Diamond Grits Research Articles

Thermal Damage of Diamond Grits during the Brazing Process with Ni-Cr Alloy

During the brazing process, the high brazing temperature, the chemical and physical reaction between diamond and alloy, and the residual stress would result in the thermal damage of diamond. The morphology and mechanism of thermal damage is studied when the brazed diamond grits is brazed using Ni-Cr alloy in this paper. The results show that the manifestations of the thermal damage mainly include surface graphitization, erosion pits, microcrack and breaking. The graphitization only occurs on the surface of diamond grits. And the microcrack of diamond grits appears near interface.

Determination of the complex workpiece-to-wheel working surface pressing force restricted by mechanical strength of diamond grits

A method has been proposed for analytical calculation of the pressing force of a complex steel/hardmetal workpiece against the wheel working surface, which is restricted by the diamond grit strength, in elastic-mode infeed surface grinding.

Influence of Zinc Particles on Oxidation Resistance of Diamond/Borosilicate Glass Composites

Oxidization of diamond in the sintering process of diamond/borosilicate glass composites would result in low compressive fracture strength (CFS) of the grit and uncontrolled expansion with many irregular pores in the composites, causing low bending strength of the tools. In this paper diamond/borosilicate glass composites were prepared by cold pressing and sintering at 850 C for 120 min in air. An active element Zn was incorporated into the composites in order to resolve the above issues. The effects of Zn contents on the properties of the composites was investigated by the bending strength tests, the volume expansion rate tests, differential scanning calorimeter test (DSC), thermogravimetry (TG), X-ray diffraction analysis (XRD), and scanning electron microscope (SEM). The results showed Zn was oxidized and then converted to ZnAl2O4 and Zn2SiO4 phases during sintering. The bending strength improved and the expansion phenomenon was inhibited for the composites with various Zn additions. The maximum bending strength and minimum volume expansion rate were obtained for the composite GZ8. This Zn content resulted in a decrease of volume expansion rate from 8.57% to -20.53%, and an increase in bending strength from 28.49 MPa to 74.02 MPa compared with the composite GZ0. The CFS results of the diamond grits separated from GZ0 and GZ8 was 21N and 26N, respectively.

A Comparative Study: Tool Life and Wear of Thin-Walled Monolayer Brazed Diamond Core Drill Fabricated with Ni-Cr and Ag-Cu-Ti Alloy

Monolayer brazed diamond tools, which are high bonding strength at the interface between brazing alloy and grits, are becoming the active field in which improvements in processing and advanced products can be anticipated. Some researchers proposed brazing diamond methods with Ni-Cr and Ag-Cu-Ti alloy, but there is a shortage of the comparative study of the characteristics of the brazed diamond tools fabricated with the different brazing alloy. In this paper, machining performance experiments have been carried out, including contrast tests about tool life and machining efficiency for thin-walled monolayer brazed diamond core drills fabricated with Ni-Cr and Ag-Cu-Ti alloy. The results show that the Ag-Cu-Ti alloy can improve the machining performance. Wear mechanism of diamond grits was studied in those drilling processes. The results show that the low ratio of grit breakdown of the core drill using Ag-Cu-Ti alloy is the key factor of its longer life. Furthermore, based on the experimental results, the areas of the grits wear flat increase the feed force, and decrease the machining efficiency.

Effect of Dressing Load and Speed on Removal Rate in the Chemical Mechanical Polishing Process

A pad conditioner or diamond disk is needed to regenerate the asperity structure of the pad and recover its designated role in the chemical mechanical polishing process. In this paper, the effect of dressing load and speed on removal rate of oxidized wafers were investigated using a polycrystalline diamond disk and brazed diamond disk. It was found that polycrystalline diamond disk enable the manufacturer to tightly control diamond leveling and the cutter’s shape by comparison with a brazed diamond disk that contains discrete diamond grits of random orientation. Experimental results revealed that for polycrystalline diamond disk, the removal rate of oxidized wafer displayed an almost unchanged curve when the load was less than 4kg, but the removal rate of oxidized wafer for brazed diamond disk initially increased with the dressing load, reaching a maximum value at a dressing load of approximately 4 kg. Then, it decreased slowly with further increases of the dressing load. The removal rate of oxidized wafer remains unchanged with dressing speed.

Optimization of Process Parameters in CFRP Machining with Diamond Abrasive Cutters

The present paper proposes a methodology to optimize process parameters for trimming applications with diamond abrasive cutters. This methodology is based on the study of quality of trimmed surface, through material integrity and surface roughness, and on the study of cutting mechanisms. Their evolutions according to tool parameters and cutting conditions have been analysed. Results show that diamond grits size must be chosen according to the required surface roughness. Feedrate must respect cutting limitations due to CFRP removal mechanisms with abrasive cutters, which have been identify through analyses of specific cutting energy. Finally, a protocol in two steps is proposed to determine the optimum process parameters according to the application. Firstly, constraint functions due to respect of quality and to limiting cutting phenomena are defined. Thus, limiting values of process parameters are determined. Then, process parameters are selected in order to optimize productivity.

Depression Effects of Al on Oxidation of Diamond During Sintering of Diamond/Borosilicate Glass Composites

Oxidization of diamond in the sintering process of diamond/glass composites results in uncontrolled expansion with many irregular pores and low bending strength of the tools. In this paper, Al powder was used as oxygen getter due to its excellent affinity with oxygen. Its oxidization product, Al2O3, entered into glass network. Consequently, oxidization of the grits was inhibited, and the wettability of diamond grits by the matrix improved. As a result, the expansion phenomenon was inhibited and the bending strength improved for all the composites. The minimum volume expansion rate and maximum bending strength were obtained for the composite with 4 wt% Al powder. This Al content resulted in a decrease of volume expansion rate from 175.2% to −10.9%, and an increase in bending strength from 11.3 to 75.1 MPa compared with the composite without Al powder.

Evaluation Method Applying Fourier Transform Analysis for Conditioned Polishing Pad Surface Topography

The Fourier transform analysis is proposed to quantitatively evaluate the 3D surface topography of Chemical Mechanical Polishing (CMP) pads used for flattening and smoothing processed semiconductor substrates. The conditioned polishing pad surfaces have a wide range of irregular topographies ranging from topographies of a sub-micrometer to those of a hundredmicrometer order. Hence, a Confocal Laser Scanning Microscope (CLSM), which can provide nanometer resolution in wide range of lateral directions by means of linear encoded mechanical stage translation, was employed to obtain numerical data of the three-dimensional topographic surfaces of polishing pad samples. The measured topographic surfaces were analyzed using the spatial Fourier transform. We discuss the power spectrum in the spatial wavelengths of polishing pad surfaces which were conditioned with diamond grits of various shapes. The analyzed power spectra indicated that the surface topography characteristics varied with differently shaped diamond grits of the same size. The diamond grits roughened the polishing pad surface. We also found that a rough polishing pad surface, one that was roughed in a spatial wavelength that of less than 20 micrometers, removed more material than comparatively smooth pad surfaces.

Experimental Study on the Surface Roughness with Mill-Grinding SiC Particle Reinforced Aluminum Matrix Composites

In view of the present machining status of SiC particle reinforced aluminum matrix composites, the electroplated diamond wheel (80# diamond grit) was used for mill-grinding the SiC particle reinforced aluminum matrix composites and the effect of speed ratio (q) and material removal rate (MRR) on surface roughness was studied based on experiments. The experimental results show that surface roughness almost increases with the increase of speed ratio. At the same material removal rate, surface roughness increases when raising material removal rate by raising feed rate singlely or raising depth of mill-grinding singlely; surface roughness has decreasing trend with raising material removal rate by increasing feed rate and depth of mill-grinding at the same time.

Novel CVD diamond-coated conditioner for improved performance in CMP processes

Conditioning of polishing pads during chemical mechanical planarization (CMP) of wafers is a critical process for maintaining productivity and quality control in the semiconductor industry. This investigation aims at developing a CMP diamond conditioner of a new concept and hence improving the conditioning performance. The novel diamond conditioner was fabricated by coating diamond films on a Si 3N 4 substrate with regularly patterned protrusions. Thanks to the uniform distribution and constant height of protrusions, the novel conditioner exhibited superior performance and durability over the current conditioner, which contains bonded diamond grits of various sizes and shapes with unequal heights. Characterization of the developed novel diamond CVD conditioner has also been made.

Development of a novel custom micro-tool for effective cutting of a precision microgroove array on a microscope slide

This study presents a novel, economical and efficient fabrication technique for precisely generating multiple microgrooves on a microscope slide to allow for microscopic examination of urine sediment cells. This study incorporates two important phases: a precision wheel-tool array is fabricated and then the developed tool is used in fast on-line grinding of multiple microgrooves. The wheel-tool blank is made of diamond grit of 0–2 µm grade via co-deposition. Subsequently, it is trued, sliced and sharpened by means of micro wire electro discharge dressing. The finished wheel-tool is utilized on-line to grind multiple microgrooves using ‘high-speed and fast-shallow grinding’. A ductile grinding regime is established to obtain a nano-metric surface finish for the multiple microgrooves generated on the microscope slide. The depth and width of the grooves in the array are both 10 µm and a surface finish of Ra equal to 0.010 µm is simultaneously achieved. This multiple microgrooving technique can supply high-quality fast grinding in the fabrication of bio-medical devices, such as those used for stationing and counting urine sediment cells.

Fabrication of grinding tool material by the SHS of Ni–Al/diamond/dilute

A mixture of Ni–Cr–P, Cu and B powder was used as a dilute for modifying the microstructure of the reacted product and easing the fast propagating rate and the high temperature in the self-propagating high-temperature synthesis (SHS) of Ni–Al matrix grinding tool material. The SHS process of the Ni–Al/diamond/dilute was examined and the microstructure of the reacted product was analyzed by X-ray diffraction (XRD) and scanning electron microscopy (SEM). The grinding performance of the tool was tested in the grinding of a synthetic single crystal of sapphire. The results showed that the dilute substantially reduced the propagating rate and the combustion temperature of Ni–Al SHS. Besides the dominating intermetallics NiAl and NiAl 3, Ni 4Al 3 was also identified in the reacted Ni–Al/diamond/dilute composite owing to the Ni rich environment. In the reacted composite there was a Cr-rich zone at the boundary of the diamond grit due to the formation of Cr 3C 2 between Cr and the diamond. In the grinding a lower wear rate and a better retention ability of diamond grits could be achieved for the grinding tool material that contained finer diamond grits.

Micro/nano Indentation and Single Grit Diamond Grinding Mechanism on Ultra Pure Fused Silica

The existing research about ductile grinding of fused silica glass was mainly focused on how to carry out ductile regime material removal for generating very "smoothed" surface and investigate the machining-induced damage in the grinding in order to reduce or eliminate the subsurface damage.The brittle/ductile transition behavior of optical glass materials and the wear of diamond wheel are the most important factors for ductile grinding of optical glass.In this paper,the critical brittle/ductile depth,the influence factors on brittle/ductile transition behavior,the wear of diamond grits in diamond grinding of ultra pure fused silica(UPFS) are investigated by means of micro/nano indentation technique,as well as single grit diamond grinding on an ultra-stiff machine tool,Tetraform "C".The single grit grinding processes are in-process monitored using acoustic emission(AE) and force dynamometer simultaneously.The wear of diamond grits,morphology and subsurface integrity of the machined groves are examined with atomic force microscope(AFM) and scanning electron microscope(SEM).The critical brittle/ductile depth of more than 0.5 μm is achieved.When compared to the using roof-like grits,by using pyramidal diamonds leads to higher critical depths of scratch with identical grinding parameters.However,the influence of grit shapes on the critical depth is not significant as supposed.The grinding force increased linearly with depth of cut in the ductile removal regime,but in brittle removal regime,there are large fluctuations instead of forces increase.The SEM photographs of the cross-section profile show that the median cracks dominate the crack patterns beneath the single grooves.Furthermore,The SEM photographs show multi worn patterns of diamond grits,indicating an inhomogeneous wear mechanism of diamond grits in grinding of fused silica with diamond grinding wheels.The proposed research provides the basal technical theory for improving the ultra-precision grinding of UPFS.

Effect of CMP conditioner diamond shape on pad topography and oxide wafer performances

Chemical mechanical polishing (CMP) performance is often determined by the pad surface texture, which is mainly controlled by using a pad conditioner: usually, a diamond disk comprising numerous diamond grits attached to a flat metal substrate by means of brazing with an alloy. During the conditioning process, the diamonds interact with the pad surface to mainly remove the glazed layer and restore pad asperities. Selection of the appropriate diamond shape is crucial for obtaining the desired pad properties, conditioner life, and wafer removal rate. In this investigation, three different diamond shapes were carefully fabricated: (1) “sharp,” a sharp-edged diamond; (2) “blocky,” a high-quality crystalline diamond; and (3) “mixed,” a combination of sharp and blocky diamonds. Three new disks were fabricated using the above mentioned diamond shapes. Pad surface characterization was carried out to compare the new disks with conventional diamond disks, and the effect of the diamond shape on the wafer removal rate was studied. Oxide CMP tests revealed that the “mixed” diamond grit provided the highest wafer removal rate and the best uniformity. As compared to a conventional diamond disk, it also achieved a higher wafer removal rate and a better uniformity while consuming less pad material. On the other hand, if the dressing stability is the major concern, the use of “blocky” diamond grit is recommended because it provided the most stable wafer removal rate over a conditioning time of up to 20 h. However, if the dressing capability is the major concern, the use of “sharp” diamond grit is suggested because it provided the highest pad cut rate.

Investigation of a Novel Diamond Disk's Effect on Pad Topography in Oxide Chemical Mechanical Polishing

Polishing pads become glazed due to the accumulation of debris during chemical mechanical polishing (CMP) processes. Hence, the wafer removal rate is reduced. A pad conditioner or diamond disk must be frequently employed to restore the pad surface texture. Traditional diamond disks are prepared by adhering similar types of diamond grit to a flat substrate. In these cases, the diamond tips have different heights due to difficulties in controlling the levels of such large amounts of diamond grit. In this study, a new combined diamond disk is designed and manufactured to significantly improve the leveling of diamond tips, thereby reducing the amount of diamond grit. The proposed combined diamond disk incorporates two types of diamond grit (blocky and sharp) distributed across the entire disk surface. Such a combined diamond disk enables the manufacturer to tightly control diamond leveling and, moreover, reduces the number of diamond pieces by more than a factor of two. Experimental results reveal that that the removal rate correlates well with variations in force. The combined diamond disk provides a higher polishing rate and better uniformity while consuming less pad material. The pad lifetime is expected to be prolonged, and this consequently lowers the operational costs of the CMP process.

Joining of Diamond Grains to Medium Carbon Steel with Ni-Base Powder during Laser Brazing

In order to develop new generation brazed Diamond grinding wheels, the joining experiments of Diamond super abrasive grains and medium carbon steel using the powder mixture of Ni-Cr alloy as active brazing alloy are carried out via laser in an argon atmosphere. The relevant characteristics of the special powder mixture, the microstructure of the interfacial region, which are both the key factors for determining the joining strength among the Diamond grains, the filler layer and the steel substrate, are investigated extensively by means of scanning electron microscope (SEM) and energy dispersion spectrometer (EDS), as well X-ray diffraction (XRD) analysis. The formation mechanism of carbide layers was discussed. All the results indicate that high strength bonding between diamond grits and the steel substrate has been successfully realized because the chromium in the Ni-based alloy segregated preferentially to the surface of the diamond to form a chromium-rich reaction product Cr3C2, and the bond between the alloy and the Diamond was established through the reaction product.

Anisotropic mechanical amorphization drives wear in diamond

Diamond is the hardest material on Earth. Nevertheless, polishing diamond is possible with a process that has remained unaltered for centuries and is still used for jewellery and coatings: the diamond is pressed against a rotating disc with embedded diamond grit. When polishing polycrystalline diamond, surface topographies become non-uniform because wear rates depend on crystal orientations. This anisotropy is not fully understood and impedes diamond's widespread use in applications that require planar polycrystalline films, ranging from cutting tools to confinement fusion. Here, we use molecular dynamics to show that polished diamond undergoes an sp(3)-sp(2) order-disorder transition resulting in an amorphous adlayer with a growth rate that strongly depends on surface orientation and sliding direction, in excellent correlation with experimental wear rates. This anisotropy originates in mechanically steered dissociation of individual crystal bonds. Similarly to other planarization processes, the diamond surface is chemically activated by mechanical means. Final removal of the amorphous interlayer proceeds either mechanically or through etching by ambient oxygen.

Amorphous Diamond Solar Cells with Nanodiamond Quantum Wells

Thin film solar cells have emerged in recent years, in particular, those made of amorphous silicon or CIGS (copper indium gallium sellenide). By tendon of boron doped amorphous diamond with phosphorus doped amorphous silicon, the conversion efficiency may rival that of crystalline silicon. On the other hand, the CdS top layer for CIGS is not only poisonous, but also UV degradable. Amorphous diamond coating with N doping can replace CdS to boost CIGS's efficiency also. Nanodiamond may be sputtered from diamond grit or diamond film as target. The PVD formed nanodiamond layer can be located at the interface between P and N types. In this case, the quantum well effect can allow the production of multiple electrons per incident photon. In addition, the output voltage may be increased due to the wide band gap of nanodiamond.

Mosaic Diamond Pad Conditioners for Improved CMP Performance

A mosaic design of diamond disks that incorporates different cutting characteristics of diamond grits can allow faster polishing of wafers with less pad consumption. Larger diamond grits can make pad asperities with large peak to valley ratios for achieving high polishing rate. On the other hand, Sharp grits can shave the pad effectively as to eliminate the glazed layer. The conventional diamond disks employ similar type of diamond grits across the entire disk. These grits cannot dress and cut the pad with optimization. By combining different types of diamond grits in a cocktail combination, the pad asperities can be controlled to enhance removal rates of the wafer. The glazed layer may also be removed cleaner so wafer defectivity is minimized.

The Pad Dressing Phenomena of Multiple Diamond Grits: Implications for the Design of CMP Pad Conditioners

Diamond disks are indispensable for dressing CMP pads. However, due to the poor leveling of diamond tips, only a few percents of diamond grits can penetrate the pad. As these few crystals are worn out, the plastic deformation of the pad becomes large relative to the amount of pad is cut. The polishing rate will then decline; and the scratch rate, increase. A novel technique has been developed to identify the cutting tips and their dulling process. The cutting paths become widen and shallow with more and more deformed pad material. Eventually, fewer and fewer scratch lines are present with most touching diamond pushing deformed pad around. Because there are only a handful of diamond grits that are engaged in cutting pad, the number of working crystals can increased substantially by improving the leveling of diamond tips. This improvement can increase the longevity of diamond disks that paves the way for future CMP of 18 inches wafers scheduled to make the debut in 2012.