Double-sided Lapping Research Articles

Double-sided lapping uniformity of LiTaO<sub>3</sub> based on three-dimensional trajectory of particles

Double-sided lapping uniformity of LiTaO<sub>3</sub> based on three-dimensional trajectory of particles

Effect of pad surface morphology on the surface shape of the lapped workpiece

Double-sided lapping is currently the mainstream manufacturing method for obtaining plane-parallel optical workpieces with high surface shape accuracy, and the fixed abrasive lapping pad is the main machining tool. However, the effect of pad surface morphology on the workpiece surface shape has rarely been studied, and its formation mechanism has not yet been revealed. In this paper, based on probabilistic statistics and contact mechanics, an analytical model that takes into account the pad surface morphology for predicting the workpiece surface shape evolution is developed. Notably, this model considers the cross-scale relationship between the formation of lapped surface shape and the scratching process of a single abrasive grain in material removal for the first time. Furthermore, the real-time dynamical contact relationship between the workpieces and the measured actual pad surface morphology is also considered. The surface shape and peak-to-valley value of the workpiece under different parameters were simulated and analyzed, and the influence mechanism of the local profile and macro shape of the lapping pad on the lapped workpiece surface shape are clarified. Moreover, the double-sided lapping trial experiments were performed to validate the theoretical model, and the experimental results demonstrated good agreement with the simulation results. The maximum error of the surface shape evolution prediction model is less than 14.6 %. This result verifies the correctness and validity of the established model. This work not only provides new ideas for controlling the workpiece surface but also forms the theoretical basis for understanding the double-sided lapping process.

Why Parallelism of Workpieces Becomes Convergent During Double-Sided Lapping?

AbstractDouble-sided lapping (DSL) is always employed as a precision process for machining flat workpieces, such as optical windows, wafers, and brake pads taking advantage of its high efficiency and parallelism. However, the mechanism of parallelism error reduced by the DSL process was rarely investigated. Furthermore, the relationship between parallelism and flatness was not clearly illustrated. To explain why the parallelism of workpieces becomes convergent by the DSL, a theoretical model has been developed in this paper by calculating the parallelism evolution with the consideration of various contact situations between workpieces and lapping plates for the first time. Moreover, five workpieces, including a slanted and four parallel ones, are applied to develop the parallelism evolution guaranteeing the model close to the actual process, and the mechanism of the parallelism error reduced by the DSL process is elucidated. The calculation result revealed that the parallelism was improved from 100.0 µm to 25.6 µm according to the proposed model. The experimental results showed that the parallelism error reduced from 108.6 µm to 28.2 µm, which was consistent with the calculation results.

Stress-Induced Deformation of Thin Copper Substrate in Double-Sided Lapping

Double-sided lapping is an precision machining method capable of obtaining high-precision surface. However, during the lapping process of thin pure copper substrate, the workpiece will be warped due to the influence of residual stress, including the machining stress and initial residual stress, which will deteriorate the flatness of the workpiece and ultimately affect the performance of components. In this study, finite element method (FEM) was adopted to study the effect of residual stress-related on the deformation of pure copper substrate during double-sided lapping. Considering the initial residual stress of the workpiece, the stress caused by the lapping and their distribution characteristics, a prediction model was proposed for simulating workpiece machining deformation in lapping process by measuring the material removal rate of the upper and lower surfaces of the workpiece under the corresponding parameters. The results showed that the primary cause of the warping deformation of the workpiece in the double-sided lapping is the redistribution of initial residual stress caused by uneven material removal on the both surfaces. The finite element simulation results were in good agreement with the experimental results.

Preface

The 2022 International Conference on Advanced Mechanical, Electronic and Electrical Engineering (ICAMEE 2022), an online conference, was successfully held on August 26-28, 2022 in Qingdao, China. ICAMEE 2022 provided experts, scholars, and engineering technicians in the fields of electrical engineering and mechatronics with shared scientific research results and cutting-edge technology, promoting cooperation in the industrialization of academic achievements.We were extremely honored to invite both Prof. Ziad Moumni from ENSTA Paris Tech, France and Prof. Shahid-Hussain from Jiangsu University, China to serve as our Conference General Chairs. There were 160 individuals and enterprises attending the conference. Divided into three parts, the conference agenda covered keynote speeches, oral presentations, and online Q&A discussion. Firstly, keynote speakers were each allocated 30-45 minutes to hold their speeches. Then in the oral presentations, the excellent papers we had selected were presented by their authors by turns.During the conference, four sophisticated professors were invited to address keynote speeches. Among them, Prof. Jiang Guo from Dalian University of Technology, China delivered a speech on the topic: Investigation on High Precision Double-Sided Lapping Process. The controlment of surface shape in double-sided lapping process was rarely investigated in previous researches. Therefore, this speech presented a double-sided lapping process with fixed abrasives, and analyzed the influence of residual stress on workpiece deformation. Additionally, Assoc. Prof. Anwar Ali from Zhejiang Sci-Tech University, China gave a report on the Attitude Control of a Small Spacecraft using Reconfigurable Embedded Magnetorquers. He showed that the nanosatellite market is rapidly growing for scientific and commercial applications, enabling many universities and small and medium-sized enterprises (SMEs) to develop their own satellites. To deal with the problem of small satellites’ space and weight constraints for housing a large number of required subsystems, attitude control system was proposed in this research and orientated the satellite in space to rotate solar panels towards Sun and antennas towards ground station. The wonderful and dramatic speeches of each keynote speaker had triggered heated discussion. Moreover, every participant praised this conference for disseminating useful and insightful knowledge.After months of well preparation and hard work, the proceedings of ICAMEE 2022 covering a bunch of papers are smoothly published. These papers feature but are not limited to the following areas: Mechatronics Control, 3D Printing Technologies, Electrical materials, Signal processing, etc. All the papers have been checked through rigorous review and processes to meet the requirements of publication.On behalf of the conference organizing committee, we would like to express our heartfelt appreciation to all the keynote speakers, peer reviewers, and all the participants. In particular, we would like to acknowledge the Journal of Physics: Conference Series, for the endeavor of all its colleagues in publishing this paper volume. We firmly believe that all the attendees have had fruitful discussions and gained valuable knowledge, and will enjoy the opportunity for future collaborations.Committee of ICAMEE 2022List of Committee member is available in this Pdf.

Formation mechanism of concave and convex surface shapes in double-sided lapping

Double-sided lapping process is a key technology for obtaining high efficiency and flatness in fabricating plane-parallel workpiece surfaces, such as wafers, optical windows, seal rings, etc. However, the formation of the concave and convex surface shapes of workpieces was rarely investigated in the previous research, and the mechanism was unknown. This paper establishes a new kinematic model to clarify the formation mechanism of concave and convex surface shapes, in which the workpiece eccentricity and rotation in the planetary wheel are considered for the first time. The measurement and control method of workpiece rotational speed in the planetary wheel is proposed. The formation of the concave and convex surface shapes is validated experimentally by adjusting the rotational speed of the workpiece, and the results show a good consistency with the calculation results. A flatness error convergency method is proposed based on the surface shape formation mechanism, and flatness superior to 5 µm is achieved on Φ200 × 2 mm thin copper substrates.

Study on factors affecting wafer actions during double-sided lapping

Study on factors affecting wafer actions during double-sided lapping

Edge roll-off suppression method in double-sided lapping with fixed abrasives.

Edge roll-off affects the performance of key parts in precision optics processing. Currently, the evolution mechanism of edge roll-off is not understood clearly, and the existing suppression methods for edge roll-off are not qualified in real applications. To address the problem, this paper presents a new edge roll-off suppression method in double-sided lapping with fixed abrasives. The evolution mechanism of edge roll-off in double-sided lapping is analyzed by utilizing the finite element method (FEM). Three key influential factors affecting edge roll-off, including filling materials and the width of the sacrificial and filling loops, are optimized by FEM analysis and verified by experiments. By applying the optimized parameters, the depth and width of the edge roll-off on thin copper substrates are reduced by about 80% and 55%, respectively.

A calculation method for workpiece profile variation during double-sided lapping by considering workpiece elastic deformation

A calculation method for workpiece profile variation during double-sided lapping was developed in this study. In this method, shell element in FEM deformation was used to formulate elastic deformation of workpiece, and spring element was used to formulate the contact between workpiece and platens to calculate distribution of their contact pressure considering workpiece elastic deformation. First, the developed method of the contact pressure distribution was evaluated by comparing with a method using a FEM software and the existing methods, and was confirmed to be quite valuable in terms of applicable process and calculation time. Subsequently, the workpiece profile variation was calculated using the developed method for several workpiece conditions, and it was clarified that the uneven workpiece thickness can be modified by the process, but it is difficult to modify the bow shape when the workpiece is not small. Furthermore, the decrease of the load applied to the workpiece was suggested to modify the bow shape of the workpiece.

A novel measurement method for the torque acting on the upper platen in a three-way double-sided lapping/polishing machine

In double-sided lapping and polishing processes, the friction coefficients between the workpiece and platens or pads are important parameters for understanding or improving the lapping and polishing processes. However, the friction coefficients have not been investigated in detail owing to insufficient measurement methods for the torques acting on the upper and lower platens, which are necessary to evaluate the friction coefficients. Thus, a novel measurement method for the torque acting on the upper platen in a three-way double-sided machine was proposed in this study. In the method, the torque is measured based on the forces acting on the holders supporting the upper platen rotation. The torques were measured with the method in double-sided lapping experiments, and they were confirmed to agree with the theoretical torque variation. Furthermore, the friction coefficient between the workpiece and upper pad identified with the proposed method was also verified by comparing with the friction coefficient measured in the single-sided lapping experiment. In addition, the estimation method of the lower platen torque based on the motor torque was investigated by utilizing the proposed method, and we found the lower platen torque was estimated accurately by taking a sufficient warm-up time or by modeling the torque loss in transmission path. Therefore, accurate measurement of the torques acting on the upper and lower platens, which is an effective tool for understanding or improving the process, was realized.

Thermal and technological aspects of double face grinding of C45 carbon steel

In grinding, the contact zone temperature is a decisive factor influencing the achievable surface quality and the grinding tool wear. In contrast to other grinding processes, only few information regarding double face grinding with planetary kinematics when processing steel is known up to date. Since the successive substitution of industrial double-sided lapping processes by double-sided grinding, it has become necessary to the conducted research in order to provide deeper understanding of the process and factors that influence it. To determine the workpiece temperature during grinding of C45 components, silicon temperature sensors were integrated into the workpiece holders and technological investigations were carried out. The influences and interactions of the mean cutting speed, cooling lubricant flow rate and cutting ability of the grinding wheels on the resulting workpiece temperature were analysed. Subsequently, modelling enabled an empirical estimation of the resulting workpiece temperature for processes in the investigated test area. With regard to the design and optimization of processes for machining plane-parallel workpiece surfaces, this model is a helpful tool for avoiding thermally induced workpiece damage and reduction of tool wear. Furthermore, the method can be used to conduct further examinations on the grinding process and to reduce the amount of cooling lubricant used, to improve life cycle assessment.

Research on factors affecting wear uniformity of the wheels in the double-sided lapping

Uniform wear of lapping wheel helps to improve the surface accuracy of workpiece and increase the lifespan of wheel in double-sided lapping. The relative motion of workpiece has a significant effect on wear uniformity of the lapping wheel. In this paper, the wear uniformity of the wheel was studied from the perspective of the motion trajectory distribution of the workpiece relative to the wheel. We calculated the trajectory distributions on the wheel surface at different rotational speed ratios, workpiece placements and workpiece sizes. In addition, we used the variation coefficients of the standard deviation (VCSD) to evaluate the nonuniformity of the trajectory distribution. On this basis, a series of lapping experiments were executed to confirm the correlation between wear and trajectory distributions. With the rotational speed ratio as an example, the relationship between the wheel lifespan and the wear nonuniformity coefficient (VCSDΔh) is explained. The results show that when the rotational speed ratio was in a certain range, the farther the workpiece was placed from the carrier center and the larger the workpiece size, the better the wear uniformity and the longer the lifespan of the wheel. Thus, reasonable settings for parameters and configurations can prolong the lifespan of the lapping wheel.

The double-side lapping of SiC wafers with semifixed abrasives and resin–combined plates

SiC crystal has been widely used in semiconductor substrates because of its excellent physical, chemical, and photoelectric properties. As a semiconductor substrate, the SiC wafer not only needs good surface quality but also requires surface shape accuracy. In the present study, a novel lapping plate was designed for SiC wafers to improve their surface quality and shape accuracy. In the novel lapping plate, epoxy resin and a soft gel body containing diamond abrasives are combined to form a hard honeycomb structure. The cellular structure is used to support the lapping pressure to reduce the deformation of the lapping plate and improve the surface shape accuracy. The cellular structure is filled with soft gel with diamond abrasives which play the role of semifixed lapping to obtain good surface quality. Two crystalline forms of silicon carbide (4H-SiC and 6H-SiC) were selected to carry out double-sided lapping experiments with the novel lapping plate. The experimental results show that the lapped wafers have good surface quality with low surface roughness, some small scratches, and acceptable cracks. In addition, the surface shape accuracy is improved; the values of bow, warp, and total thickness variation (TTV) are all reduced after lapping. Under the same lapping conditions, the 6H-SiC has a smaller surface roughness than 4H-SiC, and for a specific crystalline form, the surface roughness of the C face is smaller than that of the Si face. The bow and warp of 4H-SiC are smaller, but the TTV is larger. The material removal rate is basically the same for 4H-SiC and 6H-SiC.

Study on the Wear Characteristics of a Lapping Wheel in Double-Sided Lapping Based on the Trajectory Distribution

In the process of double-sided lapping, the surface shape of the lapping wheel changes because of uneven wear, which affects the quality of the workpiece, especially the surface shape accuracy of the workpiece (bow, warp, and total thickness variance). Lapping trajectory is the primary reason for uneven wear on the wheel surface. Therefore, the uniformity of the lapping wheel wear during the double-sided lapping process will be investigated based on the trajectory distribution in this paper. First, the kinematics of double-sided lapping is analyzed, and the lapping trajectory equation is established. Then, the simulation calculation is conducted using MATLAB software to obtain the trajectory distribution characteristics of the wheel surface. The wear uniformity of the wheel surface is analyzed according to the distribution density of the trajectory. The wear model of the lapping wheel surface is established. Finally, double-sided lapping experiments with sapphire slices are carried out. Under varied workpiece material removal thicknesses, the changes of the lapping wheel surface profile are measured, and the wear of the lapping wheel surface along the radial direction is obtained and compared with the calculation results. The calculation results are basically consistent with the experimental results, which proves the correctness of the double-sided lapping wheel surface wear model.

Precision Fabrication of Thin Copper Substrate by Double-sided Lapping and Chemical Mechanical Polishing

Thin copper substrates with high flatness and surface integrity are highly required in precision physical experiments. Normally, fly cutting is used to fabricate the substrates. However, the flatness is difficult to be guaranteed after disassembly due to the clamping and machining stresses which are induced on the substrates. Besides, the surface integrity is hard to be improved because of the severe subsurface deformation and high residual stress. To solve the problem, a new process chain composed by double-sided lapping and chemical mechanical polishing (CMP) is proposed to acquire both high flatness and surface integrity on thin copper substrates. In the new process chain, double-sided lapping is employed to achieve high flatness and uniform distribution of surface residual stress, while double-sided CMP is adopted to obtain the ultra-smooth surface without damage and maintain the flatness. The results show that flatness superior to 4 μm peak-to-valley (PV), and surface roughness less than 3 nm Ra are obtained. Moreover, both surfaces are damage-free with low surface residual stresses.

Development an identification method of friction coefficient between wafer and carrier in double-sided lapping

Behavior of a wafer is one of the most significant concerns in double-sided lapping since it depends on the distribution of material removal rate. Though the wafer behavior is affected by the friction coefficient between the wafer and a carrier, the coefficient has hardly been discussed. In this study, an identification method of the friction coefficient based on variation of wafer rotational speed with wafer position in the carrier during single-sided lapping operation on double-sided lapping machine is developed for accurate estimation of the wafer behavior. The friction coefficient is identified by comparing experimental and theoretical variation of the rotational speed of the wafer. The experiment is carried out under the condition where lubrication condition between the wafer and the carrier is similar to that in double-sided lapping, and the variation is measured by image processing of the wafer behavior. The theoretical variation is calculated based on the equilibrium of force and moment applied to the wafer. It is confirmed that the theoretical rotational speed of the wafer under a friction coefficient condition agrees well with the measured one in terms of not only the highest and the lowest speed but also the variation with the wafer position in the carrier. Thus, it is assumed that the practical coefficient is identified by utilizing this method. In addition, the behavior of the wafer in double-sided lapping is calculated using the identified friction coefficient, and it is suggested that precise consideration of the contact status between the wafer and the carrier, i.e., non-slip, slip, and non-contact is essential for practical estimation.

両面研磨におけるウェハ－キャリア間の摩擦係数の調査 ウェハ－キャリア間の垂直抗力が及ぼす影響の評価

両面研磨におけるウェハ－キャリア間の摩擦係数の調査 ウェハ－キャリア間の垂直抗力が及ぼす影響の評価

Experimental research on the changing process of sapphire substrate surface shape and surface roughness in double-sided lapping

Experimental research on the changing process of sapphire substrate surface shape and surface roughness in double-sided lapping

両面研磨におけるウェハ―キャリア間の摩擦係数推定手法の開発

両面研磨におけるウェハ―キャリア間の摩擦係数推定手法の開発

Analysis of the kinematic model for cylindrical parts in double-sided lapping process

The method of machining cylindrical parts with double-sided lapping through a planet mechanism is discussed in this paper, and the cylindrical parts trace equation is set up by using the coordinate transformation, then simulate the contour and distribution of the trace by using MATLAB. From this model, we found out that the trace of the double-sided lapping is a group of cycloids and the cycloids distribution scope and distribution state have a direct relationship with the drive ratio of fixture. It is found that the track curves are concentric circles with changing time, i.e. when m = 0.3 or m = 1, the inhomogeneity of track curves are increased with changing time when m = 2, The trace curves of lapping are dense and uniform when m = –2. Based on this, placing the cylindrical parts in the middle area of the cycloids when m = –2 is favourable to lapping uniformly.