Example of Process Screening
You are interested in identifying unstable processes in a data table that contains 128 columns of process measurements. Each column contains a Spec Limits column property. If a process is stable, it is appropriate to calculate its process capability.
1. Select Help > Sample Data Folder and open Semiconductor Capability.jmp.
2. Select Cols > Column Viewer.
3. Select the Processes column group and click Show Summary.
This enables you to quickly see summary statistics for all of the process columns. If you scroll through the Summary Statistics table, some of the columns have the same value for their minimum and maximum, indicating that the column has constant entries. You do not want to include these columns in the analysis.
4. In the Summary Statistics table, deselect VPM1, VPM2, PMS1, SNM1, PNP6, VPM4, VPM6, VPM9, P1, and M1. The columns selected in the Summary Statistics table correspond to the columns selected in the data table.
Tip: To deselect the columns, press Ctrl and click the column name in the table.
5. In the data table, select Analyze > Quality and Process > Process Screening.
6. Click Process Variables. This assigns the columns that are already selected in the data table as the process variables.
Notice that the Control Chart Type is set to Indiv and MR.
7. Click OK.
Figure 8.2 Partial View of Initial Report
The Process Screening window appears, showing a table of results for each process. The table is sorted by Stability Index. This is a measure of the stability of a process, where a stable process has a stability index near 1. Higher values of the stability index indicate a less stable process. (The sorting is indicated by the caret beside Stability Index in the report.) You want to take a closer look at processes with a stability index value greater than or equal to 1.03.
8. In the report window, select processes IVP8 through IVP9.
Each of these first 10 processes has a value of 1.03 or larger in the Stability Index column.
9. Right-click the selected processes and select Show Charts for Selected.
Figure 8.3 Charts for Highest Alarm Rate Processes
You decide to take a closer look at IVP8 (row 1, column 1 in the Charts for Selected).
10. Select the first process in the Summary table, which corresponds to IVP8.
11. Right-click the selected process and select Control Charts for Selected Items.
Figure 8.4 Control Chart Builder Report for IVP8
A Control Chart Builder report appears. Because IVP8 has a Spec Limits column property, the report also includes a capability analysis.