Reliability

When electromigration in flip-chip solder bumps becomes a problem due to large currents, where are failures known to be especially likely?

  1. ANear the bump-to-wiring connection, where current crowds into one point
  2. BAt the center of the bump where no current flows
  3. CIn the resin outside the package
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Answer: A. Near the bump-to-wiring connection, where current crowds into one point

In solder bumps, current density becomes locally very high at the corner of the connection where current enters the wide bump from a narrow trace (current crowding), so voids readily form there. Temperature rise from Joule heating and growth of intermetallic compounds between solder and metal also accelerate degradation.

  • A. Correct. Failures tend to occur near the connection where current crowds.
  • B. Electromigration does not occur where no current flows.
  • C. The resin does not carry current.
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More Reliability questions

  1. Regarding BTI degradation, part of the threshold voltage shift recovers once the stress is removed. What does this imply for evaluation?
  2. To evaluate susceptibility to soft errors caused by cosmic-ray neutrons, which method measures quickly by applying neutrons far more intense than in the real environment?
  3. When extrapolating TDDB test results to operating voltage, there is the E model, which expresses lifetime as an exponential of field, and the 1/E model, which uses the reciprocal of field. Which statement about their difference is correct?
  4. Which correctly lists the three periods that make up the bathtub curve, showing how failure rate changes over time?
  5. Which correctly describes electromigration?