Key Engineering Materials Vols. 359-360

Abstract: Silicon wafer is one of the key materials of LSI and SLSI and has been widely used in the electronic industries and IT products. In the new century of nano times, silicon wafer needs higher geometry accuracy, lower surface roughness and higher precision machining effecency, but no disfigurement in its surface layer. Nowadays, non-contact polishing still seems to be most efficient method to achieve nano-scale geometry accuracy and maintain surface roughness in the nanometer level even for silicon wafer, but it is still not easier to control its machining course and to obtain well-pleasing machining effecency. In this paper, a hydrodynamic electro-chemical polishing system based on CNC is established with micro-displacement compensating for nano-scale polishing. A new type of compliant polishing tool system is developed, which can turn orthogonal force control subspace and position control subspace to isomorphic position servo space. Moreover, it convert force control deflection to position servo deflection and in this way the polishing force is controlled by micro-displacement compensating with piezoelectricity. Polishing experiments on silicon wafer, in hydrodynamic polishing fluid mixed with nano-scale SiO2 abrasive particles, have been conducted to investigate the fundamental machining mechanism.

Abstract: In the paper, a new method of using rotating magnetic field generated by a stator of alternative electromotor to polish the inner surface of tube-type workpieces is proposed; a finishing device using the stator construction and inverter is designed; the finishing mechanism is analyzed and experiments are carried out. Experimental investigations show that filling amount of magnetic abrasive influences the surface roughness of workpiece directly and have an optimal value. The higher magnetic conductivity is, and the finer finishing effect is. The attraction force of magnetic particles depends on intensity of magnetic induction directly and has the optimal value. The higher the rotation speed is, and the lower the value of surface roughness. Under the optimal experimental condition, the new method can reduce the value of surface roughness more than 2 grades. Therefore, this technique has prospective application future.

Abstract: Magnetic Abrasive Finishing (MAF) is relatively a new finishing technique which employs the magnetic force for finishing. In this paper, the influence of the magnetic flux density on the finishing pressure and the finishing efficiency during finishing is analyzed. With the cylindrical magnetic finishing apparatus developed by the author, a series of experiments on finishing the cylindrical surfaces of nonferromagnetic materials and ferromagnetic materials are carried out. To solve the problems of low finishing efficiency and abrasive particles escaping easily because of lack of finishing pressure during finishing nonferromagnetic materials, a new method of increasing the finishing pressure by using the “pressure-increasing bag” in the finishing system is put forward. A lot of comparative experiments on finishing nonferromagnetic materials with the “pressure-increasing bag” and without the “pressure-increasing bag” are performed. Under the same experimental conditions, the amount of diameter-reduction
d is increased from 1μm to 1.88μm and the surface roughness is improved from Ra0.315μm to Ra0.250μm by using the “pressure-increasing bag”. The results show that the finishing pressure is increased obviously and the MAF efficiency of finishing nonferromagnetic materials is improved dramatically by using the “pressure-increasing bag”.

Abstract: During the transferring process of the large die surfaces, there are extensive needs of die surface polishing. Since almost large die surfaces are free-form surfaces, currently, these are almost manually implemented. In order to overcome this barrier, base on design a floating polisher, this paper focuses on polishing rule of floating three polishing disks and the optimization of the associated polishing process parameters. In order to enhance the polisher performance, affecting factors of polishing process, including the rotation speed of polishing discs, normal acting force on polishing disc, loci of polishing disc movement, feeding rate of polishing disc, grit of abrasive particles, and inclined angle of the acting force on disc, are synchronized and analyzed versus roughness of polished surfaces. Then, using the parameter design plans and conducts tests regarding these affecting factors. Finally, the floating polishing process parameters are optimized based on the test results. These optimized results are used as operating guides for applications of the floating die polisher.

Abstract: Polishing pad plays a key role in determining polish rate and planarity of a chemical mechanical planarization (CMP). The properties of the pad would deteriorate during polishing because of pad surface grazing, which results in reduced removal rates and poorer planarity of wafer surface. Pad conditioning and its influence on pad surface structure and CMP process is introduced and discussed in this paper. The study shows that the surface structure can be regenerated by breaking up the glazed areas with conditioner, MRR(Material Removal Rate) can be maintained at high level with proper pad conditioning, and UN(Non-uniformity)can also improved. Orthogonal experiments design is employed in this study to determine the best conditioning parameters.

Abstract: Dual rotation plates lapping method can effectively solve the limitations of traditional ceramic ball machining methods. This paper focuses on the application of Taguchi method to optimize the technique parameters to lap ceramic ball. The main objective is to study impact degree of the process parameters (lapping load, lapping speed combination and slurry concentration). The results show that the experimental design based on Taguchi method can determine the optimum machining conditions which improve the surface quality and geometrical precision of ceramic ball.

Abstract: Chemical vapor deposited (CVD) diamond film is a good materials for cutting tools as its a series of excellent properties. But because of its polycrystalline morphology, CVD diamond thick film has a rough surface that limits its application in engineering. In this paper, study was carried out on the mechanical lapping of diamond film. It is shown that surface roughness of the film was reduced from Ra 4.5μm to Ra 0.2μm after 50-minute polishing. The surface integrity of polished diamond thick film was investigated, which includes surface roughness, morphology and residual stress. There are a lot of micro defects such as grooves, gas cavities and micro cracks on the polished surface, which are the intrinsic defects generated in the deposition process of CVD diamond film. The tensile stress of the film reduced through polishing as the release of the deformation energy stored in the film.

Abstract: This study compares the effectiveness of different polishing slurries for Double Sided Polishing process of Silicon wafer in the polished surface roughness and stock removal rate, discusses the mechanism of Double Sided Polishing for silicon wafer with different type slurries, also the influence of the pH value, temperature and concentration of the slurries are discussed in this paper. Furthermore, by the optimization of the process parameters, the ultra-smooth of polished surface of silicon wafer has been got with higher efficient.

Abstract: The new thought for designing the multi-phase and multi-scale nanocomposites was proposed to improve the comprehensive mechanical properties. Multi-phase and multi-scale particles are added to the matrix, and one of the additives is nano-scale particle, thus the comprehensive mechanical properties can be improved by the synergic effects of micro-scale toughening, nano-scale strengthening and mutual benefit between multi-phases. The ideal microstructure of multi-phase and multi-scale nanocomposites was designed. With this microstructure, the trans/intergranular fracture modes can be formed, which will consume more fracture energy during the crack propagation, therefore, both the flexural strength and fracture toughness can be improved. An advanced ceramic tool material has been fabricated based on this new thought.

Abstract: This paper researches on the theory of the crown modification of cylinder-roller bearing raceway using electrochemical abrasive belt grinding (ECABG) technology, and establishes relevant experimental device. The range of processing parameters with a better surface roughness can be obtained through experiments. On this basis, a mathematics model of distribution of material removal of electrochemical machining bearing is set up. Considering the controllability of processing parameters and demand of the surface quality, the processing parameters such as interelectrode voltage, electrolyte, interelectrode gap and cathode geometry are invariable in the experiment, and processing time is changed to control the crown value. The experimental results show that ECABG can enhance the surface quality of raceway to a great degree, and obtain the ideal forming crown at the same time under the optimum technological parameters. This paper developed a new method for the crown processing and finishing of bearing raceway.