Read SPC Signals Before You React
Distinguish common-cause variation from special-cause signals in a semiconductor control chart.
A control chart is a decision rule, not a decoration. Common cause is process noise A stable process still moves. If every normal wiggle triggers a recipe change, the team adds variation instead of removing it. Special cause is a signal A point outside limits, a nonrandom run, or a pattern tied to maintenance, material, or tool state deserves investigation through the reaction plan. Semiconductor consequence Tiny process changes can affect many wafers. SPC keeps the team from tuning because one point feels uncomfortable or ignoring a pattern because every point is individually plausible. The habit Name the signal rule,…
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