Materials Science Forum Vols. 532-533

Abstract: The within-wafer non-uniformity (WIWNU) of material removal rate in chemical mechanical polishing (CMP) is important for IC manufacture. The non-uniform distributions of polishing pressure and the relative speed between the wafer and the polishing pad are main factors affecting the WIWNU. In this paper，based on the contact mechanics and the elastic plate theory, a compensate pressure computing model is presented, in which the effects of kinematic parameters are taken into acount. By modelling and calculating, the desired compensate back pressure distribution is obtained. In the last section the design of a schematic carrier with multi-zone, in which the compensate back pressure can be applied, is presented. The model and the design can be used for providing theoretical guide to the development of CMP equipments and selection of the kinematic variables in CMP process.

Abstract: Primary heat dissipation method of IC Chip is still air-cooling at present. This paper presents a new machining method of air-cooled plate fin heat sinks, namely orthogonal planing. The surface of plate fins machined by this method are rough enough to augment its specific surface area; the rough surface can also disturb laminar sub-layer of turbulent thermal boundary layer, thus the thermal resistances of thermal boundary layer are reduced. Therefore, heat dissipation efficiency of heat sink can be enhanced further. The focus of plate fin heat sinks forming by orthogonal planing is how to machine flat chips. A new pattern of chip curl that is called down-curl can be observed when rake angle of tool is rather large and cutting thickness is very thin. As cutting thickness increases, down-curl chips become flat and then up-curling. There is a transition area that chips are not curled between down- and up-curl. The conditions that chips are not curled are obtained through investigating influences of rake angle and cutting thickness on chip curl, and flat plate fins with rough surface are produced.

Abstract: Aiming to study the surface integrity of an ultra-high strength alloy in high speed milling process, 2K factorial design experiments were conducted to explore the effects of cutting parameters, such as cutting velocity, feed rate and depth of cut, on microstructure, microhardness and residual stress in the sub-surface layer. The following conclusions could be drawn from this paper within the range of cutting conditions: The cutting parameters could significantly influence the microstructure and microhardness in the surface and sub-surface layers, and the original fine martensite of the surface and sub-surface layer might be transformed into the over-tempered martensite, under-tempered martensite, secondary troostite, and tempered sorbite; Compressive residual stress distributions with different maximum stress values in the sub-surface layer of machined surfaces could emerge in high speed cutting process; the properly arranged cutting condition could achieve ideal surface characteristics and surface integrity.

Abstract: An advanced ceramic cutting tool material Al2O3/TiC/TiN is developed by means of adding micro-scale TiC particle and nano-scale TiN particle dispersion. With an optimal dispersing and fabricating technology, this multi-scale and multi-phase nanocomposite may get both higher flexural strength and fracture toughness, especially the fracture toughness may reach to 7.8 MPa·m1/2. The micro-scale TiC particle will form the framework microstructure with other particle and the particles will inlay each other. That is why the flexural strength of Al2O3/TiC composite is improved. Another phase such as nano-scale TiN may lead to fining the grains further more, and promote the sintering to get higher density. The uniform and densified microstructure is obtained, the coexisting transgranular and intergranular fracture mode induced by micro-scale TiC and nano-scale TiN can result in remarkable strengthening and toughening effect.

Abstract: Nanocrystalline diamond films (NDFs) were deposited on mirror-polished silicon (100) substrates using a graphite-grid assisted hot filament chemical vapor deposition (HFCVD) technique. The evidence of nanocrystallinity, smoothness and purity was obtained by characterizing the sample with various advanced analyses. A graphite-grid was used as the DC electrode, which was pre-coated by diamond films and could emit electron when a negative bias was applied to the under electrode. The results show that the film consists of nanocrystalline diamond grains with sizes of about 7-15nm. The Raman spectroscopy, XRD pattern, HR-TEM image and SAED pattern of the films indicate the presence of nanocrystalline diamond. Surface roughness is measured as Ra<20nm by the profilometry scans. A large quantity of electrons emission from the graphite-grid and positive ions bombardment to the graphite-grid results in an enormous enhancement of the generation of diamond nuclei. Density of a diamond nuclei as high as 1010~1011/cm2 can be attained with this method. NDFs can be deposited on mirror-polished Si substrate surfaces without damaging surface pretreatment for nucleation enhancement. These ultra-smooth films will display excellent performances, which make them the best candidates for semiconductor and MEMS applications.

Abstract: A modified coating layer had been deposited on the surface of the workpiece with the electrode made of special materials by normal Electrical Discharge Machining (EDM) method in the recent years, and the surface performance had been improved. But, it also has been found that the deposited materials from the electrode can’t be melted fully on the workpiece and the compact coating can’t be formed because of the quencher and quickly heated effect with normal EDM pulse generator in the experiments. And there are other problems existing such as residual stress, crack and so on. In order to solve the above problems, a kind of special Electrical Discharge Coating (EDC) pulse generator is designed in this paper. The hard coating with less crack and higher coating efficiency can be expected with this special generator.

Abstract: Effects of the scratching feed on machined surface and scratching forces are studied by using AFM-based nanomachining process scratching along the long axis of the cantilever. Results show: A deeper structure and rougher surface can be obtained at a smaller feed. An increase in the feed results in increases in scratching forces and the resultant force and a decrease in the normal force. Finally, all forces reach to a saturation value. The ratio of the cutting force to the thrust force in the plane perpendicular to the cutting edge can reveal effects of ploughing and cutting between the tip and the sample in the nanomachining process. Correspondingly, different states (cutting or ploughing) play a key role in formation of the machined surface at different feeds.

Abstract: Once expandable polystyrene (EPS) foam has been used out, its high volume-to-weight ratio becomes a serious problem, and it is now prototypical high-bulk/non-burnable landfill problem. This is one of main obstacles for EPS foam to be recycled. This paper is concerned with volume reduction method for wasted EPS foam. The analysis is focused on the description of importance of volume reducing method for EPS foam. Wasted EPS foam has not been recycled effectively since its volume to weight ratio is extremely high. The large volume of EPS has prevented from its proper recycling because of high cost of transportation to recycling plant. In this reason, successful recycling of wasted EPS foam results directly from successful volume reduction of wasted EPS foam in proper manner. This paper deals with various existing methods for volume reduction of wasted EPS foam. Six existing processes of volume reduction for wasted EPS has been analyzed qualitatively and compared each other in terms of expected polystyrene (PS) characteristics after volume reduction, cost effectiveness of each process, possible effects on environment caused by the volume reduction process, and applicability to possibly recycled products. The methods analyzed in this paper include thermal, solvent, far infrared, pulverization, and mechanical compaction. Analysis was concentrated to compare each process mostly in qualitative manner among existing processes.

Abstract: For the complexity of weld, the automatic inspecting for the tubular joints which are in working is difficult. Therefore the scanner which has three degrees of freedom for inspecting of large-diameter tubular joints was studied and manufactured based on the scanning principle of ultrasonic phased array. The following of probe to weld is realized by the simultaneous motion of two degrees of freedom and the pose between probe and weld is adjusted by the other degree of freedom. The control strategy of the scanner was provided. Experiments were made with scanner on reference blocks, the results indicate that the automatic ultrasonic phased array inspection is more excellent than the conventional ultrasonic inspection in reliability and repetition.

Abstract: With the rapid development of high-speed machining technology, more and more machining centers have been equipped with the HSK toolholders. In this paper, the performances of the HSK spindle/toolholder interface, such as the axial movement, the radial deflection and the contact stress distribution, were simulated by means of the finite element method and compared with the traditional BT interface. From the simulated results, it was pointed out that the performances of the HSK interface were obviously superior to that of the BT interface, and the HSK interface was much more suitable for high-speed machining.