Fixed Abrasive Pad Research Articles

A Novel Noise Reduction Approach of Acoustic Emission (AE) Signals in the SiC Lapping Process on Fixed Abrasive Pads.

Acoustic emission (AE) technology has been widely utilized to monitor the SiC wafer lapping process. The root-mean-square (RMS) of the time-domain eigenvalues of the AE signal has a linear relationship with the material removal rate (MRR). However, the existence of background noise severely reduces signal monitoring accuracy. Noise interference often leads to increased RMS deviation and signal distortion. In the study presented in this manuscript, a frequency threshold noise reduction approach was developed by combining and improving wavelet packet noise reduction and spectral subtraction noise reduction techniques. Three groups of SiC lapping experiments were conducted on a fixed abrasive pad, and the lapping acoustic signals were processed using three different noise reduction approaches: frequency threshold, wavelet packet, and spectral subtraction. The results show that the noise reduction method using the frequency threshold is the most effective, with the best coefficient of determination (R2) for the linear fit of the RMS to the MRR.

In-situ reconditioning mechanism for fixed abrasive pads based on the wear behavior of loose grains

C-plane sapphire (α-Al2O3) is a commonly used substrate material for integrated circuits and Light-emitting diodes (LEDs). Efficient, stable, and low-damage lapping processes are used to ensure surface smoothness and meet application requirements. Fixed abrasive pads (FAPs) are typically used for the lapping of sapphire substrates, but the pads are prone to be glazed or even failed. In this study, loose alumina grains were used for in-situ reconditioning of fixed diamond abrasive pads. The material removal rate and surface roughness of the lapped sapphire substrate were calculated, the types and size distributions of the wear debris were analyzed, the surface morphology of the FAP after lapping was examined, and an online monitoring system was used to track the friction coefficient between the FAP and the sapphire substrate. In order to determine the ideal size and concentration of loose grains and to reveal the in-situ reconditioning mechanisms for the fixed diamond abrasive pads, the effects of the size and concentration of loose alumina grains in the lapping slurry on the in-situ reconditioning of the FAP were investigated. This was done by examining the wear behavior of loose alumina grains during the lapping processes of sapphire substrates.

Kinematics and trajectory analysis of swinging fixed abrasive plane lapping: Effect of swinging mode on the lapping uniformity

The relative motion between the workpiece and the fixed abrasive pad (FAP) determines the abrasive trajectories and the distribution of abrasives' sliding distance (ASD), and further affects the surface accuracy of the lapping process. To improve the surface accuracy of the swinging fixed abrasive plane lapping (SFAPL), the influence of the workpiece's swinging modes on the lapping uniformity was studied in this paper. The kinematics model of SFAPL was established by the coordinate transformation method based on the kinematical principle of the crank-rocker mechanism. The numerical simulation method was adopted to investigate the abrasive trajectories and the ASD on the workpiece surface in different swinging modes. Furthermore, the regional meshing and statistical methods were applied to visualize the simulation results, and the non-uniformity coefficient (NUC) and root mean square (rms) were employed to quantitatively evaluate the lapping uniformity. Finally, the verification experiments were carried out. Results indicated that the additional swinging could avoid the periodic distribution of material removal on the workpiece surface. The swinging mode significantly affected the lapping efficiency and lapping uniformity. Compared with the traditional lapping method, the lapping uniformity was optimal when the workpiece swung out of the FAP from the bottom and inner sides, and the lapping uniformity could be improved by 44.3 %; The lapping efficiency was the highest when the workpiece swung out of the FAP from the bottom side, and the material removal rate could be increased by 45.23 %. The appropriate swinging mode should be selected based on different processing requirements in SFAPL.

An Exploration of the Influence of Abrasive Water Jet Pressure on the Friction Signal Characteristics of Fixed Abrasive Lapping Quartz Glass Based on HHT

Abrasive water jetting is an effective dressing method for a fixed abrasive pad (FAP) and can improve FAP machining efficiency and the impact of abrasive water jet (AWJ) pressure on the dressing effect; moreover, the machining state of FAP after dressing has not been thoroughly studied. Therefore, in this study, the FAP was dressed by using AWJ under four pressures, and the dressed FAP was subjected to lapping experiments and tribological experiments. Through an analysis of the material removal rate, FAP surface topography, friction coefficient, and friction characteristic signal, the influence of AWJ pressure on the friction characteristic signal in FAP processing was studied. The outcomes show that the impact of the dressing on FAP rises and then falls as the AWJ pressure increases. The best dressing effect was observed when the AWJ pressure was 4 MPa. In addition, the maximum value of the marginal spectrum initially rises and then falls as the AWJ pressure increases. When the AWJ pressure was 4 MPa, the peak value of the marginal spectrum of the FAP that was dressed during processing was the largest.

Super hard and brittle material removal mechanism in fixed abrasive lapping: Theory and modeling

Currently, the problems of inefficient fixed abrasive lapping (FAL) for super hard and brittle material wafers (such as sapphire) with fixed abrasive pads (FAPs), restrict the development of the semiconductor industry. Most importantly, the mechanisms of FAL processes are still unclear, often analyzed based on the theoretical models of chemical mechanical polishing (CMP). However, the material removal models of CMP are specific to loose abrasives, do not effectively apply to the lapping processes for super hard and brittle material wafers with a FAP. In this paper, the spherical crown model modified by elastic-plastic mechanics and brittle-plastic transformation mechanism was applied to super hard and brittle material removal mechanism in FAL processes. In consideration of the influences of the yielding abrasives embedded in the FAP matrix and the matrix surface topography on the wafer-pad contact, a material removal model suitable for super hard and brittle material wafers lapped by FAPs was obtained. The loads applied on the fixed abrasives and the matrix asperities during the elastic-plastic-brittle deformation processes of wafers were analyzed, respectively. The model indicates that the back-off of the abrasives embedded in the FAP matrix intensifies along with the decrease of the matrix hardness and the increase of the abrasive size, respectively. The penetrating depth of the fixed abrasive can be raised by increasing matrix hardness, applied pressure, abrasive size, and decreasing abrasive number, as same as the elastic recovery of the super hard and brittle material slid by the abrasive after unloading. The pad matrix surface dressed by loose grains greatly affects the MRR of wafers. The predicted MRR of sapphire wafers based on the FAL model is consistent with experimental data. Finally, the keys to improving the processing efficiency of super hard and brittle material wafers are clarified in detail.

Process Parameter Modeling and Optimization of Abrasive Water Jet Dressing Fixed-Abrasive Pad Based on Box-Behnken Design.

Clarifying the influence of the dress process parameters of the abrasive water jet on the dressing effect of fixed-abrasive pads (FAPs) is a prerequisite for online controllable dressing of abrasive water jets. This paper uses three factors and three horizontal response surface methods to explore the influence of jet pressure, abrasive concentration, and nozzle angle on FAP dressing quality. The prediction model of the material removal rate of a FAP machined using three process parameters is established. The influence of pairwise interactions of the three process parameter variables on the dressing effect and the optimal process parameters under each target is analyzed. Finally, the optimal process parameters predicted by the model are verified by experiments. The results show that the best dressing parameters with the MRR of the workpiece as the response value are as follows: jet pressure 3.8 MPa, abrasive concentration 3%, and nozzle angle 73°. The predicted value of the optimal process performance is 464.574 nm/min, and the experimental verification result is 469.136 nm/min; the error between the experimental value and the predicted value is within a reasonable range.

Machining Stability Research of Soft-Brittle Crystals Lapping by Fixed-Abrasive Pad

Fixed-abrasive (FA) lapping and polishing process is the main approach to realize the residual-free and low damage processing of soft-brittle crystals. The hardness of matrix and the abrasive micro-fragmentation are the key parameters impacting the stability of the continuous batch machining. The FA pads were prepared with hard and soft matrix, respectively, and the single diamond (SD) and the aggregated diamond (AD) were mixed in the FA pads, respectively. The FA lapping tests were carried out with LN wafers under the applied load of 10.5 kPa. The continuous batch machining stability of four pads tests were evaluated by the evaluation indexes of the material removal rate (MRR), surface roughness Ra and the material removal rate variation (MRRV). The workpiece surface morphology and abrasive wear pattern were analyzed. The results indicate that: hard matrix is not conducive to the shedding and replacement of abrasive grains because of the high holding force, causing a MRRV of 50%. The MRR of the hard matrix pad tests signally decrease from 3.71 μm/min to 1.9 μm/min. By contrast, the low hardness matrix pad can be applied to improve the machining efficiency owing to its MRRV only about 30%. The MRR of the AD pad is over 600 nm/min, which is far more than that of the SD pad, and the MRRV of the AD pad is just about 20%. While MRRV of the SD pad is as high as 75% with the remarkably decline of MRR. At the view of Ra values, the SD pad and the AD pad both attain nanoscale. The Ra values of the SD pad tests are smaller and the workpiece are superior in surface quality. In the rough lapping and fine lapping stage, the SD can be used to prepare FA pad to improve lapping stability.

Study on Wavelet Packet Energy Characteristics on Friction Signal of Lapping with the Fixed Abrasive Pad.

The surface condition of the fixed abrasive pad (FAP) has a significant impact on its machining performance, workpiece material removal rate (MRR), and surface roughness. To clarify the wavelet packet energy characteristics of friction signal under different surface conditions of FAP and its mapping relationship with MRR and workpiece surface quality, FAP samples in different processing stages were obtained through a consolidated abrasive grinding quartz glass experiment. Then, the friction signals in different stages were received by the friction and wear experiment between the FAP and quartz glass workpiece, and the wavelet packet analysis was carried out. The experimental results show that with the increase of lapping time, the surface wear degree of the FAP increased gradually, and the MRR of the workpiece, the surface roughness of the FAP, and the surface roughness of the workpiece decreased slowly. In the wavelet packet energy of friction signal during machining, the energy proportion of frequency band 7 showed an upward trend with the increase of lapping time. The energy proportion of frequency band 8 showed a downward trend with the increase of lapping time. The change characteristics of the two are significantly correlated with the surface condition of the FAP.

Tribological effects of loose alumina abrasive assisted sapphire lapping by a fixed agglomerated diamond abrasive pad (FADAP)

The tribological effects between a fixed abrasive pad (FAP) and a workpiece can effectively maintain the self-conditioning process of the FAP in real time. However, the FAP is easy to be glazed along with the long-term lapping processes of hard-to-process ceramic materials. This paper proposed a novel method of loose abrasive assisted fixed agglomerated diamond abrasive lapping (LA-FADAL) to achieve efficient and stable lapping processes of sapphire. LA-FADAL tests with a fixed agglomerated diamond abrasive pad (FADAP) were carried out by changing the particle size and volume fraction of loose alumina abrasives in lapping slurries. The influences of the different alumina abrasives on the processing performance of the FADAP were discussed. Material removal mechanisms in the LA-FADAL processes were proposed based on the tribological effects of loose alumina abrasive assisted sapphire lapping by the FADAP. The loose alumina abrasives with the similar size as the diamond grains embed in the surface of the fixed AD abrasive could not remove sapphire materials directly and effectively by mechanical actions, mainly played a role of dressing the FADAP to enhanced the self-sharpening ability of AD abrasives, and further improved the self-conditioning ability of FADAPs.

High efficiency polishing of silicon carbide by applying reactive non-aqueous fluids to fixed abrasive pads

In pursuing high precision and high-quality surface of silicon carbide (SiC) substrates for electronic applications, however, the processing efficiency on Si-face has long been a difficult challenge compared to that of the C-face. Conventional polishing slurries are aqueous-based due to its unparalleled compatibility with most of chemical reagents, and have been widely studied and well understood. The chemical reactivity of all added accelerating agents in aqueous polishing systems is constrained by the prevalent presence of water as a solvent. On the other hand, non-aqueous polishing systems have not been well explored. In this report, reactive non-aqueous organic systems containing polar hydroxyl groups are evaluated as a high efficiency processing vehicle for Si-face polishing of SiC on fixed abrasive pads (FAPs). The surface quality of SiC is surprisingly improved while the polishing efficiency is accelerated on a diamond FAP in presence of methanol compared to those using water, and are further improved when organic acids are introduced to the reactive non-aqueous fluids. Contact angle measurement and X-ray photoelectron spectroscopy (XPS) analysis on the polished SiC surface are completed to assist us to shed light on the removal behavior and to explore and elucidate the removal mechanism of non-aqueous system fluids on FAPs. The initial positive results from this reactive non-aqueous polishing system serves our community as a promising approach for the ultra-precision polishing on other hard-to-process semiconductor and ceramic materials.

Effect of material structure on spinel machinability in its fixed abrasive lapping

Clarifying the effects of material properties on the lapping performance is helpful in optimizing the lapping processing and revealing the lapping mechanisms. In this study, the microstructures of single-crystal spinel (SS) and polycrystalline spinel (PS) were observed by a microscope after being etched with H3PO4 at high temperature. Automatically controlled micro-hardness testing and analysis systems were used to measure the hardness and crack length of SS and PS wafers. On this basis, the fracture toughness and critical cutting depth were estimated. And, a series of lapping tests were conducted to evaluate the effects of crystals on its machinability with a fixed abrasive pad (FAP). After lapping, the size distribution of collected debris was measured by using a laser particle analyzer. The debris and selected posts of FAP were observed by using a scanning electron microscope. Experimental results indicate that the different microstructures and hardness characteristics between SS and PS result in different average cutting depths, which finally affect the lapping debris sizes, FAP surface conditions, and its machinability.

Lapping performance of mixed-size agglomerated diamond abrasives in fixed abrasives pads

Ultra-fine diamond grains are used to prepare agglomerated diamond (AD) abrasives that are, in turn, applied to make fixed agglomerated diamond abrasive (FADA) pads. The as-prepared pads demonstrated very low removal efficiency along with a poor processing stability，which limits the applicability of ultra-fine diamond grains in fixed abrasive tools. In this reported research, mixed-size agglomerated diamond (MAD) abrasives with a combination of ultra-fine diamond grains and coarser diamond grains were employed to make FADA pads for lapping BK7 glass. Three types of FADA pads were manufactured with ultra-fine AD abrasives, coarser AD abrasives and MAD abrasives, respectively, for maximizing the process efficiency and stability of fixed abrasive pads consisting of ultra-fine diamond abrasives while improving the surface quality of the lapped glass substrates. The results showed that a FADA pad with MAD abrasives exhibited higher material removal rate (MRR) than a pad with AD abrasives of ultra-fine diamond grains only and lower surface roughness Ra and better surface microstructure than a pad with AD abrasives of coarser diamond grains. The distinct lapping feature of MAD abrasives was that the coarser diamond grains mainly accelerate the lapping efficiency while the ultra-fine diamond grains improved the surface quality of workpiece.

Optimal design and experimental study of fixed abrasive pads based on coupling of damping regulation and pellet arrangement

Abstract. Lapping and polishing technology is an efficient processing method for wafer planarization processing. The structure of the fixed abrasive pad (FAP) is one of the most concerning issues in the research. The FAP structure affects the pressure distribution on the wafer surface, and the pressure distribution during processing has a significant influence on the wafer surface. Therefore, in this paper, a better pressure distribution is obtained by adjusting the angle of the spiral arrangement and the damping distribution of the damping layer of the FAP, thereby obtaining better processing quality. Based on the above theory, a new type of FAP, with coupling between the arrangement of the pellets and the damping regulation of the damping layer, was designed and optimized. The machining effects of different FAPs on the workpiece surface are compared in terms of material removal rate, material removal thickness, and surface roughness. The test results show that the workpiece material removal rate is higher than that of the traditional FAP when using the optimized FAP. The non-uniformity of the optimized FAP for that of material removal was 4.034 µm, which was lower than the traditional FAPs by 24.4 % and 17.6 %, respectively. The average surface roughness, Ra, of the optimized FAP is 0.21 µm, which is lower than 19.1 % and 12.5 % of the two traditional FAPs, respectively. Therefore, workpiece material removal and distribution are more uniform, and the surface quality of the workpiece is better when the optimized FAP processing is used. The test results prove that the optimized pellet arrangement and damping can achieve a better surface quality of the workpiece, which can meet the precision lapping process requirements for high-quality surfaces and large-scale production of brittle and hard materials such as sapphire.

Friction and wear characteristics of agglomerated diamond abrasives and lapping performance of fixed agglomerated diamond pads

The friction and wear behaviors of agglomerate abrasive grits in fixed abrasive (FA) pad are closely related to the pad self-conditioning process, which significantly affects its lapping performance and its process stability. In this study, the agglomerated diamond (AD) with two binder concentration were prepared. The prepared single AD grits were then cured into resin posts respectively, and their friction and wear characteristics at different loads by the pin-on-disk test were compared with those of a testing post of single crystal diamonds (SCD). The coefficient of friction (COF) and the cross-sectional area of the wear scars was measured to evaluate the continuous micro-cutting performance of abrasive grits. The worn grits after 30min and 120 min testing were examined by scanning electron microscopy (SEM). The fixed abrasive pads embedded with AD grits were prepared, and their lapping performance at loads of 7 kPa and 14 kPa were evaluated. It could be concluded that the concentration of binders in AD is a key factor in the strength of AD and further influencing the development of micro-fracture in FA lapping process. The higher the strength of AD, the higher the protrusion of AD and less likely to micro-fracturing during FA lapping at the same load. The self-conditioning of the FA pad could be achieved by the synergy of micro-fracturing of AD and wear of the resin matrix.

A novel agglomerated diamond abrasive with excellent micro-cutting and self-sharpening capabilities in fixed abrasive lapping processes

The processing efficiency and stability of ultra-hard and brittle materials plannarized by fixed abrasive pads (FAPs) are largely determined by the cutting depth and the available number of active cutting abrasives and the abrasive wear behaviors. A newly prepared agglomerated diamond (AD) abrasive embedded in FAPs has demonstrated a significant improvement on processing efficiency and stability while being used to lap hard-to-processed ceramic materials. A mathematical model was built to explain the high removal efficiency of the AD abrasives, which followed a similar trend with experimental testing results. The micro-cutting and self-sharpening capabilities of the AD abrasive, which afforded FAPs with AD abrasives to improve efficiency and stability, were manifested by our experimental examinations on the worn abrasive morphologies, the fall-out diamond chips and scratch marks left on sapphire substrates by AD abrasives.

The effect of slurries on lapping performance of fixed abrasive pad for Si3N4 ceramics.

In this paper, a series of experiments were carried out to explore the effect of slurry pH on materials removal rate (MRR) and surface quality in lapping of Si3N4 ceramics wafers with fixed abrasive pad (FAP) using different slurries with different pH. Then, the scanning electron microscope was employed to detect the microtopography and abrade smooth of FAP for exploring the effect of slurries pH on self-conditioning of pad. Experimental results demonstrated that the roughness of wafers increase with the increasing of slurry pH value. The surface of wafers is the best when the pH = 1 and the worst When the pH = 13. The MRR decreases firstly and then decreases with the increasing of the pH. The MRR reaches the lowest when slurry pH = 7, and reaches the highest when slurry pH = 13. These results further suggest that the soften layer of SiO2 could be formed due to the reactions between water and materials on wafer surface, which facilitates increasing material remove rate and improving the surface quality. The hydrogen ion and triethanolamine in slurry could react with the copper in fixed abrasive pad, which also could enhance the materials remove rate and affect the surface quality.

Influence of pellet shape and size on the pattern performance of textured fixed-abrasive pads in single-sided lapping

ABSTRACTLapping with fixed-abrasive pads is regarded as a potentially efficient machining technology due to the precise controllability of abrasive trajectory. For trajectories can be changed by pellet patterns of textured fixed-abrasive pads (T-FAPs), it is essential to studythe influence of pellet shape and size on the pattern performance of T-FAPs. In this paper, different pellet shapes and sizes were studied based on a T-FAP design algorithm in a single-sided lapping, and the pattern performance of T-FAPs was evaluated by the non-uniformity of trajectory (NUT). Based on the results, it is found that pellet shapes and sizes have an obvious influence on the performance of T-FAPs. When circular pellet shape with its size of 4, 8, or 14 mm, NUT value can be lower than 0.08. Therefore, much lower NUT values can be obtained when matching selection of pellet shape and size in pad pattern design.

双图案非均匀耦合固结磨盘的设计及实验研究

双图案非均匀耦合固结磨盘的设计及实验研究

Relationship between mechanical properties and processing performance of agglomerated diamond abrasive compared with single diamond abrasive

Fixed abrasive is taking the place of loose abrasive owing to its high efficiency and little pollution. The self-conditioning ability of fixed abrasive pads (FAPs) plays a favorable role in the lapping process. In this paper, agglomerated diamond (AD) abrasives were prepared for the sapphire lapping process. Material removal rate (MRR), material removal rate variation (MRRV) and surface topography of sapphire wafers lapped by fixed AD abrasive pad were investigated. Abrasive wear and wear debris were characterized. The material removal mechanisms of AD abrasives were discussed. Comparison of mechanical properties between AD and SD in abrasive wear process was analyzed. Influence of mechanical properties of AD abrasives on processing performance was explained. Comparing with fixed single diamond (SD) abrasive pads, the higher MRR, the lower MRRV and surface roughness of sapphire wafer were obtained in the fixed AD abrasive lapping process. Stable large protrusion height and consecutive sharp edges of AD abrasives ensure the excellent lapping performance. The protrusion height of abrasives is positive correlated with the self-conditioning ability of FAPs. The stable protrusion height of AD abrasives is attribute to two points: one is the rough surface of an AD abrasive with multiple sharp cutting edges improves the bonding strength between the abrasives and the pad matrix; the other is the detached diamond particles due to the micro-fracture phenomenon of AD abrasives accelerates the abrasion of matrix.

Mechanism of material removal by fixed abrasive lapping of fused quartz glass

In this paper, a novel fixed-abrasive lapping process to finish off-axis aspheric surfaces efficiently is proposed. The lapping mechanism of fused quartz glass was evaluated using the novel fixed-abrasive pad tool. The applied load and not the rotation speed and feed rate is the key factor affecting the material removal mode of fused quartz glass in the fixed-abrasive lapping process. Analysis of surface characteristic and subsurface damage indicates that lower applied load produces more ductile mode removal and that the removal on fused quartz glass can be changed from brittle fracture to ductile regime if the applied load is less than 25 N. The material removal rate (MMR) increases as the applied load is increased, which further increases the surface roughness. In addition, the MMR increases and the surface roughness decreases as the rotation speed is increased or the feed rate is deceased. A theoretical model for predicting the maximum SSD depth of the specimens during lapping was developed. The model can predict well that the maximum SSD depth increases with increasing applied load.