Yield and quality control

In a control chart, which is an example that should be judged abnormal even though all points are within the control limits?

  1. APoints scattered randomly on both sides of the center line
  2. BAll points moving up and down inside the control limits
  3. CMany consecutive points on one side of the center line
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Answer: C. Many consecutive points on one side of the center line

Even within the control limits, patterns such as many consecutive points on one side of the center line (a run) or points rising or falling continuously (a trend) are unlikely to be chance and signal some change in the process. Using such rules allows abnormalities to be found before out-of-spec products appear.

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More Yield and quality control questions

  1. In the Poisson model Y = exp(−D × A), with defect density D = 0.1 /cm² and chip area A = 1 cm², approximately what is the yield?
  2. Among defects on a wafer, what are those called that actually cause electrical failure of a chip?
  3. Which chart divides data into intervals and shows the frequencies as bars to see the shape of the distribution of variation?
  4. Which process capability index is used when the process mean is offset from the center of the specification?
  5. Which type of control automatically adjusts equipment processing conditions for the next lot or wafer based on, for example, measurement results from earlier steps?