Research On The Double-Sides Polishing Method Of Layer Stacked Clamping Ultra-Thin Sapphire Wafer

Due to the excellent material properties of sapphire,it is widely used in the fields of national defense,aerospace,semiconductors,LED substrates and optical wafers.In the LED substrate preparation process,the sapphire substrate is generally back lapping using abrasive grain processing technology to improve its heat dissipation performance after the electrode is fabricated.The rapid growth of the LED industry places higher requirements on the quality and production capacity of sapphire wafers,whose thickness is getting thinner and thinner,reaching below 100?m.The double-sides polishing technology has the advantages of high flatness and parallelism,and high polishing efficiency.It is the preferred polishing method for the preparation of ultra-thin sapphire wafer.Most of the commercially available double-sided polishing equipment adopts the planetary type.For ultra-thin polishing,there is a problem of insufficient strength and rigidity of the planetary wheel cage,which results in ultra-thin sapphire wafers that are prone to chipping and running slice,which seriously limits the processing yield.In view of the above-mentioned problems,this dissertation proposes a double-sides machining method for ultra-thin sapphire wafer based on layer stacked clamping,which uses a layer stacked fixture to adsorb the ultra-thin sapphire wafer to make its equivalent thickening,and then realize the double-sides machining of ultra-thin sapphire wafer.The layer stacked fixture uses a limiter to clamp the wafer to limit its tangential displacement,and a special baseplate is designed to adsorb the wafer to limit the normal displacement.According to the reliability of layer stacked clamping,the mechanism of layer stacked adsorption for ultra-thin sapphire wafers was studied.Based on the fractal theory,a rough surface contact model between the workpiece and the baseplate surface was established,and the normal force adsorption model of the rough surface was constructed by combining Van der Waals force and capillary force related theories.The reliability of the model was verified through experiments.The research results show that the main force of normal adsorption is capillary force.The 2'sapphire wafer can generate a normal force greater than 1.4 N,which can ensure that the ultra-thin sapphire wafer is absorbed by the baseplate in the normal direction.Aiming at the uniformity problem of material removing in the double-sides polishing,the motion state and trajectory uniformity of the workpiece in the layer stacked clamping are studied.First,through the analysis of friction force and friction torque,two motion states of workpiece and its judgment basis are obtained.Based on the two motion states,a kinematics model of the workpiece rotation angular velocity was constructed,and the effects of the rotation speed ratio and the workpiece position parameters on the rotation angular velocity were analyzed.Combined with geometric kinematics,an evaluation model for the trajectory uniformity of the workpiece surface and the plate surface was established.The results show that under the two motion states,the workpiece position parameter has the greatest influence on the uniformity of the machining trajectory,the speed ratio between the inner gear and the outer gear is second,and the effect of the speed ratio between the inner gear and the plate is relatively little.Through theoretical analysis of the trajectory uniformity of the workpiece surface,the combination of speed and position parameters with good trajectory uniformity of the workpiece surface are obtained,and the motion state of the workpiece is determined.An experiment was conducted to investigate the influence of the reliability of the layer stacked fixture and the uniformity of the track on the workpiece surface on the surface quality of the ultra-thin sapphire wafer biplane machining.The limiting effect of the limiter on the workpiece is not only limited by its own material,but also affected by the friction coefficient of the baseplate.In this dissertation,the frictional force experiment combined with the shear strength of the limiter determined that the materials of the baseplate and the limiter were stainless steel and glass fiber board.The processing thickness of ultra-thin sapphire wafers is limited by the influence of the position piece on the clamping thickness of the workpiece.The relationship between the clamping thickness of limiter and the pressure is experimentally studied,and the failure form of limiter is determined.For the theoretical analysis of trajectory uniformity,the effect of different speed ratios on processing uniformity is verified through experiments.The results show that the theoretical analysis model can accurately reflect the uniformity of material removal on the workpiece surface.The surface quality of ultra-thin sapphire workpiece processed by layer stacked clamping method and paraffin bonding method was compared.The results showed that the surface roughness,flatness and material removal rate of the workpiece under the layer stacked clamping method were better than that of the paraffin bonding method,and the smooth surface with roughness(R_a)of 1.4 nm and flatness(PV)of 0.968?m could be obtained,which had a good prospect of engineering application.