Protrusion Topography Research Articles

In-process monitoring of microscale grain protrusions by tracing impulse-discharge energy related to thermal transmission balance on diamond cutting interface

Stable ground surface depends on abrasive grain protrusions, but it has no way to monitor the wheel topographical state during grinding. Generally, the charge coupled device (CCD) monitoring is employed to on-machine measure 2D grain protrusions, but the whole wheel micro-topography has not been recognized in-process. In the electro-contact discharge (ECD) truncating of diamond wheel, a thermal transmission balance on diamond cutting interface is proposed to identify the diamond thermochemical removal. Accordingly, the impulse-discharge energy is characterized by discharge waveforms to relate to the microscale grain protrusion topography. The objective is to advance surface grinding by in-process monitoring the whole protrusion topography rather than by on-machine measuring the partial wheel topography. First, the grain top height and area were modeled by the microscale spark-discharge gap and the microsecond grain truncating duration, respectively; then, the influence of kinematic variables and electrical variables on discharge parameters was analyzed to regulate the impulse-discharge energy; finally, the thermochemical removal rate was traced along with the grain protrusion parameters for ground surface quality. It is shown that the diamond thermochemical removal may be regulated by kinematic variables and electrical variables. At the dynamic thermal transmission balance of impulse-discharge energy on diamond cutting interface, the thermochemical removal rate gradually tends to zero, leading to stable grain top height and area for a stable ground surface. As a result, the grain top height and area on the whole wheel surface may be monitored under the critical discharge parameters in relation to grain size during ECD truncating.

Study on copper protrusion of through-silicon via in a 3-D integrated circuit

The through-silicon via (TSV) approach is crucial for three-dimensional integrated circuit (3-D IC) packaging technology. However, there are still several challenges in the TSV fabrication process. One of the widely known challenges is via protrusion phenomenon. Annealing a TSV wafer makes the copper (Cu) TSVs under high stress and may form a protrusion where the Cu is extruded out of the TSV structure. The phenomenon occurs because of the large mismatch in the coefficient of thermal expansion between Cu via and silicon (Si) layer. Cu protrusion is able to cause crack, delamination of the back-end-of-line and short circuit of the chip, thus, it is a dangerous threat to the metal layer interconnect. Experiments are conducted to characterize the protrusion using several techniques. Scanning electron microscope is used to observe the protrusion topography and measure the height. Electron backscatter diffraction (EBSD) technique is implemented to study the grain size distribution, local texture and microstructure evolution inside Cu vias. For the experiment, arrays of 10 μm diameter TSVs are fabricated and annealed in argon gas environment in six different temperatures. In this paper, finite element analysis (FEA) is carried out to study the Cu protrusion under different annealing conditions. Correlation between numerical results and experimental data is then performed. Based on the verified FEA methodology, several parametric studies are then conducted, including the effects of annealing temperature on Cu protrusion, residual stress distributions of TSV structures. The simulation results are helpful to understand and solve the key problem in TSV fabrication process and reliability challenge.

Study on micro-topographical removals of diamond grain and metal bond in dry electro-contact discharge dressing of coarse diamond grinding wheel

A coarse diamond grinding wheel is able to perform smooth surface grinding with high and rigid grain protrusion, but it is very difficult to dress it. Hence, the dry electro-contact discharge (ECD) is proposed to dress #46 diamond grinding wheel for dry grinding of carbide alloy. The objective is to understand micro-topographical removals of diamond grain and metal bond for self-optimizing dressing. First, the pulse power and direct-current (DC) power were employed to perform dry ECD dressing in contrast to mechanical dressing; then the micro-topographies of diamond grains and metal bond were recognized and extracted from measured wheel surface, respectively; finally, the relationship between impulse discharge parameters and micro-topographical removals was investigated with regard to grain cutting parameters, dry grinding temperature and ground surface. It is shown that the dry ECD dressing along with spark discharge removal may enhance the dressing efficiency by about 10 times and dressing ratio by about 34 times against the mechanical dressing along with cutting removal. It averagely increases grain protrusion height by 12% and grain top angle by 23%, leading to a decrease 37% in grinding temperature and a decrease 46% in surface roughness. Compared with the DC-25V power along with arc discharges, the Pulse-25V power removes the metal bond at 0.241mm3/min by utilizing discharge energy by 73% and diamond grain at 0.013mm3/min through surface graphitization, respectively, leading to high and uniform grain protrusion. It is confirmed that the impulse discharge parameters are likely to control the microscopic grain protrusion topography for efficient dressing according to their relations to the micro-removal of metal bond.

Modeling and evaluating of surface roughness prediction in micro-grinding on soda-lime glass considering tool characterization

The current research of micro-grinding mainly focuses on the optimal processing technology for different materials. However, the material removal mechanism in micro-grinding is the base of achieving high quality processing surface. Therefore, a novel method for predicting surface roughness in micro-grinding of hard brittle materials considering micro-grinding tool grains protrusion topography is proposed in this paper. The differences of material removal mechanism between convention grinding process and micro-grinding process are analyzed. Topography characterization has been done on micro-grinding tools which are fabricated by electroplating. Models of grain density generation and grain interval are built, and new predicting model of micro-grinding surface roughness is developed. In order to verify the precision and application effect of the surface roughness prediction model proposed, a micro-grinding orthogonally experiment on soda-lime glass is designed and conducted. A series of micro-machining surfaces which are 78 nm to 0.98 μm roughness of brittle material is achieved. It is found that experimental roughness results and the predicting roughness data have an evident coincidence, and the component variable of describing the size effects in predicting model is calculated to be 1.5×107 by reverse method based on the experimental results. The proposed model builds a set of distribution to consider grains distribution densities in different protrusion heights. Finally, the characterization of micro-grinding tools which are used in the experiment has been done based on the distribution set. It is concluded that there is a significant coincidence between surface prediction data from the proposed model and measurements from experiment results. Therefore, the effectiveness of the model is demonstrated. This paper proposes a novel method for predicting surface roughness in micro-grinding of hard brittle materials considering micro-grinding tool grains protrusion topography, which would provide significant research theory and experimental reference of material removal mechanism in micro-grinding of soda-lime glass.

3D Noise Generation and Removal of Measured Grinding Wheel Topography Using a White Light Interferometer

In order to precisely measure grain protrusion topography of diamond grinding wheel, the measured noises should be removal, but it has not been clear how these noises are produced. Hence, a white light interferometer was employed to measure the SD60 grinding wheel surface. The objective is to evaluate the grain protrusion parameters. It is shown that the noise generation is related to the orientation of measured point. The noise occurs as its vector angle is less than 45°. Moreover, the grain protrusion topography may be displayed though noise removal, noise-data restructure and grain contour protection. The grain protrusion height, bond-tail height, rake angle and clearance angle are averagely 108.2 μm, 49.1 μm, -68.6º and 26.4º, respectively.

3D laser investigation on micron-scale grain protrusion topography of truncated diamond grinding wheel for precision grinding performance

A grain tip (GT) truncation is proposed to truncate grain protrusion tips of #270 diamond grinding wheel in plunge grinding of hard and brittle material. In this study, a 3D laser microscopy was employed to measure the wheel working surface and parameterize its 3D grain protrusion topography. The objective is to investigate how micron-scale grain protrusion parameters influence grinding performance such as grinding force and surface roughness. First, the GT truncation was performed after dressing of diamond grinding wheel in grinding experiment of quartz glass; then its 3D grain protrusion topography was constructed by smoothing 3D measured noise, matching measured point cloud, transferring protrusion frame and extracting 3D diamond grains; finally, the grain protrusion parameters such as grain protrusion number, grain protrusion height, grain protrusion volume, grain rake angle, grain clearance angle, etc. were investigated in connection with ground surface and grinding force. It is shown that GT truncation averagely decreases grain protrusion number, grain protrusion height, grain protrusion volume, grain rake angle and grain clearance angle by about 44%, 74%, 75%, 24% and 70% on whole wheel surface, respectively. However, it greatly increases active grain number by about 32 times and active grain volume by about 181 times in actual grinding with the depth of cut in 1 μm, thus leading to a decrease (about 80%) in surface roughness and an increase (about 40 times) in grinding force. It is also found that truncated diamond grain tips are mostly shaped with nanometer-scale tip wedges along grain cutting direction, leading to about 75% very large negative grain rake angles and about 75% large grain clearance angles, thus contributing to ductile-mode grinding. It is confirmed that the active grain number and active grain volume for the actual depth of cut may be regarded as main grain protrusion parameters to evaluate and predict the precision grinding performance of a coarser diamond grinding wheel.

Experimental study on fabrication and evaluation of micro pyramid-structured silicon surface using a V-tip of diamond grinding wheel

A mechanical fabrication of micro pyramid-structured silicon surface is proposed using crossed grooving with a 60° V-tip of diamond grinding wheel. It can obtain high form-accuracy, good surface quality and efficient productivity in contrast to laser machining and etching, and also assure a high aspect ratio in contrast to other mechanical processes. In order to describe its micro-structured topography, a white-light interferometer was employed, and its measured point cloud was matched using an Iterative Closest Point (ICP) algorithm. In micro grinding, a novel CNC mutual-wear truing was first developed to sharpen the wheel V-tip; then, the effects of microscopic wheel topography, silicon crystal-orientation and grinding parameter were investigated on ground micro-topography, truing ratio and material removal ratio; finally, its form-accuracy, pyramid top radius, groove tip radius, surface roughness and aspect ratio were evaluated. It is shown that better microscopic grain protrusion topography on wheel V-tip produces much larger material removal ratio and much better micro-structured topography in micro grinding, but it leads to much less truing ratio in finer GC truing. In micro grinding, silicon crystal-orientation has little effect on micro-structured topography due to diamond crystal-orientations that are randomly distributed on wheel V-tip. Although the micro pyramid-structured form error is only about 3.4 μm, its V-groove bottom and pyramidal top have very large form errors (23.1–47.9 μm) due to the sharpness of wheel V-tip and the frangibility of micro pyramid top. On increasing feed speed, its pyramid top radius decreases and its groove tip radius slightly increases, ultimately leading to an increase in aspect ratio, whereas its surface quality descends. It is concluded that the micro-pyramid arrays may be precisely patterned on silicon surface using a SD600 wheel with crossed tool paths, on-machine V-tip truing and the depth of cut in 1 μm.

Study on axial-feed mirror finish grinding of hard and brittle materials in relation to micron-scale grain protrusion parameters

An axial-feed mirror finish grinding of hard and brittle materials is proposed by controlling grain protrusion parameters. In this grinding, the grinding wheel feed is along the wheel axial direction rather than in the traditional wheel cutting direction. The objective is to understand how micron-scale grain protrusion parameters influence ductile-mode grinding and ultimately to realize efficient mirror finish grinding using a coarse diamond grinding wheel. In this study, the grain tip truncation (GT-truncation) was performed after dressing to improve grain protrusion topography. First, a formation model of axial-feed ground surface was constructed to analyze the effect of grain protrusion parameters and grinding parameters on the critical cutting depth transferred from brittle-mode removal to ductile-mode removal; then GC dressing and GT-truncation of #180 diamond grinding wheel were experimentally performed to investigate surface roughness and ductile-mode grinding behavior with reference to grinding parameters and grain protrusion parameters; finally, a truncated coarser #60 diamond grinding wheel was employed for mirror finish grinding to observe active grain number and grain protrusion angle. Theoretical analysis shows that this ductile-mode grinding is dominated by active grain number, active grain protrusion angle, wheel rotating speed and axial-feed speed, but it does not depend on the depth of cut assumed to be less than the grain protrusion height. Experimental results indicate that the GT-truncation may increase active grain number and grain protrusion angle for ductile-mode grinding when the axial-feed speed decreases to some extent. Moreover, the micro tip radius of diamond grain also influences the ground surface. It is confirmed that by increasing active grain number and grain protrusion angle synchronously, a truncated #60 diamond grinding wheel can be applied for efficient mirror finish grinding of the SiC ceramic plate at the axial-feed speed of 50 mm/min and the tool path interval of 0.1 mm.

3D graphical evaluation of micron-scale protrusion topography of diamond grinding wheel

A new graphical evaluation of micron-scale wheel protrusion topography is proposed by using 3D coordinate data derived from contact measuring of ♯180 diamond grinding wheel. The objective is to quantify 3D distribution of grain protrusion height, gain rake angle and grain relief angle on wheel working surface in dressing. First adaptive measuring was conducted on the base of topographical curvature to identify grain cutting edge in 3D space, second grain protrusion mode was established by polar coordinate transfer so as to ascertain datum plane of grain protrusion, then linear approximation graphics was conducted to display wheel protrusion topography, finally distributions of gain rake angle and grain relief angle were investigated with reference to grain protrusion height. Analytical results show that higher outer grains have more and shaper cutting edges, but lower layer grains retain approximately original crystal forms. In wheel protrusion topography, grain protrusion heights, grain rake angles and grain relief angles are dispersedly distributed in the range 0–28 μm, −45.0° to −89.1° and 1.2–73.1°, respectively, which can be increased by dressing. It is concluded that 3D grain protrusion attitudes distributed on wheel working surface can be quantified by 3D graphical evaluation method.

A Study on Fractal Dimension of Grit Protrusion Topography of Diamond Grinding Wheel

Fractal dimension is proposed to evaluate grit protrusion feature concerning grit protrusion area and length. The aim is to investigate crystal integrate of diamond grit protruded from grinding wheel after dressing. First, 3D crystal diamond grits are established in AutoCAD concerning various crystal configurations. Second, fractal dimension for original diamond grit is analyzed theoretically. Then, dressing experiment is carried out to investigate fractal dimension of grit protrusion topography by suing image processing of SEM photos of dressed grinding wheel surface. Finally, grit protrusion feature is investigated by fractal dimension concerning the depth of cut in dressing process. It is confirmed that fractal dimension can display grit protrusion feature and it may be used to evaluate dressing performance.

A Study on Surface Generation of Metal-Bonded Diamond Grinding Wheel Dressed by Electro-Contact Discharge

This paper conducted Electro-Contact Discharge (ECD) dressing experiment for #600 diamond grinding wheel to understand how fine diamond grits protrude from metal-bonded wheel surface. The SEM observation, EDS analysis, image processing and 3D grit modeling on wheel surface were carried out to investigate grit protrusion characteristics. Then ECD dressing and mechanical dressing experiments were carried out to identify the effect of grit protrusion feature on grinding performance. It is confirmed that the dressed wheel surface topography is sensitive to open circuit voltage Ei, discharge polarity and electrode composition. Meanwhile, ECD dressing with Ei=15V and straight polarity can produce superior protrusion topography without the damage of diamond crystal faces and the bond tail behind protrusive grit. It can obtain better ground surface of hard-brittle material than mechanical dressing with the bond tail.

Analysis of residual stress in dissimilar HIP-bonded materials : K. Tsutsumi et al (Kobe Steel Co. Ltd., Hyogo, Japan), Kobe Steel Eng. Rep., vol 45, no 1, 1995, 56–59. (In Japanese)

Stable ground surface depends on abrasive grain protrusions, but it has no way to monitor the wheel topographical state during grinding. Generally, the charge coupled device (CCD) monitoring is employed to on-machine measure 2D grain protrusions, but the whole wheel micro-topography has not been recognized in-process. In the electro-contact discharge (ECD) truncating of diamond wheel, a thermal transmission balance on diamond cutting interface is proposed to identify the diamond thermochemical removal. Accordingly, the impulse-discharge energy is characterized by discharge waveforms to relate to the microscale grain protrusion topography. The objective is to advance surface grinding by in-process monitoring the whole protrusion topography rather than by on-machine measuring the partial wheel topography. First, the grain top height and area were modeled by the microscale spark-discharge gap and the microsecond grain truncating duration, respectively; then, the influence of kinematic variables and electrical variables on discharge parameters was analyzed to regulate the impulse-discharge energy; finally, the thermochemical removal rate was traced along with the grain protrusion parameters for ground surface quality. It is shown that the diamond thermochemical removal may be regulated by kinematic variables and electrical variables. At the dynamic thermal transmission balance of impulse-discharge energy on diamond cutting interface, the thermochemical removal rate gradually tends to zero, leading to stable grain top height and area for a stable ground surface. As a result, the grain top height and area on the whole wheel surface may be monitored under the critical discharge parameters in relation to grain size during ECD truncating.