Failure of electronic components

Electronic components have a wide range of

, mechanical shock, stress or impact, and many other causes. In semiconductor devices, problems in the device package may cause failures due to contamination, mechanical stress of the device, or open or short circuits.

Failures most commonly occur near the beginning and near the ending of the lifetime of the parts, resulting in the bathtub curve graph of failure rates. Burn-in procedures are used to detect early failures. In semiconductor devices, parasitic structures, irrelevant for normal operation, become important in the context of failures; they can be both a source and protection against failure.

Applications such as aerospace systems, life support systems, telecommunications, railway signals, and computers use great numbers of individual electronic components. Analysis of the statistical properties of failures can give guidance in designs to establish a given level of reliability. For example, power-handling ability of a resistor may be greatly derated when applied in high-altitude aircraft to obtain adequate service life. A sudden fail-open fault can cause multiple secondary failures if it is fast and the circuit contains an inductance; this causes large voltage spikes, which may exceed 500 volts. A broken metallisation on a chip may thus cause secondary overvoltage damage.^[1] Thermal runaway can cause sudden failures including melting, fire or explosions.

Packaging failures

The majority of electronic parts failures are

, especially when the thermal expansion coefficients of the materials are different. Humidity and aggressive chemicals can cause corrosion of the packaging materials and leads, potentially breaking them and damaging the inside parts, leading to electrical failure. Exceeding the allowed environmental temperature range can cause overstressing of wire bonds, thus tearing the connections loose, cracking the semiconductor dies, or causing packaging cracks. Humidity and subsequent high temperature heating may also cause cracking, as may mechanical damage or shock.

During encapsulation, bonding wires can be severed, shorted, or touch the chip die, usually at the edge. Dies can crack due to mechanical overstress or thermal shock; defects introduced during processing, like scribing, can develop into fractures. Lead frames may contain excessive material or burrs, causing shorts. Ionic contaminants like alkali metals and halogens can migrate from the packaging materials to the semiconductor dies, causing corrosion or parameter deterioration. Glass-metal seals commonly fail by forming radial cracks that originate at the pin-glass interface and permeate outwards; other causes include a weak oxide layer on the interface and poor formation of a glass meniscus around the pin.^[2]

Various gases may be present in the package cavity, either as impurities trapped during manufacturing,

Contact failures

Electrical contacts exhibit ubiquitous

significantly, leading to resistance heating and circuit failure.

Soldered joints can fail in many ways like

, in addition to the methods described above, may fail by fraying and fire damage.

Printed circuit board failures

.

Above the

Multi-layer substrates using ceramics suffer from many of the same problems.

Conductive anodic filaments (CAFs) may grow within the boards along the fibers of the composite material. Metal is introduced to a vulnerable surface typically from plating the vias, then migrates in presence of ions, moisture, and electrical potential; drilling damage and poor glass-resin bonding promotes such failures.^[6] The formation of CAFs usually begins by poor glass-resin bonding; a layer of adsorbed moisture then provides a channel through which ions and corrosion products migrate. In presence of chloride ions, the precipitated material is atacamite; its semiconductive properties lead to increased current leakage, deteriorated dielectric strength, and short circuits between traces. Absorbed glycols from flux residues aggravate the problem. The difference in thermal expansion of the fibers and the matrix weakens the bond when the board is soldered; the lead-free solders which require higher soldering temperatures increase the occurrence of CAFs. Besides this, CAFs depend on absorbed humidity; below a certain threshold, they do not occur.^[5] Delamination may occur to separate the board layers, cracking the vias and conductors to introduce pathways for corrosive contaminants and migration of conductive species.^[6]

Relay failures

Every time the contacts of an electromechanical relay or contactor are opened or closed, there is a certain amount of contact wear. An electric arc occurs between the contact points (electrodes) both during the transition from closed to open (break) or from open to closed (make). The arc caused during the contact break (break arc) is akin to arc welding, as the break arc is typically more energetic and more destructive.^[7]

The heat and current of the electrical arc across the contacts creates specific cone & crater formations from metal migration. In addition to the physical contact damage, there appears also a coating of carbon and other matter. This degradation drastically limits the overall operating life of a relay or contactor to a range of perhaps 100,000 operations, a level representing 1% or less than the mechanical life expectancy of the same device.^[8]

Semiconductor failures

Many failures result in generation of

Examples of semiconductor failures relating to semiconductor crystals include:

• Nucleation and growth of dislocations. This requires an existing defect in the crystal, as is done by radiation, and is accelerated by heat, high current density and emitted light. With LEDs, gallium arsenide and aluminium gallium arsenide are more susceptible to this than gallium arsenide phosphide and indium phosphide; gallium nitride and indium gallium nitride are insensitive to this defect.
• Accumulation of
  hot carrier injection, ionizing radiation or nominal use. With EEPROM
  cells, this is the major factor limiting the number of erase-write cycles.
• Migration of charge carriers from
  floating gates. This limits the lifetime of stored data in EEPROM
  and flash EPROM structures.
• Improper passivation. Corrosion is a significant source of delayed failures; semiconductors, metallic interconnects, and passivation glasses are all susceptible. The surface of semiconductors subjected to moisture has an oxide layer; the liberated hydrogen reacts with deeper layers of the material, yielding volatile hydrides.^[10]

Parameter failures

Vias are a common source of unwanted serial resistance on chips; defective vias show unacceptably high resistance and therefore increase propagation delays. As their resistivity drops with increasing temperature, degradation of the maximum operating frequency of the chip the other way is an indicator of such a fault. Mousebites are regions where metallization has a decreased width; such defects usually do not show during electrical testing but present a major reliability risk. Increased current density in the mousebite can aggravate electromigration problems; a large degree of voiding is needed to create a temperature-sensitive propagation delay.^[9]

Sometimes, circuit tolerances can make erratic behaviour difficult to trace; for example, a weak driver transistor, a higher series resistance and the capacitance of the gate of the subsequent transistor may be within tolerance but can significantly increase signal

Overstress-induced damage like ohmic shunts or a reduced transistor output current can increase such delays, leading to erratic behavior. As propagation delays depend heavily on supply voltage, tolerance-bound fluctuations of the latter can trigger such behavior.

Gallium arsenide monolithic microwave integrated circuits can have these failures:^[11]

• Degradation of I_DSS^[12] by gate sinking and hydrogen poisoning. This failure is the most common and easiest to detect, and is affected by reduction of the active channel of the transistor in gate sinking and depletion of the donor density in the active channel for hydrogen poisoning.
• Degradation in gate
  leakage current
  . This occurs at accelerated life tests or high temperatures and is suspected to be caused by surface-state effects.
• Degradation in
  barrier metal
  between the contacts and gallium arsenide.
• Increase in drain-to-source resistance. It is observed in high-temperature devices, and is caused by metal-semiconductor interactions, gate sinking and ohmic contact degradation.

Metallisation failures

Metallisation failures are more common and serious causes of FET transistor degradation than material processes;

Examples of such failures include:

• nonradiative recombination
  along chip edges. In all cases, electromigration can cause changes in dimensions and parameters of the transistor gates and semiconductor junctions.
• Mechanical stresses, high currents, and corrosive environments forming of
  circuit boards
  .
• Formation of silicon nodules.
  Aluminium interconnects may be silicon-doped to saturation during deposition to prevent alloy spikes. During thermal cycling, the silicon atoms may migrate and clump together forming nodules that act as voids, increasing local resistance and lowering device lifetime.^[2]
• Ohmic contact degradation between metallisation and semiconductor layers. With gallium arsenide, a layer of gold-germanium alloy (sometimes with nickel) is used to achieve low contact resistance; an ohmic contact is formed by diffusion of germanium, forming a thin, highly n-doped region under the metal facilitating the connection, leaving gold deposited over it. Gallium atoms may migrate through this layer and get scavenged by the gold above, creating a defect-rich gallium-depleted zone under the contact; gold and oxygen then migrate oppositely, resulting in increased resistance of the ohmic contact and depletion of effective doping level.^[13] Formation of intermetallic compounds also plays a role in this failure mode.

Electrical overstress

Most stress-related semiconductor failures are electrothermal in nature microscopically; locally increased temperatures can lead to immediate failure by melting or vaporising metallisation layers, melting the semiconductor or by changing structures. Diffusion and electromigration tend to be accelerated by high temperatures, shortening the lifetime of the device; damage to junctions not leading to immediate failure may manifest as altered current–voltage characteristics of the junctions. Electrical overstress failures can be classified as thermally-induced, electromigration-related and electric field-related failures; examples of such failures include:

• Kirkendall voiding. Clustered distribution of current density over the junction or current filaments lead to current crowding
  localised hot spots, which may evolve to a thermal runaway.
• Reverse bias
  . Some semiconductor devices are diode junction-based and are nominally rectifiers; however, the reverse-breakdown mode may be at a very low voltage, with a moderate reverse bias voltage causing immediate degradation and vastly accelerated failure. 5 V is a maximum reverse-bias voltage for typical LEDs, with some types having lower figures.
• Severely overloaded Zener diodes in reverse bias shorting. A sufficiently high voltage causes avalanche breakdown of the Zener junction; that and a large current being passed through the diode causes extreme localised heating, melting the junction and metallisation and forming a silicon-aluminium alloy that shorts the terminals. This is sometimes intentionally used as a method of hardwiring connections via fuses.^[14]
• SCR then may cause an overcurrent-based failure. In ICs, latchups are classified as internal (like transmission line reflections and ground bounces) or external (like signals introduced via I/O pins and cosmic rays); external latchups can be triggered by an electrostatic discharge while internal latchups cannot. Latchups can be triggered by charge carriers injected into chip substrate or another latchup; the JEDEC78 standard tests susceptibility to latchups.^[9]

Electrostatic discharge

Electrostatic discharge (ESD) is a subclass of electrical overstress and may cause immediate device failure, permanent parameter shifts and latent damage causing increased degradation rate. It has at least one of three components, localized heat generation, high current density and high electric field gradient; prolonged presence of currents of several amperes transfer energy to the device structure to cause damage. ESD in real circuits causes a

• Oxide breakdown occurring at field strengths above 6–10 MV/cm.
• Junction damage manifesting as reverse-bias leakage increases to the point of shorting.
• Metallisation and polysilicon burnout, where damage is limited to metal and
  polysilicon
  interconnects, thin film resistors and diffused resistors.
• Charge injection, where hot carriers generated by avalanche breakdown are injected into the oxide layer.

Catastrophic ESD failure modes include:

• Junction burnout, where a conductive path forms through the junction and shorts it
• Metallisation burnout, where melting or vaporizing of a part of the metal interconnect interrupts it
• Oxide punch-through, formation of a conductive path through the insulating layer between two conductors or semiconductors; the gate oxides are thinnest and therefore most sensitive. The damaged transistor shows a low-ohmic junction between gate and drain terminals.

A parametric failure only shifts the device parameters and may manifest in stress testing; sometimes, the degree of damage can lower over time. Latent ESD failure modes occur in a delayed fashion and include:

• Insulator damage by weakening of the insulator structures.
• Junction damage by lowering minority carrier lifetimes, increasing forward-bias resistance and increasing reverse-bias leakage.
• Metallisation damage by conductor weakening.

Catastrophic failures require the highest discharge voltages, are the easiest to test for and are rarest to occur. Parametric failures occur at intermediate discharge voltages and occur more often, with latent failures the most common. For each parametric failure, there are 4–10 latent ones.

circuits are more ESD-sensitive, with smaller features, lower capacitance and higher voltage-to-charge ratio. Silicon deposition of the conductive layers makes them more conductive, reducing the ballast resistance that has a protective role.

The

Current-induced failures are more common in bipolar junction devices, where Schottky and PN junctions are predominant. The high power of the discharge, above 5 kilowatts for less than a microsecond, can melt and vaporise materials. Thin-film resistors may have their value altered by a discharge path forming across them, or having part of the thin film vaporized; this can be problematic in precision applications where such values are critical.[17]

Newer CMOS

Passive element failures

Resistors

Resistors can fail open or short, alongside their value changing under environmental conditions and outside performance limits. Examples of resistor failures include:

• Manufacturing defects causing intermittent problems. For example, improperly crimped caps on carbon or metal resistors can loosen and lose contact, and the resistor-to-cap resistance can change the values of the resistor^[2]
• Surface-mount resistors delaminating where dissimilar materials join, like between the ceramic substrate and the resistive layer.^[21]
• Nichrome thin-film resistors in integrated circuits attacked by phosphorus from the passivation glass, corroding them and increasing their resistance.^[22]
• SMD resistors with silver metallization of contacts suffering open-circuit failure in a sulfur-rich environment, due to buildup of silver sulfide.^[6]
• Copper dendrites growing from Copper(II) oxide present in some materials (like the layer facilitating adhesion of metallization to a ceramic substrate) and bridging the trimming kerf slot.^[3]

Potentiometers and trimmers

Capacitors

Capacitors are characterized by their capacitance, parasitic resistance in series and parallel, breakdown voltage and dissipation factor; both parasitic parameters are often frequency- and voltage-dependent. Structurally, capacitors consist of electrodes separated by a dielectric, connecting leads, and housing; deterioration of any of these may cause parameter shifts or failure. Shorted failures and leakage due to increase of parallel parasitic resistance are the most common failure modes of capacitors, followed by open failures.^{[citation needed]} Some examples of capacitor failures include:

• Dielectric breakdown due to overvoltage or aging of the dielectric, occurring when breakdown voltage falls below operating voltage. Some types of capacitors "self-heal", as internal arcing vaporizes parts of the electrodes around the failed spot. Others form a conductive pathway through the dielectric, leading to shorting or partial loss of dielectric resistance.^[2]
• Electrode materials migrating across the dielectric, forming conductive paths.[2]
• Leads separated from the capacitor by rough handling during storage, assembly or operation, leading to an open failure. The failure can occur invisibly inside the packaging and is measurable.^[2]
• Increase of dissipation factor due to contamination of capacitor materials, particularly from flux and solvent residues.^[2]

Electrolytic capacitors

In addition to the problems listed above, electrolytic capacitors suffer from these failures:

• Aluminium versions having their electrolyte dry out for a gradual leakage, equivalent series resistance and loss of capacitance. Power dissipation by high ripple currents and internal resistances cause an increase of the capacitor's internal temperature beyond specifications, accelerating the deterioration rate; such capacitors usually fail short.^[2]
• Electrolyte contamination (like from moisture) corroding the electrodes, leading to capacitance loss and shorts.^[2]
• Electrolytes evolving a gas, increasing pressure inside the capacitor housing and sometimes causing an explosion; an example is the capacitor plague.^{[citation needed]}
• Tantalum versions being electrically overstressed, permanently degrading the dielectric and sometimes causing open or short failure.^[2] Sites that have failed this way are usually visible as a discolored dielectric or as a locally melted anode.^[6]

Metal oxide varistors

Metal oxide varistors typically have lower resistance as they heat up; if connected directly across a power bus, for protection against voltage spikes, a varistor with a lowered trigger voltage can slide into catastrophic thermal runaway and sometimes a small explosion or fire.^[23] To prevent this, the fault current is typically limited by a thermal fuse, circuit breaker, or other current limiting device.

MEMS failures

suffer from various types of failures:

• Stiction causing moving parts to stick; an external impulse sometimes restores functionality. Non-stick coatings, reduction of contact area, and increased awareness mitigate the problem in contemporary systems.^[9]
• Particles migrating in the system and blocking their movements. Conductive particles may short out circuits like electrostatic actuators. Wear damages the surfaces and releases debris that can be a source of particle contamination.
• Fractures causing loss of mechanical parts.
• Material fatigue
  inducing cracks in moving structures.
• Dielectric charging leading to change of functionality and at some point parameter failures.^[24]

Recreating failure modes

In order to reduce failures, a precise knowledge of bond strength quality measurement during product design and subsequent manufacture is of vital importance. The best place to start is with the failure mode. This is based on the assumption that there is a particular failure mode, or range of modes, that may occur within a product. It is therefore reasonable to assume that the bond test should replicate the mode, or modes of interest. However, exact replication is not always possible. The test load must be applied to some part of the sample and transferred through the sample to the bond. If this part of the sample is the only option and is weaker than the bond itself, the sample will fail before the bond.^[25]

See also

• Reliability (semiconductor)

References

Further reading

• Herfst, R.W., Steeneken, P.G., Schmitz, J., Time and voltage dependence of dielectric charging in RF MEMS capacitive switches, (2007) Annual Proceedings – Reliability Physics (Symposium), art. no. 4227667, pp. 417–421.

External links

• http://www.esda.org - ESD Association