Abstract:
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We consider multi-stage manufacturing processes in which downstream variables undergo changes that are caused by events in one of the upstream stages. For example, in the course of a semiconductor manufacturing process, reliability degradation observed in mid-process can be caused by early-stage events that occurred a month earlier. In the absence of a model that connects upstream and downstream variables, timeslides are often useful for both monitoring and diagnostics. A timeslide is a set of observations that is ordered in accordance with product passage time through a given stage. In this paper, we discuss methodology for detecting unfavorable changes in downstream variables and using timeslides to identify problematic stages in the manufacturing process. We illustrate the methodology using examples from semiconductor industry and supply chain management.
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