Advanced Materials Research Vol. 797

Abstract: Glass panels are one of core components in liquid crystal displays (LCDs). Grinding is an essential edge chamfering process in the preparation of LCD glass panel. With the size of glass panel increasing, both high productivity and high quality are required in the edge chamfering process. However, surface and subsurface defects are usually introduced to the chamfered glass edge under high-efficiency grinding conditions. In this work, we explored to develop crack-free grinding process while maintaining high chamfering efficiency with two designed diamond wheels for the chamfering of LCD glass edges. The grinding performance was compared and analyzed in terms of surface roughness and morphology. Normal and tangential grinding forces were measured to characterize the material removal characteristics. It was found that crack-free grinding/chamfering of LCD glass edge was achieved under high-efficiency grinding conditions i.e. wheel speed of 52.3 m/s, feed rate of 10 m/min, depth of cut of 50 μm. The developed grinding process is potential to reduce subsequent polishing time and cost or even replace subsequent polishing process for the preparation of LCD glass edge.

Abstract: t is known that cutting force is the key to reasonably select cutting parameters, and the base to study the cutting mechanism. Genetic Algorithm and multiple regression analysis were adopted to achieve cutting force predicted model of multi-diamonds fast milling hard-brittle materials with defined diamond grains pattern by single diamond fast milling hard-brittle materials experiments. Results show that cutting force predicted model by genetic algorithm has higher precision than that model by multiple regression, and the cutting force prediction method based on genetic algorithm is more suitable for those hard-brittle materials which components are relatively soft and simple. Predicted model can afford another study direction for processing analysis of diamond tools, tools making and processing parameters selection from the view of diamond grain practice cutting.

Abstract: As a typical multi-functional single crystal material, Lithium tantalate (LiTaO₃ or LT) exhibits its excellent electro-optical, pyroelectric and piezoelectric properties, and has now been widely applied into many applications, especially in the telecommunication field. However, the most critical issue in the process is its pyroelectric effect and piezoelectric effect which potentially leads to crack initiation during grinding. Because it is rich in plasticity, LT demands larger specific energy for material removal. As the most machining energy is eventually converted into heat, LT undergoes a rapid rise in temperature during the grinding process, thus highly risks in thermal shock. In order to clarify the thermal influence on the grinding process of LiTaO_3, the effects of coolant temperature, diamond grinding wheel geometry and material of substrate are investigated in this research. The experimental results show that the increasing rate of grinding torque (or force) and surface roughness are two major factors dominating the crack initiation during grinding of LT wafers. Via a DOE (design of experiment) analysis, coolant temperature and wheel type stand out as the main factors influencing on the increasing rate and wafer surface roughness.

Abstract: In this paper, according to the slurry ingredients obtained by former research, the influences of the chemical mechanical polishing (CMP) process parameters, such as the rotational velocity of the platen and the carrier, the polishing pressure and the abrasive size on the material removal rate (MRR) and surface roughness Ra have been studied in CMP SiC crystal substrate (0001) C and (0001) Si surface based on the diamond abrasive. The research results show that the material removal rate changes with the change of the abrasive size, the rotational velocity of the platen and the polishing pressure significantly, but the maximum of MRR can be obtained at a certain rotational velocity of platen, abrasive size and polishing pressure. The influence of the abrasive size, the platen velocity, the carrier velocity and the polishing pressure on surface roughness is no significant. Under the same conditions, the MRR of CMP the Si surface is larger than that of the C surface. This study results will provide the reference for optimizing the process parameters and researching the material removal mechanism in CMP SiC crystal substrate.

Abstract: To enhance polishing quality, polishing efficiency and improve the backward state based on single-process way for function ceramics in CMP, a new optimization method of process parameters based on multi-process and multi-evaluation theory is put forward. Firstly, based on experimental data obtained from orthogonal experiment, the optimal combinations of process parameters are got separately in term of surface roughness and material removal rate, which is optimized by Taguchi method in each process. Secondly, combining analysis of evaluation index weight ratio with analysis of variance, the final optimal combination of process parameters is received under the integrated evaluation of surface roughness and material removal rate. Finally, the contrast verification results show that the proposed optimization method is effective.

Abstract: The purpose of this paper was to investigate the silicon wafer surface roughness ground by the micro pellet grinding tool and the electroplated disc grinding tool with diamond grit size of 4-6 μm and 10-20μm under the spindle rotation speed of 500-2500 rpm and the feed rate of 1-5 μm/min. The results showed that the micro pellet grinding tool can get a better surface roughness of the silicon wafer than the electroplated disc tool. When the tools containing a larger diamond grit were employed, selecting a higher spindle rotation speed and a lower feed rate can obtain a better wafer roughness. However, when the tools of a smaller diamond grit were used, the spindle rotaion speed operates properly at a optimal value to obtain a best wafer surface roughness, which achieves Ra = 0.03-0.06 μm for the micro pellet tool. Besides, the material removal mechanism during the grinding silicon wafer for these two tools displayed mainly ductile grinding behavior.

Abstract: Diamond conditioners, or dressers, are commonly used to dress polishing pads that are applied to the chemical mechanical polishing of silicon wafers for integrated circuits. Although the diamond conditioner has regular distribution diamond grits, they differ in shape and can be oriented differently because the shape of diamond grits is generally cubo-octahedral. Therefore, the dressing behaviors on the polishing pad are unpredictable. In this work, the fundamental characteristics of dressing are investigated by a single crystal diamond with various shapes (each resulting in point-cutting, line-cutting, and face-cutting), a rake angle of-50°, and cutting faces in the (100) and (111) planes. For the purpose of analysis, plowing ratio is defined as the sum of the areas of the two side ridges divided by the groove area. This ratio can be used to evaluate the contribution of plowing and cutting actions from the dressing. Experimental results reveal that a groove with ridges on both side walls is formed as the diamond is moved over the pad. The profile of the scratch correlates with the shape of the diamond. In summary, cutting dominates when point-cutting is responsible for the dressing. On the contrary, plowing plays a major role with respect to line-cutting. The cutting action tends to dominate when the dressing is completed by face-cutting a (111) plane. Alternatively, the wear tends to be dominated by the plowing action if the dressing is conducted via face-cutting a (100) plane.

Abstract: The growth of epitaxial layer of SiC wafer requires the surface of SiC substrate to reach an atomic scale accuracy. To solve the problems of low machining efficiency and low surface accuracy in the polishing process of SiC wafer, a novel ultra-precision machining method based on the synergistic effect of chemical reaction and flexible mechanical removal of the magnetorheological (MR) effect, the MR-chemical mechanical polishing (MRCMP) is proposed. In this technique, magnetic particles, abrasives and chemical additives are used as MR-chemical polishing fluid to form a cluster MR-effect flexible polishing platen under an applied magnetic field, and it is expected to realize an atomic scale ultra-smooth surface planarization with good controllability and high material removal rate by using the flexible polishing platen. Polishing experimental results of C surface of 6H-SiC crystal substrate indicate that an atomic scale zero-defect surface can be obtained. The surface roughness of C surface of SiC wafer decreased from 50.86nm to 0.42nm and the material removal rate was 98nm/min when SiC wafer was polished for 60 minutes.

Abstract: Green manufacturing is important subject. In order to reduce waste disposal cost and environmental load, decreasing machining fluid that contains several chemicals such as oil, extreme pressure agent etc. is demanded. In this investigation, the electric rust preventive machining method system that uses only water as machining fluid have been developed. This paper mentioned about evaluation of recycled water quality. The refined water that is purified with developed water recycle system which is installed reverse osmosis membrane (RO) is too clean to evaluate by normal method till now. Using laser turbidity meter, precise water purification is evaluated precisely. Therefore, it is clarified that RO refined water turbidity (RO1=0.0006, RO2=0.0003) is very low compared with clean tap water (0.1207). So, water recycle system can remove contaminating fine particle from water. It is expected that scratch less ultra precision machining with water is enabled to conduct with high filtration ability.

Abstract: The grinding process has particular interest in that contact temperatures have great significance for quality and integrity of machined surfaces. Hardened surfaces may be damaged by softening and or being stressed, being hardened or re-hardened, burned or cracked. It is important in grinding for the fluid to remove heat from the grinding contact zone to avoid thermal damage to the workpiece surface and/or sub-surface layers. The cooling effect of grinding fluid can be quantified by the convective heat transfer coefficient (CHTC) acting in the grinding zone. This paper presents values of the CHTC based on measured grinding temperatures. The paper also presents a new convective heat transfer model based on principles of applied fluid dynamics and heat transfer. Predicted values for the CHTC calculated from the model are compared with results from experiment obtained under a range of grinding conditions and with experimental data. The results demonstrate that the new CHTC model improves the accuracy of prediction and helps explain the variation in the value of CHTC under varying process conditions. Results also show that convection efficiency strongly depends on the grinding wheel speed, grinding arc length and fluid properties.