Short-Term Capability

Short-term capability is the estimate of process potential over a limited, controlled time window with minimal drift influence - it is useful for machine acceptance and rapid diagnostics, but should not be mistaken for lifetime process behavior.

What Is Short-term capability?

• Definition: Capability computed from within-subgroup variation over closely timed runs.
• Common Metrics: Cp and Cpk based on short-window sigma estimates.
• Data Characteristics: Back-to-back samples with stable settings, often from one tool state.
• Limitation: Does not fully include long-term shifts from wear, environment, or operator changes.

Why Short-term capability Matters

• Commissioning Use: Provides rapid evidence that equipment can achieve required precision under controlled conditions.
• Debug Speed: Helps isolate intrinsic process noise before long-term drift confounds analysis.
• Benchmarking: Useful baseline for comparing tools or recipe alternatives.
• Control Design: Short-term sigma informs initial control-limit and guardband setup.
• Gap Diagnosis: Comparing short-term and long-term indices reveals hidden stability problems.

How It Is Used in Practice

• Controlled Sampling: Collect consecutive production or qualification runs under fixed conditions.
• Index Analysis: Compute Cp and Cpk with clear subgroup logic and measurement-system validation.
• Follow-On Check: Pair with long-term Ppk analysis before making release-level capability claims.

Short-term capability is an important but partial quality metric - it shows what the process can do in a sprint, not necessarily what it will do over a season.