Reliability

On printed circuit boards and similar, what is the phenomenon called in which, under humid conditions, metal (such as silver or copper) dissolves as ions between biased electrodes, migrates and deposits in tree-like forms, causing a short?

  1. AElectromigration
  2. BStress migration
  3. CIon migration
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Answer: C. Ion migration

In ion migration, electrode metal dissolves into ions in the presence of moisture, migrates in the electric field to the opposite electrode and deposits there in branching (dendritic) form, eventually shorting the electrodes. It differs from electromigration, in which atoms move within a metal driven by electron flow.

  • A. Electromigration is atoms moving within a metal due to current.
  • B. Stress migration is atomic movement driven by stress.
  • C. Correct. Metal ions migrate with moisture and field, causing shorts.
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More Reliability questions

  1. In high-k/metal gate nMOS transistors, what is the degradation called in which the threshold voltage shifts when positive gate voltage and high temperature are applied continuously?
  2. In leading-edge LSI design, what is the practice called of anticipating transistor degradation from BTI and HCI over the usage period and checking that timing is met even with degraded characteristics?
  3. When estimating field lifetime from temperature-humidity test results, which model is commonly used to express the effect of humidity as a power of relative humidity?
  4. For gate insulator breakdown lifetime, why must the difference between the area of test devices and the total gate area on an actual chip be considered?
  5. When electromigration in flip-chip solder bumps becomes a problem due to large currents, where are failures known to be especially likely?