Opening the spec, or opening up the spec, means relaxing a USL or LSL. Sometimes data justify it, showing the old limit was tighter than the function needs; sometimes it is done just to rescue yield or a capability index. Done properly it needs design engineering sign-off, correlation to end-of-line results and often customer approval. Done casually, it moves the problem downstream to the next test or to the field.
Opening the spec on step height gets Cpk over 1.33 on paper, but nobody has shown the downstream CMP can take it.
When a capability problem disappears the week after a spec change, read the change history before you congratulate anyone.
Also heard as
- opening up the spec
- spec relaxation
- spec widening
Related terms
Specification limits
Acceptance boundaries for a product characteristic set by design or customer requirements, labeled USL and LSL.
Cpk
Process capability index that accounts for centering: distance from the mean to the nearest spec limit in units of 3 sigma.
OOS
Out of specification: a measured result outside the spec limits, meaning the product itself is nonconforming.
Process capability
How well a stable process's natural spread fits inside the specification limits, usually expressed as an index.