Research On The Mechanism Of Double-sided Planetary Grinding On Sapphire Substrate

Due to its excellent chemical stability,high dielectric coefficient,high thermal conductivity and moderate price,sapphire（α-Al₂O₃）was selected for 90%of light emitting diode（LED）substrate materials.However,it was a difficult-to-machine material with Mohs hardness of grade 9.As an intermediate link in the LED industry,substrate processing would directly affect the subsequent chip packaging,and was a key link in the entire LED industry.The double-sided lapping process,which was used to reduce the substrate thickness by 70%,had a crucial impact on the overall process.At present,free abrasive was used for sapphire substrate lapping,which had a series of problems such as low processing efficiency,uncontrollable surface precision of the substrate,and difficult recovery of waste liquid and so on.In this paper,the ceramic bond diamond grinding wheel was introduced into the double-sided lapping process.According to analysis of its machining mechanism,it can be used to guide its process optimization,so as to realize the efficient precision grinding of the substrate.The precision model of substrate surface was established by kinematics analysis.The results showed that the model could predict the uniformity of substrate surface quality after machining.The smaller trajectory distribution uniformity coefficient corresponded to the substrate surface with higher surface quality.Proper rotation speed of grinding wheel,short system period and proper position of substrate on the grinding wheel were beneficial to obtain better surface uniformity.According to the study of abrasive particle distribution,a material removal rate model based on the track length was established,which could accurately predict the material removal rate before processing.The simulation results showed that the rotation speed of grinding wheel and grinding pressure had a great influence on the Material Removal Rate（MRR）.Systematic experimental was carried out,and the surface quality and subsurface damage of the substrates ground by two modes of lapping were compared.Double-sided planetary grinding could use larger particle size of abrasive to obtain even better surface quality than free abrasive lapping,and the MRR could reach 2³times than that of free abrasive lapping.The dent depth and width of the substrate surface was smaller,and the largest surface crack depth was smaller.Double-sided planetary grinding experiments were carried out on four commonly used crystal planes.By comparing the differences of the difficulty degree of the material removal,surface quality and material removal mode between four crystal planes,the influence of material properties on double-sided planetary grinding was analyzed,and the removal mechanism of four planes was revealed.The mechanical properties of the substrate dominated the material removal,and the atomic arrangement difference on the crystal plane was the dominant factor that affected the material removal mode.The research results in this paper had clarified the mechanism of double-sided planetary grinding of sapphire substrate,and had practical guiding significance for realizing green,efficient and precise double-sided lapping of sapphire substrate.