Upper control limit, the line above the centerline beyond which a single point counts as an out-of-control signal; its partner below the centerline is the LCL. On charts for ranges, counts or defect fractions the LCL often comes out negative by formula and is set to zero. A point below the LCL on a defect chart still deserves a look: either the process genuinely improved or the inspection stopped finding defects.
Particle adders hit 41 against a UCL of 35, so the tool goes down until we run a clean wafer and requal.
Also heard as
- upper control limit
Related terms
Control limits
Boundaries on a control chart computed from the process's own variation, marking how far routine noise normally reaches.
Control chart
Time-ordered plot of a process statistic with a centerline and limits that flag when the process has changed.
OOC
Out of control: shorthand for a point or chart that has violated a control limit or run rule.
Western Electric rules
Standard set of run rules that flag nonrandom patterns on a control chart, not just single points past the limits.