Study On Preparation Of Soft And Hard Composite Structure Lapping Tool And Processing Of Single Crystal Sapphire Substrate

With the development of light-emitting diode（LED）,single crystal substrates have been given more attention.Sapphire,a kind of single crystal form ofα-Al₂O₃,has excellent optical,physical,and chemical properties,such as sufficient hardness,high wear resistance,and high temperature stability,which has been widely act as a substrate material used in Ga N-based LED.The performance and reliability of LED devices depend heavily on the processing quality of the substrate surface,which puts forward high requirements for its surface quality and surface shape accuracy.Fine lapping is a key process in the production of sapphire substrate,but the traditional fine lapping process has some problems,such as serious surface and subsurface damage,low surface shape accuracy and serious environmental pollution.In this paper,by obtaining the ductile domain removal of sapphire substrate,the soft and hard composite structure lapping tool is prepared,and the single crystal sapphire substrate is polished to obtain high surface quality and surface shape accuracy at the same time.The preparation method,interface effect and material removal mechanism of the lapping tool are deeply studied.The main research contents and conclusions of this paper include:The types of binder and curing scheme for preparing fine lapping tools with different mechanical properties are determined according to the performance parameters such as hardness and elastic modulus;The three-dimensional software Pro E is used to optimize the structure of transmission unit,scraper unit and balance frame,complete the construction of automatic film scraping device,and realize the requirements of reciprocating motion,adjustable speed,adjustable height and high precision for the preparation of fine lapping tools;The lapping plates with different mechanical properties were prepared by weighing,stirring and dispersing,knife setting,coating and scraping,curing and drying.The abrasive behavior of different mechanical properties of binders was studied by using theoretical analysis and numerical simulation,and the fine lapping of sapphire substrate under the process conditions of lapping plate with different mechanical properties was carried out.The results show that compared with the rigid lapping plate,the roughness and residual stress of the substrate surface are reduced by18.7%and 57.3%respectively due to the elastic concession effect of abrasive particles produced in the processing process of the flexible lapping plate,and the PV value is less than 3 nm,and there are only a few shallow scratches on the surface.Through the detection and analysis of wear debris,it is amorphous and the wear particles are in the state of ductile domain removal.At the same time,the removal efficiency of W40 alumina is 178.5%higher than that of W3 alumina,and the surface roughness is reduced by 47.3%.The flexible lapping plate enables the coarse abrasive to obtain the processing effect of fine abrasive.However,the surface shape accuracy of the substrate is 490.6%lower than that of the rigid lapping plate due to the low elastic modulus of the flexible lapping plate.Based on the idea of“overall hard,local soft”,the soft and hard composite structure lapping plate was prepared by composite pouring of hard and soft binder,and the sapphire substrate fine lapping of composite and flexible lapping plate was carried out.The contact behavior between abrasive particles and substrate surface in the process of substrate processing of composite plate is analyzed by using Abaqus simulation,contact mechanics,and other theories.It is concluded that the contact stress is mainly concentrated in the local convex part of the substrate surface under the support of hard structure,and the concave part will not contact with abrasive particles,so as to ensure its surface shape accuracy.The machining results show that while the surface roughness consistent with that of the flexible lapping plate is obtained,the surface shape accuracy is improved by 54.1%,and the fine lapping process of low damage and high surface shape accuracy of sapphire substrate is realized at the same time.