Situation Virginia is an engineer at a silicon wafer company whose products are used in the semiconductor industry. She is responsible for a process that deposits a layer of material on the wafers according to customer requirements, such as resistance or thickness. The customers’ requirements vary greatly and target values for resistance can range from 1 to 100 with a tolerance of ±5% of the target. One difficulty that Virginia faces is short production runs. Most of the production runs are between one and two days. Adding to this difficulty, Virginia sometimes must alternate between runs that have a target of around 1 or 2 to those with a target of 100. Because of the extremes in the target values and the knowledge that the variability is different for the different targets, Virginia is reluctant to use process behavior charts to study the process. Available data After talking with another engineer, Virginia decides to study the process with some short-run techniques. She collects data from Reactor 11 for a period of several days. Reactor 11 is one of many such reactors used to deposit a layer of material on the silicon wafers. Her approach is to adjust the data by charting the percent deviation from the target value. The data she has collected are given in the table “Data Values for Reactor 11.” The target values for the different products are summarized in the table “Target Values.” Questions 1. If Virginia uses the percent deviation from the target value for the short runs produced on Reactor 11, what does the analysis of the data show with respect to the behavior of Reactor 11? 2. What assumption is made when using the percent deviation from target? 3. What would be a more appropriate way to analyze the data?
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