Wheel Grit Size Research Articles

A Study of the Effect of Back Grind Wheels on Wafer Edge Chippings and Die Strength

The drive for thinner package architecture is already becoming a necessity. There were a need of thinner Integrated Circuit or IC in order to fit in to thinner applications like mobile phones. One of the major semiconductor process that enables miniaturization was wafer back grinding. The process involves wafer thinning to a required thickness with the use of back grinding wheels that serve as the abrasive material. The paper will discuss the effect of back grind input parameters like step grinding and wheel grit size to its output characteristics like total thickness variation, edge chippings and die strength. Total thickness variation will define if the new wheel will not affect the variation with the wafer. On the other hand, edge chippings and die strength will define the reliability of the die on different conditions of the package. Lastly, these 3 characteristics will establish the manufacturability of the process as it will eliminate the probability of wafer breakage.

Multi-Objective Optimization of the Dressing Parameters in Fine Cylindrical Grinding

The optimum conditions for dressing grinding wheels determined and recommended in the literature are valid only for particular types and tools of dressing and grinding. In this paper, an attempt has been made to optimize the dressing process parameters in fine cylindrical grinding. To define the optimum values of the dressing process variables (radial feed rate of diamond roller dresser frd , dressing speed ratio qd , dress-out time td , diamond roller dresser grit size/grinding wheel grit size ratio qg , type of synthetic diamonds and direction of dressing), a multi-objective optimization has been performed based on a genetic algorithm. In the capacity of the optimization parameter, a generalized geometric-mean utility function has been chosen, which appears to be a complex indicator characterizing the roughness and accuracy of the ground surface, the grinding wheel lifetime and the manufacturing net costs of the grinding operation. The optimization problem has been solved in the following sequence: 1) a model of the generalized utility function has been created reflecting the complex effect of the dressing system parameters; 2) the optimum conditions of uni-directional and counter-directional dressing of aluminium oxide grinding wheels by experimental diamond roller dressers of synthetic diamonds of АС32 and АС80 types and different grit size at which the generalized utility function has a maximum have been determined; 3) a Pareto optimum solution has been found (frd = 0.2 mm/min; qd = 0.8; td = 4.65 s; qg = 2.56), which guarantees the best combination between the roughness and the deviation from cylindricity of the ground surface, the grinding wheel lifetime and the manufacturing net costs of the grinding operation.

Multi-Objective Optimization of the Dressing Parameters in Fine Cylindrical Grinding

The optimum conditions of dressing grinding wheels determined and recommended in the literature are valid only for particular types and tools of dressing and grinding. In this paper an attempt has been made to optimize the dressing system parameters in fine cylindrical grinding. To define the optimum values of dressing process variables (radial in-feed of diamond roller dresser , dressing speed ratio , dress-out time , diamond roller dresser grit size/grinding wheel grit size ratio , type of synthetic diamonds and direction of dressing) a multi-objective optimization has been performed based on genetic algorithm. In the capacity of optimization parameter a generalized geometric-mean utility function has been chosen which appears to be a complex indicator characterizing the roughness and accuracy of the ground surface, grinding wheel lifetime and the manufacturing net costs of grinding operation. The optimization problem has been solved in the following sequence: 1) a model of the generalized utility function has been created reflecting the complex effect of dressing system parameters; 2) the optimum conditions of uni-directional and counter-directional dressing of aluminium oxide grinding wheels by experimental diamond roller dressers of synthetic diamonds of АС32 and АС80 types and different grit size have been determined at which the generalized utility function has a maximum; 3) Pareto optimum solution has been found (frd=0.2 mm/min; qd=0.8; td=4.65 s; qg=2.56), which guarantees the best combination between roughness and deviation from cylindricity of the ground surface, grinding wheel lifetime and the manufacturing net costs of grinding operation.

Surface Integrity of Quartz Glass Induced by Ultra-precision Grinding

In order to achieve high efficiency and low damage grinding for quartz glass, surface and subsurface qualities of ground quartz glasses using diamond wheels of various grit sizes are systematically investigated, and a mathematic relationship between the surface roughness and the subsurface damage depth is established. Grinding performance and surface integrity of quartz glass under diamond grinding using grit size of 400#, 1 500 #, 2 000# and 5 000#, respectively, are characterized in terms of surface topography, surface roughness and subsurface defect depth. The material removal mode of quartz glass for such diamond wheels is presented as well. The mechanism of surface morphology and subsurface microcrack produced in brittle removal mode is analyzed using indentation fracture mechanics, and the relationship between roughness value PV and subsurface damage depth SSD is established. The experiment results showed that with the decrease in wheel grit size, the quality of defects including pits, microcracks and deep scratches generated on the surface decreased, resulting in the decreased surface roughness and subsurface damage depth from Ra 274.0 nm, PV 5.35 μm and SSD 5.73 μm for 400# wheel to Ra 1.4 nm, PV 0.02 μm and SSD 0.004 μm for 5 000# wheel. The dominant removal mode in grinding quartz glass for 400# and 1 500# wheel is brittle fracture, that for 2 000# wheel included both brittle fracture and ductile cutting but ductile removal is more prevalent, and that for 5 000# wheel is ductile cutting removal. In the brittle mode grinding process, the relationship between subsurface roughness value PV and subsurface damage depth SSD is in accord with the formula SSD=(0.627~1.356) PV.

Modelling and multi-objective optimisation of EDDG process using hybrid ANN-GA approach

It has been found that wheel wear rate (WWR) and surface finish is adversely affected in order to improve the material removal rate (MRR) in electrical discharge diamond grinding (EDDG) process. Therefore, simultaneous optimisation of above three responses is always desired. This research paper presents the modelling and multi-objective optimisation of EDDG using AI-based hybrid ANN-GA approach. The effect of wheel grit size has also been considered along with electrical parameters such as peak current, pulse-on time and pulse-off time. The significant control parameters for different responses have been found and effect of their variation has been discussed. The developed ANN models for different responses have been found reliable with negligible prediction errors. The optimisation results show considerable improvement of 97% in MRR with marginal increase in WWR and surface roughness.

Optimization of the dressing parameters in cylindrical grinding based on a generalized utility function

The existing studies, concerning the dressing process, focus on the major influence of the dressing conditions on the grinding response variables. However, the choice of the dressing conditions is often made, based on the experience of the qualified staff or using data from reference books. The optimal dressing parameters, which are only valid for the particular methods and dressing and grinding conditions, are also used. The paper presents a methodology for optimization of the dressing parameters in cylindrical grinding. The generalized utility function has been chosen as an optimization parameter. It is a complex indicator determining the economic, dynamic and manufacturing characteristics of the grinding process. The developed methodology is implemented for the dressing of aluminium oxide grinding wheels by using experimental diamond roller dressers with different grit sizes made of medium- and high-strength synthetic diamonds type ??32 and ??80. To solve the optimization problem, a model of the generalized utility function is created which reflects the complex impact of dressing parameters. The model is built based on the results from the conducted complex study and modeling of the grinding wheel lifetime, cutting ability, production rate and cutting forces during grinding. They are closely related to the dressing conditions (dressing speed ratio, radial in-feed of the diamond roller dresser and dress-out time), the diamond roller dresser grit size/grinding wheel grit size ratio, the type of synthetic diamonds and the direction of dressing. Some dressing parameters are determined for which the generalized utility function has a maximum and which guarantee an optimum combination of the following: the lifetime and cutting ability of the abrasive wheels, the tangential cutting force magnitude and the production rate of the grinding process. The results obtained prove the possibility of control and optimization of grinding by selecting particular dressing parameters.

Grinding Force Research on Nanostructured Ceramic Coatings

In diamond wheel precision grinding process, the grinding force of nanoceramic coating materials can be divided into single grain grinding force and wheel unit area grinding force, this paper studied the two grinding force, results showed that, with the increase of grinding depth, grinding wheel per unit area grinding force and single grain grinding force increased. The two kinds of grinding force increased also with the increase of workpiece feeding speed, the normal grinding force and the tangential grinding force decreased with grinding wheel speed increase. grinding parameters, as diamond wheel grit size and binder type, effected also on the grinding force.

Edge chipping of silicon wafers in diamond grinding

Although diamond grinding is the most commonly used machining technique in silicon wafer thinning, it often induces edge chipping which leads to wafer breakage. This study investigates edge chipping of silicon wafer in diamond grinding. The study correlates edge chipping with the crystallographic orientation and thickness of a silicon wafer, as well as grinding process conditions, such as wheel grit size, grinding mode and feed rate. It identifies edge chipping in terms of critical thickness, geometry and dimensions. The study discusses the mechanisms of edge chipping based on machining mechanics and energy theories. Conclusions are drawn to summarize the study.

High-Efficiency and Precision Grinding Technology of HIPSN All-Ceramic Bearing Race

This paper deals with the development of a high-efficiency and precision grinding technology for producing HIPSN ceramic bearing races. A new high-speed CNC grinding machine has been developed, which is equipped with a high-speed ceramic spindle with a built-in motor. Extensive experiments have been performed with this new machine to investigate the influence of various process parameters such as wheel speed, work speed, depth of cut, and wheel grit size on material removal rate, surface finish, grinding forces, and so on. The results of these investigations are presented in this paper. With the application of this technology, a low cost production of ceramic bearings race was realized with the most optimized process parameter.

Machining Cracks in Finished Ceramics

Grinding may create flaws that control strength and limit the performance of finished ceramics. Machining cracks sometimes have been difficult or impossible to find especially in toughened ceramics with interlocking grain microstructures that create rough fracture surfaces. Our fractographic examinations show that machining damage leaves telltale markings on fracture surfaces that may be easily detected using common fractographic techniques. A comprehensive study with over 400 ground rods and rectangular bars was conducted on several commercial silicon nitrides to study the effects of various machining conditions. Similarities and differences in behavior were observed. A paradoxical finding was that tougher silicon nitrides developed deeper grinding cracks. Machining crack size and shape strongly depended on the grinding wheel grit size.

ON THE NATURE OF MACHINING CRACKS IN GROUND CERAMICS: PART I: SRBSN STRENGTHS AND FRACTOGRAPHIC ANALYSIS

ABSTRACT Machining cracks in ground sintered reaction-bonded silicon nitride (SRBSN) rods and bars were analyzed by fractographic techniques. Grinding flaw sizes were as small as 12 µm and as large as 80 µm and correlated strongly with grinding direction and wheel grit size. Some grinding treatments had no deleterious effect on strength since the machining cracks were very small and fracture occurred from the material's inherent flaws. The telltale signs of machining damage may be detected with conventional low power optical microscopy using simple fractographic techniques. The telltale signs are summarized in a new series of schematic drawings which will aid pattern recognition for engineers and fractographers.

ON THE NATURE OF MACHINING CRACKS IN GROUND CERAMICS: PART II, COMPARISON TO OTHER SILICON NITRIDES AND DAMAGE MAPS

ABSTRACT The size and severity of grinding machining cracks in a sintered reaction bonded silicon nitride are compared to data for other silicon nitrides. Crack sizes follow a similar trend with grinding wheel grit size despite differences in microstructures, strengths, and fracture toughnesses. Silicon nitrides with enhanced fracture toughness actually develop deeper machining cracks than in less tough silicon nitrides. Machining damage maps for silicon nitride are presented.

Loose abrasive truing and dressing of resin bond diamond cup wheels for grinding fibre optic connectors

A loose abrasive lapping technology was developed for truing and dressing ultrafine diamond cup wheels for grinding spherical end faces of fibre optic connectors. The relative densities of exposed grits and grit pull-outs measured from wheel surfaces prepared using the loose abrasive lapping and the bonded abrasive dressing were compared. It was found that the lapping method with loose abrasives produced wheel surfaces with more exposed grits and less grit pull-outs, especially for finer grit size wheels. For dressing ultrafine grit size wheels, the particle size of the lapping paste should be smaller than the wheel grit size to achieve a better result. It is also found that the wheels dressed using the lapping method demonstrate an excellent grinding performance.

The optimisation of the grinding of silicon carbide with diamond wheels using genetic algorithms

Modelling and optimisation are necessary for the control of any process to achieve improved product quality, high productivity and low cost. The grinding of silicon carbide is difficult because of its low fracture toughness, making it very sensitive to cracking. The efficient grinding of high performance ceramics involves the selection of operating parameters to maximise the MRR while maintaining the required surface finish and limiting surface damage. In the present work, experimental studies have been carried out to obtain optimum conditions for silicon carbide grinding. The effect of wheel grit size and grinding parameters such as wheel depth of cut and work feed rate on the surface roughness and damage are investigated. The significance of these parameters, on the surface roughness and the number of flaws, has been established using the analysis of variance. Mathematical models have also been developed for estimating the surface roughness and the number of flaws on the basis of experimental results. The optimisation of silicon carbide grinding has been carried out using genetic algorithms to obtain a maximum MRR with reference to surface finish and damage.

Grinding of nanostructural ceramic coatings: damage evaluation

This paper investigates the damage, mainly surface and subsurface cracks, in ground n-Al 2O 3/13TiO 2 and n-WC/12Co coatings. Surface cracks are formed under some special conditions. The presence and formation of the surface cracks are studied. Subsurface damage, especially cracks, of the ground components greatly influences their performance and life in service. The effects of the grinding conditions such as material removal rate, wheel grit size and bond materials on the subsurface damage, especially subsurface cracks, are investigated. The difference of material properties of these two coatings also influences the subsurface cracks. Different from bulk samples, large quantities of defects inherited from the thermal spray process play a significant role in the initiation and development of the cracks, present the crack configurations more complex than the typically reported system of median and lateral cracks observed in ground bulk ceramics. This complexity is analyzed.

Grinding of nanostructured ceramic coatings: surface observations and material removal mechanisms

Surface grinding of thermally sprayed nanostructured WC/12Co and Al 2O 3/13TiO 2 ( n-WC/12Co and n-Al 2O 3/13TiO 2) coatings has been undertaken with diamond wheels and under various grinding conditions. This paper investigates the effects of the grinding parameters such as depth of cut, feedrate, wheel grit size and bond materials on grinding forces, surface finish and surface topography. Different from their consolidated counterparts, the coatings have large quantities of defects inherited from thermal spray process, which greatly influence the grinding process and ground coatings. The competing phenomenon between the effects on surface finish from both the thermal spray process and the grinding process is studied. Different surface topographies are observed and their relationship with grinding conditions and material properties is investigated. Furthermore, the material removal mechanisms in grinding are explored. The effects of grinding parameters, material properties and the defects from thermal spray process on material removal mechanisms are discussed.

The Effect of Grinding Conditions on Lead Zirconate Titanate Machinability

In many of the existing and newly emerging applications for ferroelectrics there is a need to machine them to high precision, with control over the surface and near surface properties. This is particularly the case regarding microdevices. With such devices, cracking and ferroelastic domain reorientation can result in significant degradation in device performance due to grain pullout, strength degradation and depoling of the near surface region. It is vital that the parameters controlling machinability are determined and their effects characterised. From such information, optimum machining conditions may then be selected. The effects of fixed abrasive dicing conditions have been studied in four lead zirconate titanate compositions suitable for piezoelectric actuator applications. The severity of brittle surface damage has been investigated by image analysis. The thicknesses of the depoled regions have been measured by their effects on the piezoelectric coupling factors of array elements of various widths. It has been established that machinability is particularly sensitive to wheel grit size, feed rate and material composition.

Evaluation of surface and sub-surface cracks of ground ceramic

The grinding of ceramics using diamond grinding wheels initiates a system of surface and sub-surface cracks on the ground specimens. These surface and sub-surface cracks were investigated in this research. While surface cracks are visible and can be monitored easily with any of several techniques, sub-surface cracks are difficult to detect. This research investigates both types of cracks, using acoustic emission, three-dimensional topography and scanning electron microscopy. The research links the existence of surface and sub-surface cracks to different parameters such as the grinding wheel grit size, the wheel bond hardness, the depth of cut, the machine speed and the table feed. These conditions are believed to be responsible not only for the creation of these cracks, but also for the subsequent behavior of the cracks, i.e. the amount of damage that they can create. It seems from this investigation that control over these cracks is possible by adjusting the above-mentioned parameters.

Grinding induced subsurface cracks in silicon wafers

Silicon wafers are used for production of most microchips. Various processes are needed to transfer a silicon crystal ingot into wafers. To ensure high surface quality, the damage layer generated by each of the machining processes (such as lapping and grinding) has to be removed by its subsequent processes. Therefore it is essential to assess the subsurface damage for each machining process. This paper presents the observation of subsurface cracks in silicon wafers machined by surface grinding process. Based on cross-sectional microscopy methods, several crack configurations are identified. Samples taken from different locations on the wafers are examined to investigate the effects of sample location on crack depth. The effects of grinding parameters such as feedrate and wheel rotational speed on the depth of subsurface crack have been studied by a set of factorial design experiments. Furthermore, the relation between the depth of subsurface crack and the wheel grit size is experimentally determined.

Effect of Grinding Parameters on Surface Finish of Ground Ceramics

Experimental research has been conducted into the effect of grinding parameters on surface finish of ground hot pressed silicon nitride. Wheel grit size and machine parameters of wheel depth of cut and workspeed in surface grinding have been investigated. The relationships between surface finish and the grinding parameters of grit size, grit depth of cut, surface scallop height, chip cross-sectional area, and theoretical cutting edge spacing are explored. Two unique relationships appear to exist between surface finish and chip cross-sectional area; one below chip cross-sectional area of 0.1 μm2 and another above this value. The relationship between surface finish and theoretical cutting edge spacing shows the best fit for all test data.