Study On Surface Morphology And Crack Damage Of As-sawn Wafers In Diamond Wire Saw Slicing Sapphire Crystal

Sapphire crystals are widely used in light emitting diode(LED)substrate materials and electronic equipment window materials due to their excellent material properties.Sapphire crystal processing mainly is mainly divided into several process such as slicing,grinding,polishing and other processes.Slicing is the first processing process,which widely uses diamond wire saw.There is residual damage produced for as-sawn wafer in cutting process.The surface roughness,surface morphology and subsurface microcrack damage depth of the assawn wafers are important indicators to measure the cutting quality.The cutting quality directly determines the cost of the subsequent processing of the as-sawn wafers and the service life of the components.Studies have shown that sawing parameters and the saw wire parameters are closely related to the cutting quality.Therefore,it is very necessary to study the influence of the sawing parameters and the saw wire parameters on the surface and subsurface characteristics of the as-sawn wafers.The C-plane of sapphire crystal is the most widely used substrate material.In this paper,the influence of sawing parameters and saw wire parameters on the surface and subsurface characteristics of sapphire crystal during diamond wire saw cutting C-plane in industrial production was studied.The continuous wear of the saw wire during the sawing process leads to the sawing performance of the saw wire is different in different service stages,which poses a challenge to the study of the influence of sawing parameters on the as-sawn wafer sawing quality.Therefore,we firstly studied the evolution rule of the wear and the sawing performance of the saw wire in the whole life cycle of the diamond wire saw to determine the stable service period.On this basis,sawing experiments were carried out within the industrial production parameters of sapphire,and the effects of sawing parameters on the surface and subsurface characteristics of the as-sawn wafer were studied.The sawing models for predicting the surface roughness and subsurface microcrack damage depth(SSD)of sapphire as-sawn wafers were further established.The results of this paper can provide theoretical and experimental reference for the industrial production of diamond wire saw cutting sapphire crystal.The research work of this paper mainly includes the following contents:(1)Firstly,the evolution of abrasive wear state,saw wire diameter,saw wire wear rate,assawn wafer surface roughness and surface morphology with the increase of sawing area of saw wire during the whole service cycle of saw wire was analyzed under typical sawing parameters.The research shows that the service cycle of the saw wire can be divided into three periods:early stage,middle stage and later stage.In the middle saw wire service stage,the abrasive wear is slow,the sawing performance of the saw wire is stable,and the as-sawn wafer surface quality is high.Sawing sapphire can effectively improve the as-sawn wafers sawing quality in this stage.Furthermore,sawing experiments were carried out in the saw wire middle service stage,and the effects of sawing parameters on the as-sawn wafers surface and subsurface characteristics were studied within the industrial production parameters of sapphire crystal,which provided experimental guidance for optimizing the sawing process.(2)According to the wire sawing cutting mechanism and sapphire crystal removal mechanism,a numerical calculation model of sapphire as-sawn wafer surface roughness was established,and the validity of the model was verified by the data got from the sawing experiment.Based on this mathematical model,the mapping relationship between the sawing speed ratio Vf/Vs,the size and density of diamond abrasive fixed on the saw wire surface and the as-sawn wafer surface roughness and surface morphology was obtained.(3)Based on the stress field model of single abrasive scratching on the C-plane of sapphire,a calculation model of subsurface microcrack damage depth of sapphire as-sawn wafer was established.The model considers the material removal mode of each abrasive fixed on the saw wire surface and the median crack propagation angle under the action of abrasives.The model was used to simulate the relationship between cutting parameters and as-sawn wafer SSD and the validity of the model was verified by experimental data.The effects of speed ratio Vf/Vs and saw wire parameters on the as-sawn wafer SSD were numerically calculated using this model.