Advanced Technology Symposium Conference Proceedings


Authors: Leandro G. Barajas
Company: Georgia Institute of Tech.
Date Published: 6/11/2002   Conference: Advanced Technology Symposium

Abstract: In this paper a control algorithm, that generates adequate machine settings for the Stencil Printing Process (SPP) in Surface Mount Technology manufacturing, is presented. The SPP is characterized by high process-noise levels, and by requiring constant solder-paste volume deposition at all times. Due to the prohibitive cost associated with extensive testing, only a limited amount of information can be used in the decision-making. The major constraint when controlling the SPP is that it is not possible to evaluate the output of the system an arbitrary number of times, since for each calculation the printing and inspection of at least one or even two new boards is required.

These difficulties are addressed by the controller proposed in this paper, which is based on an algorithm for generating a sequence of iterative values that converge to an optimum set of machine parameters for a desired solder paste volume. The merit of the control is that it minimizes the variance and the steady state error of the weighted sample mean versus the desired height, which improves the quality of the process. In addition, it considers print direction and different component types independently. Finally, this controller also automatically corrects for the process errors associated with the loss of the solder-paste working-viscosity-point, which can occur due to unscheduled stops on the line, and for incorrect specification of machine parameters given by the operator.

Keywords: Stencil printing process control, least squares, affine estimator.

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