflection generates very serious problems compared to macro tool deflection. In this paper, it is performed to observe the real tool deflection shapes in micro endmilling process, so the trend of micro tool deflection was analyzed using real captured images in this study. To get the real images of micro tool deflection, micro slot cutting processes were executed under various cutting conditions using micro endmill and the real images of tool deflection were obtained during cutting process by high-speed camera. Finally, the extent of tool deflection was calculated by the deflection angle according to cutting conditions and two trends (the point of first tool contact and the cutting stage) of micro tool deflection were analyzed.