Study On High-Acceleration/High-Precision Aerostatic Positioning Stage For IC Packing

With the fast development of semiconductor manufacturing technology, continual increase of chip integrated level and number of pins, and decrease of distance between pitches, the cost for chip packaging becomes more and more prominent, which leads it necessary to enhance efficiency, improve quality and decrease manufacturing cost by designing a new generation of packaging equipments. As a key component, the fast start/stop and high precision positioning of high-acceleration/high-precision positioning stage are the premise and guarantee for efficient packaging.In order to meet the requirements of the new generation of packaging equipments, this thesis is mainly to study and design a completely new positioning stage and its servo-control system. The stage is directly driven by high thrust-weight ratio linear motor and supported by aerostatic bearings. Through adjusting the multi-factors of the electromechanical system, the stage can be stabilized in short time after high-acceleration moving. The work of this thesis is to realize conceptual and in-depth design, simulation, experiment and comprehensive performance assessment, providing unit and prototype design methods and solutions of key technology for high- acceleration/high-precision positioning stage for packaging equipment. The main contents and achievement are as follows:Firstly, a generalized parallel aerostatic positioning stage directly driven by linear motor is designed according to the requirements of the positioning stage for packaging equipment and attained inventive patent (Authorized Number: ZL 2004 1 0017014.0). The 3-D model is built by using parameterized modeling methods of Pro/E. Through modifying the structure feature of the 3-D parts, the spatial layout of the mechanism is made appropriately to meet their assembling and manufacturing requirements. Furthermore, the designing parameters are optimized through static and dynamics analysis using the finite element software ANSYS, which makes the deformation of the efficient surfaces of aerostatic guideways less than 0.1μm under gravitation and 3μm under gravitation, air pressure and the maximum driving force of the linear motors. And the movable mass of X axis and Y axis are 8.61Kg and 7.00Kg respectively.Secondly, the influences of the geometrical parameters of aerostatic thrust bearing with pocketed orifice-type restrictor on its performance are researched by simulation analysis and experimental verification. And the rational proportion of the parameters is obtained to ensure the bearing has better load carrying capacity (LCC), high stiffness and low mass flow rate (MFR). Moreover, a simple method of predicting supersonic gas flow inside bearing is provided. In order to simplify the process of design, calculation and optimization of the bearing, the general method for aerostatic bearing design are presented. It should be noted that, with the decrease of orifice diameter, ignoring the influences of orifice length on the bearing's performance will result in rather large errors. The conclusions of the analysis are foundations for designing aerostatic guideways.Thirdly, the finite element method is presented to calculate the performance of aerostatic guideways and the relative error is given when it is used to calculate tilt stiffness. And the method is realized by using the scientific calculation software Matlab. Because larger efficient area and more orifice number will increase the difficulty and cost of manufacture, prolong the time of internal air flow through bearing and block guideway induced by dust, heat distortion and external force, based on the finite element method, the parameters: orifice diameter, number, distribution and film thickness are optimized so that they satisfy the performance requirements, which makes the efficient area and number of orifices small at the same time. The experiments show that the calculation results of the Matlab program are correct and the performance of the linear guideways stratifies the requirements of the stage. Moreover, when the ratio of the distance of orifice rows to the wide of efficient surface is 0.38, the guideways can bear the maximum moment and have the maximum tilt stiffness according to the result of calculation.Fourthly, considering the closure characteristic of current commercial motion controller, an open architecture control system is set up by using MCT8000F4 open motion controller to meet the requirements of the high- acceleration/high-precision aerostatic positioning stage on the programmability and real time ability of the controlling system. The control computer in the system is used to set motion parameters to the motion controller and draw motion curves in order to assess the performance of the stage. The control program based on the packaging motion characteristics run in the high performance processor of the controller and could meet the requirements of programmability and real time ability simultaneously.Finally, based on the structural parameters and the simple force model of the linear motor, the dynamics models of the stage is built and verified using simulation and sweep testing. Focus on the small frictional damping of the aerostatic guideways, which make the system oscillate easily, through adjusting the velocity loop parameters of the controller, the system damping is improved and the performance of the stage is enhanced accordingly. In addition, by using appropriate feedforward and poles configuration algorithms in the velocity loop, the stage can reach very high acceleration and positioning accuracy (the maximum accelerations of X and Y axis are 8.00g and 7.34g respectively when the position accuracy is±2μm), and meet the expected design objective.