Design,Preparation And Processing Mechanism Research Of Patterned Gel Lapping Plate For Sapphire

Sapphire（α-Al₂O₃）has become the main substrate material for LED wafers because of its excellent physical and chemical properties.The surface quality of sapphire substrate is closely related to the quality of LED epitaxial layer,which has a decisive influence on the performance of LED devices.Therefore,it has important significance to improve the quality of LED wafer and promote the development of LED industry to achieve high efficiency and precision machining of sapphire substrate.However,sapphire is a typical difficulty processing material because of its high hardness,high brittleness and stable chemical properties.In the process of sapphire substrate planarization,the existing free abrasive grinding has the problems of low efficiency,high pollution and high cost,while the fixed abrasive grinding has the problems of fast abrasive wear and easy to produce scratches.Semi-fixed abrasive grinding is combined with the advantages of the tow former,but because of the flexibility of the grinding plate made of sapphire substrate surface shape accuracy is hard to control.In view of the problems in the existing sapphire substrate lapping tools,a new grinding tool with resin as the main structural support and soft gel containing diamond abrasive particles as the grinding body was proposed.The main work and conclusions about this idea in this paper are as follows:（1）From the point of view of kinematics,the paper analyzes the relative motion relationship between the abrasive particles and the workpiece in the process of eccentric single-sided grinding,establishes the model of the abrasive motion track,and puts forward the evaluation method of the uniformity of the abrasive trajectory.establishes the movement trajectory equation of grinding grains and the evaluation method of the uniformity of grinding grains,and analyzes the main factors affecting the uniformity of grinding grains and their influencing rules based on the movement trajectory model of grinding grains.The pattern,size,arrangement and the proportion of the grinding block in the surface area of the lapping plate have great influence on the uniformity of the abrasive track.Therefore,a more uniform lapping surface can be obtained and the lapping quality can be improved by choosing a reasonable pattern and parameters to design the lapping plate according to the movement model of the abrasive particles.（2）Aiming at the structure of the new lapping plate,the force analysis of the single structural unit and the whole lapping plate is carried out respectively.The influence of the grinding pressure and the proportion of the gel grinding block on the deformation of the lapping plate,the stress of the gel abrasive body and the stress of the resin support are studied.As the same as the common lapping plate,the deformation of lapping plate increases with the increase of lapping pressure.However,the resin support in the new structure lapping plate bears the main pressure.As the proportion of gel area increases,the proportion of resin support decreases,and the deformation of the millstones increases,and the grinding pressure of the gel grinder increases as well under the same pressure.At the same time,in the grinding process,a single structural unit forms a local closed container,which has a local pressurization effect and is conducive to improving the grinding efficiency.Therefore,the reasonable design of the structure of this new type of lapping plate not only improves the supporting capacity of the lapping plate,but also improves the processing efficiency of semi fixed abrasive lapping.（3）Based on the theoretical analysis of the movement trajectory uniformity of abrasive particles and the force on the lapping plate,the structure of the lapping plate is optimized and a new type of structure lapping plate is prepared according to the specifications of the lapping machine.The machining effect of the new structure lapping plate was evaluated by the experiments of single side and double sides lapping.In the process of single-sided grinding,a more uniform grinding surface can be obtained,the surface roughness fluctuation is small,the substrate surface is uniform,and the surface quality is good.In the process of double-sided grinding,high material removal rate and low surface roughness can be obtained,MRR can reach 0.27-0.35 μm / min,Ra can reach 200 nm,surface quality is better,surface accuracy including bow,warp and TTV are greatly improved,which proves that the new lapping plate has good grinding effect.At the same time,the process of processing sapphire substrate with a new type of lapping plate is analyzed,and the lapping mechanism is revealed.（4）By analyzing the grinding process,the interaction model between diamond abrasive grains and sapphire substrate in the gel abrasive body was established,and the mechanism of concession of abrasive grains in the grinding process was revealed.The finite element software（SPH）was used to simulate the retreat of diamond grains with different shapes in the bond and the cut in depth of the work-piece.Because of the high elasticity of the gel binder,the diamond grain will produce obvious concession when the force is large,which makes the abrasive particles less applying force on the surface of the work-piece.As the applying force is lower than the critical point of brittle plasticity of sapphire scratch,the plastic removal of material can be achieved during the lapping process of sapphire substrate.Through theoretical analysis and finite element simulation,the material removal mechanism of the new lapping plate lapping sapphire substrate is further revealed.The work of this paper and the related conclusions have guiding significance for the realization of high quality and high efficiency lapping of sapphire substrate.