Papers by Author: Ren Ke Kang

Abstract: Ultrasonic assisted grinding (UAG) has been a promising solution for the machining of brittle materials. The vibration amplitude in UAG has significant influence on the machining process. In this paper, the experiments which apply UAG process on K9 glass were conducted to investigate the effect of amplitude upon grinding force and surface roughness. Theoretical calculation was done to explain the phenomenon observed and to analyze how vibration affects the grinding process. The conclusion is reached that the vibration amplitude should be cogitatively set to achieve better surface quality while realizing the reduction of the grinding force.

Abstract: Material removal rate (MRR) distribution is a major concern in CMP process. In the published literatures, both experimental and theoretical research, MRR distribution is given without considering the surface profile of wafer. In this paper, the effect of surface profile on the MRR is analyzed based on the Preston equation and the contact pressure distribution calculated by the mixed lubrication model. It is found that the MRR distribution is dramatically affected by the profile of wafer surface, and whatever the polishing pad is conditioned in situ, the MRR distribution will be uniform at last. In addition, the wear of the pad surface induces a decrease of MRR.

Abstract: Due to the requirements of on-line detection of grinding force in the grinding process, this paper utilizes the structural characteristics of ultra-precision grinder with double-spindle and single-workstation, and then presents a grinding dynamometer based on piezoelectric effect of quartz crystals. Besides, the grinder dynamometer can measure grinding force in three directions, and the static properties of dynamometer are experimentally tested in a special experiment table. Moreover, the on-line static calibration and the actual grinding experiment of dynamometer installed in the silicon wafer grinder are performed. The results indicate that the grinding dynamometer has satisfactory static properties, that is, the linearity and repeatability are less than 1%, and the cross-talks are also less than 5%. As a result, each indicator has full reached the operating requirements in using of large diameter silicon wafer grinding force measuring.

Abstract: The machining methods such as waterjet cutting, milling, grinding, lapping, etc. are usually used to manufacture glass fiber reinforced composites (GFRCs) parts. Damages will be produced unavoidably in the machining process, no matter which machining method is employed. Subsurface damage is one of the important parameters to evaluate the surface layer damages. The detection method for the subsurface damages of glass fiber reinforced glass matrix (glass/glass) composite after machining is researched. The characteristics of subsurface damages of glass/glass composite after waterjet cutting, milling, grinding and lapping are investigated mainly, when the fiber direction is either perpendicular or parallel to the cutting surface.

Abstract: Wire saw process is widely used in the machining of hard and brittle materials with low surface damage and high efficiency. Cutting of silicon wafers in integrated circuit (IC), semiconductor and photovoltaic solar industries is also generally using wire saw process. However, the surface layer damage induced by wire saw process will seriously decrease the wafer quality and increase the process time and production costs of the post grinding and polishing. The surface layer qualities of the silicon wafers sawed by the different wire saw processes was investigated in this paper. The characteristics of surface roughness, surface topography and subsurface damage of silicon wafers sliced by the fixed abrasive and the loose abrasive wire sawing respectively were compared and the corresponding reasons were analyzed.

Abstract: Superalloys are widely used in the aeronautic and astronautic industries owing to their excellent properties in aspects of high-temperature strength, heat stability and thermal fatigue resistance. However, the severe loading of grinding wheel and the poor integrity of grinding surface usually become the problem in grinding of superalloys with conventional grinding wheels. In this paper an experimental study was carried out to investigate the grinding characteristics of superalloys with microcrystalline alumina abrasive wheel. The roughness of grinding surface was tested, on which the effects of the grinding parameters were analyzed. Study results indicated that low loading of grinding wheel and high quality of grinding surface (Ra 0.2 μm) were obtained. The grinding parameters were optimized based on the experiment results.

Abstract: Larger diameter wafers are used to decrease the cost of IC manufacturing and the wafer thickness is decreasing for form factor and thermal power dissipation considerations. The larger wafer requires a large scanning area to inspect the warp, and warp measurement of large and thin silicon wafers is greatly affected by the gravity-induced deflection. In this paper the gravity-induced deflection was calculated using finite element method by supporting the wafer horizontally with three steel balls. A laser displacement sensor based on triangulation principle was used to measure the warp and an air bearing stage was developed to achieve high straightness. The shape of the wafer was obtained using the silicon wafer warp measuring equipment.

Abstract: The surface integrity of the machined components of the high volume fraction SiC particle reinforced Al composites (SiCp/Al) is important as it influences the performance of the part. The grinding experiments of 55% volume fraction SiC particles reinforced Al composite with and without ultrasonic-assisted were performed. The grinding forces were tested, on which the effects of the grinding parameters were analyzed. The surface topography of SiCp/Al after ultrasonic assisted grinding were observed, based on which the material removal mode was discussed.

Abstract: A simulation framework based on the mixed elastohydrodynamic lubrication (mixed EHL) model has been used successfully to explain some phenomena observed in Chemical mechanical polishing (CMP) process. However, the pad deformation model adopted in various CMP simulation frameworks, such as Winkler elastic foundation model or elastic half-space model, can not correctly describe the deformation features of pad, especially at the wafer periphery. In this study, a layered elastic theory, which can calculate the pad deformation with similar accuracy but lower computational cost than 3D finite element method (FEM), is introduced into the mixed EHL, and it is significant to predict the contact pressure distribution more accurately than existing approaches. Further, the material removal rate can be predicted accurately, it is useful for the study of the mechanism of CMP and the optimization of the CMP processing parameters.

Abstract: In order to improve the surface quality of sapphire substrates ground by diamond wheel, the chemo-mechanical grinding (CMG) tools for sapphire grinding was investigated in this paper. According to the processing principle of CMG, three CMG tools with different abrasives of SiO2, Fe2O3 and MgO were developed respectively. The compositions of the CMG tools were designed and optimized based on the physicochemical characteristics of sapphire. The grinding experiments were performed with the developed CMG tools and the grinding performance of three kind of tools were evaluated by comparing the surface roughness and the MRR of sapphire. The experiment results show that the grinding performance of SiO2 CMG tool was worst. The surface roughness and MRR corresponding to SiO2 CMG tool were all significantly poorer than Fe2O3 and MgO CMG tools. The highest MRR could be obtained by Fe2O3 CMG tool, but the best surface quality was obtained by MgO CMG tool.