Modeling and off-line control of fluid dispensing for electronics packaging
Chen, Daniel Xiongbiao
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Fluid dispensing is a method by which fluid materials are delivered to substrates, boards or work-pieces in a controllable manner. This method has been widely used in various packaging processes in the electronics manufacturing industry. In these processes, the flow rate of fluid dispensed and the profile of fluid formed on a board are the two most important performance variables to be controlled consistently. This research presents a comprehensive study on the modeling and control of the time-pressure dispensing processes. First of all, the characterization of the rheological behaviour of fluids for electronics packaging is addressed from both time-independent and time-dependent perspectives. Under the assumption that the pressure in the dispensing syringe has reached a steady-state status, a model representative of the steady-state flow rate of fluid dispensed is developed. To represent the profile of fluid formed on a board, the spreading of fluid on a board is addressed and a solution to this problem is established. To consider the influence of time-dependent fluid behaviour in fluid dispensing, a method of applying model updating technique is developed in this study. Based on this method, an off-line control of the dispensing process is developed to improve the consistency in the flow rate of fluid dispensed, which is broken by the time-dependent fluid behaviour. Taking into account air compressibility and the fluid inertia, a model is developed to represent the dynamics of the flow rate of fluid dispensed, which shows that the dynamics is sensitive to the air volume in the syringe. Based on the model, the inconsistency in the fluid amount dispensed due to the variation of the air volume in the syringe over a dispensing process is investigated, and an off-line control is developed to alleviate the amount inconsistency. Experiments on a typical commercial dispensing system are designed and carried out to verify the effectiveness of the models and the off-line control developed in this study. It is shown that the model results have an excellent agreement with the experimental results. Also, with the introduction of the off-line control, the consistency in both the flow rate and the amount of fluid dispensed can be significantly improved.