Dynamic Analysis Of The Motorized Spindle With Externally Pressurized Air Bearings

With the development of the manufacture technology of the integrated circuits, the diameter of the silicon wafer has gradually increased to improve throughput and reduce cost. Generally, larger wafer diameters require thicker silicon to withstand wafer manufacturing. However, the limitations of the package size for the integrated circuit require the reduction of the chip thickness. At the international level, the wafer grinders are available in the wafer diameter of 300 mm. But in domestic, the key grinding technologies of silicon wafers with large diameter have not been mastered so far. One of the main reasons is that the dynamic design methods of the wafer grinding technology haven’t been developed. To solve this problem, this paper investigates the dynamic design method of motorized spindles with aerostatic bearings on the background of the grinding technologies of 300mm silicon wafers.The main research contents and conclusions of this paper are as follows:(1) Base on the compressible air lubrication theories, the static and dynamic Reynolds equations for journal bearings and thrust bearings are deduced by the linear perturbation method considering the translational and tilting motion of the rotor; the computation methods of the static and dynamic characteristics of aerostatic bearings are deduced by the finite difference method and the Newton iteration method, which lay the foundation of the dynamic analysis of the motorized spindle.(2) Considering the translational motion in the x, y and z directions and the tilting motion around the x and y axises, the dynamic model of the rotor-bearing system with five degrees of freedom is developed based on the rigid-body dynamics. The analysis methods of the unbalance response, the force response under the grinding forces and the stability of the rotor system are deduced in this paper, and the dynamic characteristics of the spindle are studied under the design conditions.(3) The experimental equipments for testing the axial and radial static stiffness of the motorized spindle are developed based on the spring-loaded method, and the experimental equipments for testing the rotary errors of the spindle are developed with the spindle error analyzer.(4) The results show that the axial and radial static stiffness of the grinding spindle are 520N/μm and 122N/μm respectively, which are consistent with the test results of 500N/μm and 100N/μm, and the axial static stiffness of the rotary table is 1000N/μm, which is consistent with the test result of 950N/μm.The dynamic analysis model for the motorized spindle with aerostatic bearings is established and verified by the experimental results obtained by the experimental equipment presented in this paper; the dynamic design methods of the motorized spindle for grinding 300mm silicon wafers are proposed systematically. This research provideds a credible basis for the domestic production of the grinder of 300mm silicon wafers.