Out of control, the everyday fab and quality shorthand for an SPC signal, as in a lot that went OOC or a tool with three OOCs this week. An OOC says the process changed, not that product is bad; parts can be OOC while still inside specification. Most fabs log every OOC with a reason code and track OOC rates per chart, since a chart that never fires and a chart that fires daily both point to bad limits.
Two OOCs on the CVD thickness chart overnight, both on chamber B. Chamber's down until the monitor wafer passes.
Also heard as
- out of control
- OOC event
- SPC violation
Do not mix it up with
- OOS: OOS means a result fell outside the specification limits; OOC means the process moved outside its own statistical behavior.
Related terms
OOS
Out of specification: a measured result outside the spec limits, meaning the product itself is nonconforming.
OCAP
Out-of-control action plan: the scripted checklist that tells operators exactly what to do when an SPC chart fires.
Western Electric rules
Standard set of run rules that flag nonrandom patterns on a control chart, not just single points past the limits.
Special cause
Specific, identifiable source of variation that is not part of the process's normal behavior and shows up as a chart signal.