Research On Magneto-rheological Polishing Process Of Aluminum Nitride Ceramic By Used Of Conical Electromagnet Excitation

Aluminum nitride ceramics have outstanding thermodynamic properties and are one of the ideal materials for the manufacture of semiconductor substrates and high-density packaging substrates.It is generally required to have low surface roughness,high face accuracy,and low subsurface damage.The current main processing methods for aluminum nitride ceramics are solid abrasive processing and free abrasive processing.However,neither of these two methods can balance the requirements of polishing effect and processing efficiency.Therefore,the magnetorheological polishing method of aluminum nitride ceramics for tapered electromagnet excitation was proposed.This method uses semi-consolidated abrasive processing and enables efficient flattening of aluminum nitride ceramics.The main researches of this essay were as follows:(1)The factors,which affect the processing effect and removal efficiency of aluminum nitride ceramics,were determined by analyzing the material characteristics of aluminum nitride ceramics and the magnetorheological polishing theory.They are the performance of the magnetorheological polishing solution,the excitation effect of the excitation device,and the process parameter settings,respectively.The composition of the polishing solution was determined,and the configuration sequence was studied by combining the material properties of aluminum nitride ceramics and the performance requirements of the magnetorheological polishing solution.The experimental results show that the magnetorheological polishing solution formulated in the order of"magnetic particles-abrasive particles-additives"has the best anti-settling property and the most stable polishing effect.(2)A conical electromagnet excitation device was designed by the polygonal effect and the basic theory of electromagnetism.Maxwell software was used to optimize the taper,core position,and core length of the tapered solenoid and to analyze the excitation characteristics of the tapered solenoid.The simulation results show that.the excitation effect of the conical electromagnet is twice that of the cylindrical electromagnet under the same conditions.increasing the taper of the conical electromagnet increases the magnetic induction strength while bringing the peak strength closer to the center.Changes in core position and core length only affect the magnitude of magnetic induction and do not change the magnetic field distribution.The optimized conical electromagnet has 30.96%higher maximum magnetic induction strength,8.37%lower weight,and 6.69%cost savings compared to the pre-optimized one.(3)A magnetorheological polishing experimental platform excited by a conical electromagnet was built.Experiments on the polishing effect and removal efficiency of aluminum nitride ceramics were conducted for single factors such as excitation current,working gap,polishing disc speed,and workpiece speed.The optimal solutions obtained from the one-way analysis were input into the device for orthogonal test analysis.The experimental results show that The four process parameters influence the polishing effect and processing efficiency:excitation current>workpiece speed>polishing disc speed>working clearance.By the optimal process parameters of 9.5 A excitation current,200 r/min workpiece speed,20 r/min polishing disc speed,and 1.4mm working gap for 140 min continuous polishing,the surface roughness of aluminum nitride ceramics is only Ra 6.771 nm,and the average material removal rate up to0.62 mm~3/min,which realized the efficient flat processing of aluminum nitride ceramics.