Reliability

Learn the basics of semiconductor reliability — the bathtub curve, electromigration and MTBF — through multiple-choice questions.

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Reliability: key points

Reliability is the ability of a product to keep functioning under specified conditions for a specified time. How the failure rate changes over time is described by the bathtub curve, made up of early-failure, random-failure and wear-out periods.

Failure mechanisms specific to semiconductors include electromigration in interconnects, time-dependent dielectric breakdown (TDDB) of gate insulators, and degradation of transistor characteristics. Accelerated tests estimate lifetimes in a short time.

All Reliability questions (50)

  1. Which correctly lists the three periods that make up the bathtub curve, showing how failure rate changes over time?
  2. Which correctly describes electromigration?
  3. Which correctly describes MTBF (mean time between failures)?
  4. In accelerated tests that raise temperature to shorten life test time, which model is often used to express the relationship between temperature and lifetime?
  5. Which correctly describes TDDB (time-dependent dielectric breakdown)?
  6. What does the failure-rate unit FIT mean?
  7. Which failures are mainly evaluated by temperature cycling tests?
  8. What is provided at an LSI's I/O pins as a countermeasure against ESD (electrostatic discharge)?
  9. Which degradation phenomenon causes the absolute value of a pMOS transistor's threshold voltage to gradually increase under sustained negative gate voltage and high temperature?
  10. Which correctly describes latch-up in CMOS circuits?
  11. Which phenomenon degrades transistor characteristics when carriers accelerated by the high electric field near the drain are injected into the gate dielectric?
  12. Which failures are mainly evaluated by temperature-humidity-bias tests (THB and HAST)?
  13. Which distribution, often used in reliability data analysis, can represent early-failure, random-failure and wear-out types depending on its shape parameter?
  14. Which phenomenon creates voids as metal atoms move due to internal stress in wiring, even without current flowing?
  15. What is the phenomenon called in which needle-like metal crystals grow from the surface of tin plating and short to an adjacent terminal?
  16. Which typical reliability test evaluates lifetime and failure rate by operating products at high temperature for a long time?
  17. For a failure mechanism with an activation energy of 0.7 eV, approximately what is the Arrhenius acceleration factor of 125 °C relative to 55 °C? (Boltzmann constant 8.6×10⁻⁵ eV/K)
  18. Which correctly describes the general approach to failure analysis?
  19. What is the common name for the phenomenon in which, at gold wire to aluminum pad bonds, intermetallic compounds and voids grow during long storage at high temperature, weakening the bond?
  20. In which environment is the rate of soft errors caused by cosmic-ray neutrons higher?
  21. Which standard is widely used as the reliability qualification standard for automotive integrated circuits?
  22. When the failure rate λ is constant, which expression gives the probability of no failure up to time t (reliability) R(t)?
  23. What is the mean time to failure (MTTF) of a part with a constant failure rate of 1×10⁻⁵ per hour?
  24. What is the reliability of a system with two parts of reliability 0.9 connected in parallel, which functions if either one works?
  25. What is the reliability of a system with two parts of reliability 0.9 connected in series, which functions only if both work?
  26. In TDDB lifetime evaluation, why are tests run at voltages higher than the actual operating voltage?
  27. For mobile devices such as smartphones, which test is especially emphasized in evaluating solder joint reliability?
  28. Which failure can occur when electromigration creates a hillock on a wire?
  29. Which reliability test condition is appropriate for statistically guaranteeing a very low failure rate?
  30. In thin gate oxides, what is the mild breakdown called in which leakage current increases in steps before insulation is completely lost?
  31. Which pair correctly names "failures in which function is suddenly and completely lost" and "failures in which characteristics gradually drift out of specification"?
  32. For typical consumer semiconductor products, which is closest to the usage period commonly assumed in reliability design?
  33. For the same kind of semiconductor, which correctly describes the reliability levels required for consumer and automotive use?
  34. Based on the rule of thumb often used for chemical reactions and degradation, that "reaction speed roughly doubles for every 10 °C rise", how does lifetime change when the operating temperature is lowered by 10 °C?
  35. What is the main purpose of collecting and analyzing information on failures of products in use in the market (field failures)?
  36. Among ESD (electrostatic discharge) test models, which pair correctly names "discharge when a charged person touches an IC pin" and "discharge when the IC itself is charged and a pin touches metal"?
  37. Which thermodynamics-based model expresses lifetime acceleration including the effects of multiple stresses such as humidity and voltage in addition to temperature?
  38. Which model expresses the fatigue life of solder joints under temperature cycling as a relationship between the temperature swing (strain magnitude) and the number of cycles?
  39. Which statistical distribution is commonly used to describe the times to failure of many wires in electromigration life tests?
  40. In automotive and similar applications, what is the summary called of which temperature, voltage and operating-time conditions a product will be exposed to over its lifetime?
  41. If 10,000 parts with a failure rate of 100 FIT are used for one year (about 8,760 hours), which is closest to the expected number of failures? (1 FIT = 1 failure per 10⁹ hours)
  42. 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?
  43. 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?
  44. 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?
  45. 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?
  46. 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?
  47. When electromigration in flip-chip solder bumps becomes a problem due to large currents, where are failures known to be especially likely?
  48. Regarding BTI degradation, part of the threshold voltage shift recovers once the stress is removed. What does this imply for evaluation?
  49. 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?
  50. 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?

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