Polishing Load Research Articles

Novel full-scale model verified by atomic surface and developed composite microfiber and slurry polishing system

Polishing mechanisms between fibers of a polishing pad and slurry are elusive, rising a challenge to develop high-performance composite polishing system. To solve this challenge, a novel full-scale model is proposed from mm to nm, consisting of macro, meso, micro and nanoscale. The model is verified by atomic surface and developed composite microfiber and slurry polishing system. Prior to chemical mechanical polishing, fused silica was polished by ceria slurry. A novel polishing pad was prepared using microfibers with a diameter of 2.5 μm, and a novel green slurry contained silica abrasives, hydrogen peroxide, sodium carbonate, sorbitol and xanthan gum. After CMP, an atomic surface with Ra of 0.108 nm was achieved, and the thickness of damaged layer is 1.95 nm. In terms of the macroscale model suggested, the maximum stress on the microfiber pad decreased 417.7 %, and the direct contact area increased 41.23 % compared with those of a commercial nonwoven pad. The peak stress exceeded 1 MPa on the commercial pad, while it reduced to about one fourth on the developed microfiber pad, according to the mesoscale fiber-slurry model proposed. Reactive force field molecular dynamics simulations, i.e. nanoscale model, reveal that a slurry layer existing at interface effectively impedes direct contact between abrasives and fused silica. With increasing the polishing load, material removal mode transformed from an atom to atomic chains. The constructed full-scale model and developed composite polishing system provide new insights to analyze, design and manufacture high-performance polishing pads, slurry and system.

Proposal of Magnetic-Force-Assisted Polishing Method

To reduce the size of the polisher, especially the polishing head, a novel method for applying the polishing load using magnetic force is proposed. As the fabrication of next-generation power device substrates advances, such as diamond, ultra-precise planarization via chemical mechanical polishing (CMP) becomes crucial for transforming these substrates into functional devices. Achieving CMP necessitates the application of an optimal polishing load to the substrate. Deadweight and air pressure methods are the traditional mechanisms for delivering this load. However, they tend to increase the size and complexity of the polishing head mechanism, hindering its miniaturization. This study proposes leveraging the magnetic force for the application of polishing load. Such an approach not only promises the miniaturization of the polishing head but also paves the way for smaller polishers. We constructed a prototype polisher with a straightforward mechanism and conducted several tests. The removal rate measurements from these tests, when compared with those of the traditional deadweight method in prior research, validated our approach. Additionally, by adjusting the magnet spacing (which adjusts magnetic force) and the rotational speed, we found that the removal rate adheres to Preston’s law even when employing the magnetic force for polishing.

Influences of process parameters on chemical mechanical polishing effect of ZnGeP2 crystal

To obtain the ultra-smooth surface of ZnGeP2 crystal (ZGP), the workpiece-abrasive-polishing pad contact model during polishing was established to calculate the load Fw and the cutting depth hw of a single abrasive. The influences of polishing methods, abrasive hardness, abrasive size, polishing pressure, polishing time and other factors on the polishing effect were studied, and the mechanism underpinning the formation of surface morphology after polishing was revealed, and the mathematical model between material removal rate (MRR) and surface roughness (Ra) was established. The results show that the critical cutting depth hc of ZnGeP2 crystal is 95.21 nm, when the polishing load is 5 N, the material removal under mechanical polishing and chemical mechanical polishing entails plastic removal. Compared with mechanical polishing, the MRR of chemical mechanical polishing is increased by 23.4% and Ra is decreased by 26.5%. The increases of abrasive hardness, abrasive size and polishing load will increase the cutting depth hw of the abrasive, resulting in the increases of MRR and Ra, but the influence forms of various factors are different. After optimizing the process parameters, the minimum Ra of ZnGeP2 crystal is 0.76 nm. MRR and Ra will decrease significantly with the increase of polishing time, and there is a significant correlation between them.

Abrasive polishing load effect on surface roughness and material removal rate of Al2O3, ZTA and SiC

The surface quality determines the performance of ceramic tribological components, e.g., bearings and seals. Surface conditioning processes, like polishing, are generally responsible for the largest portion of the manufacturing costs of these components. Therefore, process parameters, such as polishing load, should be optimized for economic reasons. Sintered alumina (Al2O3), zirconia-toughened alumina (ZTA) and silicon carbide (SiC) samples were polished in a sequential two-step process using a water-based diamond abrasive slurry with particle sizes of 3 μm (P1) and 1 μm (P2) on woven and nap cloths, respectively. The effect of material and polishing load (40, 50 and 60 N) on 2D roughness parameters (Ra, RSm, Rz and Rsk) and material removal rate (MRR) were evaluated by a MANCOVA statistically designed experiment. Polishing steps reduced Ra and Rz in succession, with the greatest absolute reduction occurring at P1. Load and material affected only MRR and RSm, when controlled by the effect of initial roughness parameters of surfaces. The low surface porosity fraction combined with very low Ra of surface topography plateaus, especially after P2, resulted in much higher RSm values for SiC. Atomic force microscopy (AFM) images of polished surfaces revealed that, on a finer scale, material removal mechanisms were ductile. MRR for SiC was the highest and proportional to polishing load, while the load did not affect it for the oxide ceramics. The synergy between the mechanical action of abrasives and tribochemistry between SiC and water explains its higher MRR and better surface finish, while Al2O3 and ZTA relied mainly on the ductile mechanisms to improve their surface quality.

Evaluation of the polishing resistance characteristics of fine and coarse aggregate for asphalt pavement using Wehner/Schulze test

Traffic safety is influenced strongly by the skid resistance of pavements. Moreover, the long-term skid resistance of pavements depends mainly on the polishing resistance of the specific aggregate present on the surface. The polishing resistance is a measure which describes the roughness of aggregate after a polishing load has been induced by traffic loads. Specifications for the polishing resistance of aggregate are given only for coarse aggregate. However, given the various mixture types it is questionable if the fraction of fine aggregate (up to 55 M.-%) ought to be neglected, particularly since the polishing resistance of fine aggregate is higher than that of coarse aggregate. This paper aims to quantify the polishing resistance of various aggregate size fractions with particular focus on the properties of fine aggregate, and to demonstrate the suitability of the Wehner/Schulze test (W/S) in this regard. The results show that the initial skid resistance and the polishing resistance of fine aggregate are generally greater than that of coarse aggregate. It is notable that the initial skid resistance decrease is far more pronounced for fine aggregate. The polishing resistance does not exhibit a uniform development across all aggregate sizes. It is to be expected that fine aggregate may play a significant role for the skid resistance of asphalt pavements; however only coarse aggregate is considered in the design process. Further research is needed to precisely determine the effect of fine aggregate to allow for more economically feasible pavement designs.

Figure correction of a metallic ellipsoidal neutron focusing mirror.

An increasing number of neutron focusing mirrors is being adopted in neutron scattering experiments in order to provide high fluxes at sample positions, reduce measurement time, and/or increase statistical reliability. To realize a small focusing spot and high beam intensity, mirrors with both high form accuracy and low surface roughness are required. To achieve this, we propose a new figure correction technique to fabricate a two-dimensional neutron focusing mirror made with electroless nickel-phosphorus (NiP) by effectively combining ultraprecision shaper cutting and fine polishing. An arc envelope shaper cutting method is introduced to generate high form accuracy, while a fine polishing method, in which the material is removed effectively without losing profile accuracy, is developed to reduce the surface roughness of the mirror. High form accuracy in the minor-axis and the major-axis is obtained through tool profile error compensation and corrective polishing, respectively, and low surface roughness is acquired under a low polishing load. As a result, an ellipsoidal neutron focusing mirror is successfully fabricated with high form accuracy of 0.5 μm peak-to-valley and low surface roughness of 0.2 nm root-mean-square.

Failure Mechanisms of CVD Diamond Wafers and Thin Films During Polishing

This article investigates the failure mechanisms of CVD diamond wafers and thin films during a fast dynamic friction polishing process. To explore the evolution of temperature and stress fields, a comprehensive finite element analysis was systematically carried out, with the aid of experimental examination. It was found that the discontinuity and sharp change of the stresses across the film-substrate interface causes debonding failure of a CVD diamond thin film specimen. In the case of a CVD diamond wafer, however, the high surface tensile stress and bulk bending is responsible for the cracking. It was concluded that specimen cracking is sensitive to the polishing pressure, and that the polishing window for the CVD thin films is smaller. Polishing time is a critical factor, because a longer time corresponds to a higher thermal stress. This article points out that using the combination of a smaller polishing load and a greater sliding speed is a good option in selecting polishing parameters. To minimize cracking, a stepwise polishing process can be used. With the proper parameters obtained in this study, very smooth, high-quality surfaces of CVD diamond wafers and thin films can be produced in a short polishing duration of minutes.

S1360102 板ばねを利用した研磨による月面反射鏡の平滑加工技術の開発

A high precision measurement system of the distance between the moon and earth is under development by the National astronomical observatory of Japan, in which the round-trip time of laser from the earth to the moon is measured to calculate the distance. In the system, a new lunar laser reflector (LLR) placed on the moon is necessary to measure the round-trip time, but has not yet been realized. In this study, we proposed a new polishing method using a plate spring suitable for polishing the LLR to realize it. To evaluate our proposed method, we polished single crystal Si wafers as workpieces, and examined surface roughness and machined shapes of the polished areas. As a result, surface roughness after the polishing was better than that before polishing. This proves that our proposed method using the plate spring enables the smoothing of surfaces. However, the machined areas were not shaped to flat, but to be curved. The reason for this is possibly due to the non-uniformity of the polishing load. Thus, the flatness of the machined areas should be improved in future study.

Influence of freeze–thaw on the polishing resistance of coarse aggregates on road surface

The aggregates used for surface layers are of central importance for the skid resistance of a road as they are subjected to a combined load due to traffic and weather conditions. In this paper, different aggregates are selected and two plate specimens are produced using each aggregate. One of the test plates is subjected to solely polishing load and the other one was treated with a combined load of polishing and freeze–thaw cycles. By comparing the texture changes and the skid resistance development, a statement is derived on the impact of a freeze–thaw effect for the short-term and long-term development of skid resistance.

Micro-Aspheric Mold Polishing Utilizing Magnetostrictive Vibration-Assisted Polishing Machine

Micro-aspheric lenses molded by micro-aspheric ceramic molds are increasing in the optical systems such as digital cameras and blu-ray players. To finish the molds with high accuracy and low surface roughness, in this paper, the micro-aspheric mold made of Electroless nickel plating are polished by using the newly developed 5-axis magnetostrictive vibration-assisted polishing machine. The magnetostrictive vibrating polisher generates a lateral vibration at 9.2 kHz with amplitude of 30 μm. The polishing pressure is controlled by a balance adjustment mechanism and the polishing load is controllable within a range of 2 mN ~ 20 mN with a resolution of 2 mN. The motion resolution of the X-Y-Z table is 0.1 μm in each direction. The C-axis rotary table is mounted on a B-axis tilting table and the workpiece is mounted on the C-axis rotary table with a vacuum chuck. According to the polishing experiments, the form accuracy was improved to 200 nm P-V and the surface roughness was reduced to 10 nm Rz (1 nm Ra).

Modeling the effects of particle deformation in chemical mechanical polishing

In a chemical mechanical polishing (CMP) process, an active abrasive particle participating in the wear process will contact the pad and the wafer at the same time. The applied polishing load causes the deformation of the pad in the contact interface of the particle and the pad, and the deformation of the wafer in the contact interface of the particle and the wafer. Besides, this force causes the deformation of the abrasive particle. Based on the elastic–plastic micro-contact mechanics and abrasive wear theory, a novel model for material removal rate (MRR) with consideration of the abrasive particle deformation is presented in this paper. The deformation of the abrasive particle, affecting the indentation depth of the particle into the wafer, is quantitatively incorporated into the model. The results and analyses show that the present model is in good agreement with the experimental data.

Computational Solid Mechanics Modeling of Asperity Deformation and Pad-Wafer Contact in CMP

ABSTRACTAsperity-scale pad deformation and dynamic pad-wafer contact area are crucial to the fundamental understanding of material removal and defect formation mechanisms in CMP. Pad asperity stress and strain are also central to characterizing pad wear rate during polishing and cut rate during conditioning. While it is very difficult to isolate and measure stress and strain in individual asperities, finite element modeling may be used in conjunction with experimental surface characterization to predict asperity-scale deformation and pad-wafer contact. Asperity sub-domains up to 1270 microns across are reproduced from three-dimensional point cloud data on porous polyurethane CMP pads obtained by confocal microscopy, meshed to high resolution, and analyzed using ABAQUS finite element software. Physical properties are derived from dynamic mechanical experiments. Pad stacks are simulated both with and without sub-pads. Results show that while a sub-pad increases pad-wafer contact area overall, it limits the local spreading of individual contact regions as polishing load increases. This finding identifies a direct mechanical origin of the trade-off in pad design between wafer-scale and die-scale planarity. As expected, the real contact area between a pad and wafer is much smaller than the cross-sectional or “bearing” area, but the difference is notably greater when a sub-pad is present. Values of asperity stress and strain under typical CMP polishing pressures reveal that plastic deformation takes place both on and beneath the contacting surface. Hence upon release of the polishing load the asperities do not fully rebound to their pre-compressed shapes. Each pass under the wafer thus reshapes the pad asperities such that a slightly different texture is presented upon the next pass. These deformation mechanics clarify the impact of top pad and sub-pad properties on real contact area, allowing better optimization of CMP pad performance.

An evaluation of the effects of handpiece speed, abrasive characteristics, and polishing load on the flexural strength of polished ceramics

Many studies on the strengthening effects of grinding and polishing, as well as heat treatment on ceramics, are not well standardized or use commercially available industrial polishing systems. The reported effectiveness of these strengthening mechanisms on ceramics may not be applicable to clinical dentistry. The purpose of this study was to evaluate the effects of controlled polishing on the flexural strength of dental ceramics by using a custom-made machine that applied standardized loads and speeds that coincided with the mean loads and speeds used by experienced prosthodontists. A total of 140 aluminous dental ceramic bar-shaped specimens (Vitadur Alpha Enamel) measuring 1.5 x 2.0 x 25 mm were fabricated and divided into 12 groups (for most groups, n=10). Specimens were untreated, polished with different polishing systems, polished at different speeds, ground and autoglazed, polished and autoglazed, autoglazed and polished, polished with loose (paste) and bonded abrasives, or overglazed. Simulated clinical polishing was performed on the ceramic specimens by using a customized polishing apparatus that allowed independent control over the relevant polishing parameters (abrasive hardness, applied load, linear speed, rotational velocity, and wheel stiffness). Flexural strength (MPa) was measured with a 4-point bending test, and subjective surface roughness was assessed with scanning electron microscopy. Autoglazing was performed at various stages of the polishing sequence to determine the effects of polishing on surface stresses. Mean values, standard deviations, independent-sample t tests, 1-way and 2-way analyses of variance, Dunnett t tests and Kruskal-Wallis tests were applied to the data (alpha=.05). Under a clinical load of 0.6 N for a coarse polishing wheel, 1.0 N for a medium polishing wheel, and 1.3 N for a fine polishing wheel, a linear speed of 499 mm/min, and a rotational velocity of 10,000 rpm, the use of clinical polishing instruments did not affect the flexural strength of the aluminous ceramics studied (P=.274). At higher rotational velocity (20,000 rpm), specimens polished with the diamond polishing system produced statistically weaker specimens compared with those that had been polished at 10,000 rpm (P=.019). Autoglazing treatment of the diamond-polished specimens did not reverse the strength degradation (P=.125). Conversely, diamond polishing of the autoglazed specimens resulted in significant flexural strength reduction (P=.029). Fine-diamond-bonded abrasive significantly reduced flexural strength (P=.025). Simulated clinical polishing at 10,000 rpm did not appear to substantially strengthen or weaken the ceramic specimens. Polishing at 20,000 rpm reduced flexural strength of the ceramic bars.

Polishing of polycrystalline diamond by the technique of dynamic friction, part 1: Prediction of the interface temperature rise

This paper investigates the interface temperature rise in polishing a polycrystalline diamond (PCD) surface. First, the Greenwood–Williamson's statistical asperity model is applied to characterise the surface roughness of a PCD specimen. The result is then used to estimate the contact area and total number of contact asperities under an applied polishing load. The heat generated is taken as the product of the friction force and the relative sliding velocity between the PCD asperities and the metal disk surface. The Jaeger's moving heat source analysis is then applied to determine the fractions of heat flux flowing into the PCD asperities and their counterpart in contact sliding and to give rise to the average temperature rise. A comparison with the observations made in the authors' experiments and those reported in the literature showed that the model predicts very well the temperature rise at the polishing interface.

The polishing process of advanced ceramic balls using a novel eccentric lapping machine

The finishing process of advanced ceramic balls can be divided into two steps. The first step is lapping in which most of the stock from the ball is removed at a higher material removal rate. The second step is polishing in which the required ball surface roughness, roundness, and dimensional and geometric accuracy are achieved. In polishing, the abrasive particle size is 1 μm, and the load and speed are lower than lapping. A novel eccentric lapping machine is used for polishing hot isostatically pressed (HIPed) silicon nitride balls. In the initial polishing stage, the polishing load is demonstrated as being most influential in the reduction of surface roughness value Ra. However, in the later polishing stages, the erosive process played a major role in the further reduction of Ra, although the high roughness peaks cannot be removed by erosive process alone. Experimental results also show that, in order to achieve desired surface roughness value, the initial surface quality of the upper plate should be reasonably high, and deep scratches on the ball surface from previous lapping processes should be avoided. The best polishing results achieved were surface roughness values of Ra of 0.003 μm and r.m.s. ( Rq) of 0.004 μm, ball roundness of 0.08–0.09 μm. This proves that the novel eccentric lapping machine is also suitable for polishing advanced ceramic balls.

Fluid pressure and its effects on chemical mechanical polishing

The experimental results of interfacial fluid pressure and friction measurements during polishing are presented, as well as their dependence on some major process variables. Under simulated conditions, a sub-ambient fluid pressure was observed, and its magnitude was of the same order of magnitude as the applied polishing load. Since this fluid pressure is non-uniformly distributed, the contact stress, obtained by combining the effects of both applied load and the fluid pressure, is not uniform across the wafer and will result in non-uniform material removal. The mechanism of the presence of the fluid pressure was investigated, and an analytical model was developed to predict the magnitude and distribution of this fluid pressure. The effects of the sub-ambient fluid pressure on material removal rate and profile were tested with thermally grown silicon dioxide on 100 mm diameter, p-type (1 0 0), single-crystal silicon wafers. The polishing experiments show the effect of sub-ambient fluid pressure on polishing rate and profile.

Polishing Mechanism And Its Effect On The Mechanical Properties Of Ceramic Restorations - A Review Of The Literature

Polishing of dental ceramics has become an increasingly important procedure in restorative dentistry as allceramic restorations, which require post-cementation occlusal adjustment, are gaining in popularity. There are numerous studies in both dental and ceramic literature on polishing of dental ceramics and the effects of polishing on their mechanical properties. However, lack of standardization in polishing parameters, precludes comparison among these studies. A clear understanding is lacking of the relative roles and interdependence of handpiece speed, abrasive characteristic, and polishing load. This paper will discuss the mechanism of polishing and review the literature on polishing and its effect on the mechanical properties of ceramic restorations.

アレーベア光ファイバーの一括端面加工

A precise process for machining arrayed optical fiber ends to have tapered corners and slightly convex planes for use as the bare optical fiber connectors have been developed. The taper shapes are determined by the length L of the fiber from holder to the fiber ends, the height h of the holder, and number of revolutions. The underlying principle is that the machining amount is proportional to the product of the load and the work traveling length. The curvature radius (8 to 18 mm) of the slightly convex fiber end plane can be controlled by adjusting the polishing load. The polished plane with the silica abrasive lapping film has high optical return loss (55 to 60 dB).

Computational modelling of a precision optical lens polishing process on small radius spherical surfaces

A thorough understanding of the mechanics of contact and friction mechanisms is of great practical importance to the process of precision optical lens polishing. The present work is aimed at modelling the polishing process for spherical optical lenses with small radii (r=(5.50–8.85)×10 −3 cm) . A finite element technique (ABAQUS/Standard) was employed to perform the analysis. The results include information about the contact status during the polishing process, the polishing load distribution on the contact surface and the variation of the spatial polishing trace. The problem of the missing polishing zone on the workpiece is also discussed.

Material removal in the optical polishing of hydrophilic polymer materials

The optical polishing of hydrophilic polymer materials is a complex process that requires a comprehensive setting of various operating parameters. Based on a series of experimental investigations and dimensional analysis, this paper presents a simple empirical equation to evaluate material removal in the polishing of optical spherical surfaces of hydrophilic polymer materials. It is shown that the polishing load applied governs the material removal, the relative sliding velocity and the sliding distance between the workpiece and polishing tool surfaces. The equation also offers a good reference for the setting of the polishing variables.