The Research Of Precision Grinding And Chemical Mechanical Polishing On Sapphire

Sapphire that is mainly composed ofα-Al₂O₃ has high hardness,high strength,high optical transmittance,high temperature resistant,sand,rain,salt fog corrosion resistance and other excellent performance,widely used in national defense,military industry,microelectronics and optoelectronics,and other fields.For example,several important applications of sapphire include infrared window materials for military aircraft,submarines,ships,missiles and other high-performance weapons,substrate materials for gallium nitride based LED,high-power lasers,screensavers for smart phones and mobile wearable devices.High performance equipment puts forward harsh requirements on sapphire processing quality.Generally,the flatness and roughness of sapphire are required to reach nanometer level and sub-nanometer level,which have reached the limit of traditional processing and posed challenges to ultra-precision processing.The processing of sapphire spherical hood is only in the stage of coarse grinding at present.In this paper,a certain type of sapphire fairing is taken as the research object.The"Scooping method"is based on forming grinding.The workpiece is processed on a five-axis CNC milling machine made in Germany Satisloh.Before processing,parameters such as the size and height of the grinding wheel need to be input into the machine system.The center of the grinding wheel and the center of the work piece should be coexisted,and the swing termination angle of the table should be 83°-85°.Grinding method is the combination of diamond ball head grinding wheel and cup grinding wheel with different particle size.Design the grinding tool track,realizing the automation of the whole machining process.In order to ensure the reliability of fashion clamp for reverse grinding,a set of process equipment is designed.The surface roughness,dimension precision and surface profile of workpiece were measured by using Taylor roughness instrument and coordinate measuring instrument.The surface roughness of the workpiece is less than 1μm.No edge breakage,breakage,collapse and other processing defects on the surface of the workpiece.At present,the strong acid,strong alkali,additive and other chemical components in sapphire polishing liquid pose potential harm to human body and environment.Heavy metal ions are easily introduced into the substrate production process,which leads to device life decline or even failure.Chemical mechanical polishing（CMP）technology is now the most widely used ultra-precision machining technology.Polishing fluid is one of the most important factors affecting CMP processing.The use of environmentally friendly polishing liquid is becoming a trend.In this paper,the effects of abrasive types,particle size,pH regulator and surfactant in polishing fluid on the polishing effect were studied.It was found that the workpiece polished by silica sol with particle size of 80 nm is of the best quality.Choosing organic alkali 2-amino-2-methyl-1-propanol without alkali metal ion can avoid introducing metal ions in polishing process.Organic alkali has the function of complexing metal ions.The effects of different kinds of surfactants on the dispersion stability of abrasive were studied.The mechanism of surfactant action was proposed.The effects of process parameters such as pressure and rotation speed on the polishing effect were studied.When the pressure was 34.5 kpa and the rotation speed was 75 rpm,the polishing effect was the best.In this paper,an environment-friendly sapphire polishing slurry is developed,whose components are non-toxic and pollution-free.After polishing,the surface roughness of the workpiece reaches 0.449 nm.The ultra-smooth and low-lossless processing surface is obtained.