Reliability

Which statistical distribution is commonly used to describe the times to failure of many wires in electromigration life tests?

  1. ABinomial distribution
  2. BLognormal distribution
  3. CUniform distribution
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Answer: B. Lognormal distribution

Electromigration failure times often scatter like a normal distribution when the logarithm of time is taken, so they are analyzed with a lognormal distribution. From the median and spread obtained in tests, the probability that a tiny fraction of wires fails early is estimated to set design rules for current density.

  • A. The binomial distribution counts successes and failures, not failure times.
  • B. Correct. The lognormal distribution is commonly used.
  • C. A uniform distribution cannot describe failure-time scatter.
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