Applied Mechanics and Materials Vol. 289

Abstract: Megasonic cleaning has been one of the most successful techniques for nanoparticle cleaning in semiconductor industry. However, the megasonic energy often causes a pattern collapse and some damage to very small structure. In this study, the distribution of sonic pressure in a wet cleaning bath with different arrangement of megasonic transducers is simulated. Megasonic wave transmits directional and will be disturbed. Thus the wafer surfaces should be arranged parallel to the sound wave direction of propagation. Convergence gain in the whole cleaning space is limited but results in great variance in local areas. Thus the wafer moving, rotating and oscillating is necessary.

Abstract: A control system of double closed-loop for two-phase hybrid stepper motor which includes speed closed-loop and current closed-loop is established on the basis of fuzzy-PID control algorithm, space vector pulse width modulation (SVPWM) method, space vector conversion and mathematical modeling of stepper motor. In the control system, the stepper motor model is established according to the mathematic model; the current and speed of stepper motor are controlled in feedback by the adopting fuzzy-PID control algorithm; the space vector conversion is carried out in the current/voltage conversion section, and the space vector pulse width modulation method is used to produce pwm wave. The performance of the doubled closed-loop control system for stepper motor is analyzed by the powerful modeling and simulation function of MATLAB/Simulink. The simulation results show that the control system has favorable control performance and dynamics characteristics.

Abstract: The traditional failure mode, effect, and criticality analysis (FMECA) uses risk priority number (RPN) to evaluate the risk level of a failure mode. The RPN index is calculated by multiplication of severity, occurrence and detection factors. The most critically debated disadvantage of this approach is that various combinations of these three factors may produce an identical value of RPN. This paper reviews the drawbacks in traditional FMECA and proposes a new approach to overcome these shortcomings. The proposed approach evaluates risk of failure mode by encouragement-variable-weighted analytic hierarchy process (EVW-AHP) that can prioritize failure modes even if two or more failure modes have same RPN. An example is provided to show the potential applications of the proposed approach and the detailed computational process is presented. The results based on the case study show the proposed new methodology solves the limitations of traditional FMECA approach and is feasible.