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liliconcom

Within sigma mismatch between IMR control chart & process screening platform

Hello,

I am trying to plot control charts for various process parameters. My data is a monitoring data where I get one data point for each parameter every week. The parameter shown here is the std dev measurement from the monitor wafer. I am trying to plot these std dev. data points from multiple weeks into an IMR chart. I was trying to use JMP process screening platform to be able to short list among 100s of other parameters. The problem I am having is that when I use process screening summary, the stability index is showing as 1.21 (green). When I select the parameter and plot control chart for the selected item, the control chart shows a stability index of 3.302531.

Here are some snap shots

Process screening summary
Distributions & Process Capability
IMR control chart --> Discrepancy for within sigma seen here. My sub group size is 1 and I have locked in the control limits. There is a note on the control chart that says "Within Sigma is set to a value derived from user-defined control limits".

So what should I be doing to plot this kind of data on a control chart using process screening? I wanted to use the process performance graph as a tool to shortlist the parameters whose control charts need to be plotted vs. plotting 100s of charts everyday for the manufacturing line. I am attaching the data set behind this graph.