Engineering:Capacitor plague

Short description: Period of high failure rate of capacitors

Failed aluminium electrolytic capacitors with open vents in the top of the can, and visible dried electrolyte residue (reddish-brown color)

The capacitor plague was a problem related to a higher-than-expected failure rate of non-solid aluminium electrolytic capacitors between 1999 and 2007, especially those from some Taiwanese manufacturers, due to faulty electrolyte composition that caused corrosion accompanied by gas generation; this often resulted in rupturing of the case of the capacitor from the build-up of pressure.

High failure rates occurred in many well-known brands of electronics, and were particularly evident in motherboards, video cards, and power supplies of personal computers.

A 2003 article in The Independent claimed that the cause of the faulty capacitors was due to a mis-copied formula. In 2001, a scientist working in the Rubycon Corporation in Japan stole a mis-copied formula for capacitors' electrolytes. He then took the faulty formula to the Luminous Town Electric company in China, where he had previously been employed. In the same year, the scientist's staff left China, stealing again the mis-copied formula and moving to Taiwan, where they created their own company, producing capacitors and propagating even more of this faulty formula of capacitor electrolytes.

History

First announcements

The first flawed capacitors linked to Taiwanese raw material problems were reported by the specialist magazine Passive Component Industry in September 2002. Shortly thereafter, two mainstream electronics journals reported the discovery of widespread prematurely failing capacitors, from Taiwanese manufacturers, in motherboards.

These publications informed engineers and other technically interested specialists, but the issue did not receive widespread public exposure until Carey Holzman published his experiences about "leaking capacitors" in the overclocking performance community.

Public attention

Results of fire on a printed circuit board, caused by leaked electrolyte which short-circuited conductors carrying power

The news from the Holzman publication spread quickly on the Internet and in newspapers, partly due to the spectacular images of the failures – bulging or burst capacitors, expelled sealing rubber and leaking electrolyte on countless circuit boards. Many PC users were affected, and caused an avalanche of reports and comments on thousands of blogs and other web communities.

The quick spread of the news also resulted in many misinformed users and blogs posting pictures of capacitors that had failed due to reasons other than faulty electrolyte.

Prevalence

Most of the affected capacitors were produced from 1999 to 2003 and failed between 2002 and 2005. Problems with capacitors produced with an incorrectly formulated electrolyte have affected equipment manufactured up to at least 2007.

Major vendors of motherboards such as Abit, IBM, Dell, Apple, HP, and Intel were affected by capacitors with faulty electrolytes.

In 2005, Dell spent some US$420 million replacing motherboards outright and on the logistics of determining whether a system was in need of replacement.

Many other equipment manufacturers unknowingly assembled and sold boards with faulty capacitors, and as a result the effect of the capacitor plague could be seen in all kinds of devices worldwide.

Because not all manufacturers had offered recalls or repairs, do it yourself repair instructions were written and published on the Internet.

Responsibility

In the November/December 2002 issue of Passive Component Industry, following its initial story about defective electrolyte, reported that some large Taiwanese manufacturers of electrolytic capacitors were denying responsibility for defective products.

While industrial customers confirmed the failures, they were not able to trace the source of the faulty components. The defective capacitors were marked with previously unknown brands such as "Tayeh", "Choyo", or "Chhsi". The marks were not easily linked to familiar companies or product brands.

The motherboard manufacturer ABIT Computer Corp. was the only affected manufacturer that publicly admitted to defective capacitors obtained from Taiwan capacitor makers being used in its products. However, the company would not reveal the name of the capacitor maker that supplied the faulty products.

Symptoms

Common characteristics

The non-solid aluminium electrolytic capacitors with improperly formulated electrolyte mostly belonged to the so-called "low equivalent series resistance (ESR)", "low impedance", or "high ripple current" e-cap series. The advantage of e-caps using an electrolyte composed of 70% water or more is, in particular, a low ESR, which allows a higher ripple current, and decreased production costs, water being the least costly material in a capacitor.

Comparison of aluminium e-caps with different non-solid electrolytes

Electrolyte	Manufacturer series, type	Dimensions D × L (mm)	Max. ESR at 100 kHz, 20 °C (mΩ)	Max. ripple current at 85/105 °C (mA)
Non-solid organic electrolyte	Vishay 036 RSP, 100 µF, 10 V	5 × 11	1000	160
Non-solid, ethylene-glycol, boric-acid (borax) electrolyte	NCC SMQ, 100 µF, 10 V	5 × 11	900	180
Non-solid water-based electrolyte	Rubycon ZL, 100 µF, 10 V	5 × 11	300	250

Premature failure

All electrolytic capacitors with non-solid electrolyte age over time, due to evaporation of the electrolyte. The capacitance usually decreases and the ESR usually increases. The normal lifespan of a non-solid electrolytic capacitor of consumer quality, typically rated at 2000 h/85 °C and operating at 40 °C, is roughly 6 years. It can be more than 10 years for a 1000 h/105 °C capacitor operating at 40 °C. Electrolytic capacitors that operate at a lower temperature can have a considerably longer lifespan.

The capacitance should normally degrade to as low as 70% of the rated value, and the ESR increase to twice the rated value, over the normal life span of the component, before it should be considered as a "degradation failure". The life of an electrolytic capacitor with defective electrolyte can be as little as two years. The capacitor may fail prematurely after reaching approximately 30% to 50% of its expected lifetime.

Electrical symptoms

The electrical characteristics of a failed electrolytic capacitor with an open vent are the following:

• capacitance value decreases to below the rated value
• ESR increases to very high values.

Electrolytic capacitors with an open vent are in the process of drying out, regardless of whether they have good or bad electrolyte. They always show low capacitance values and very high ohmic ESR values. Dry e-caps are therefore electrically useless.

E-caps can fail without any visible symptoms. Since the electrical characteristics of electrolytic capacitors are the reason for their use, these parameters must be tested with instruments to definitively decide if the devices have failed. But even if the electrical parameters are out of their specifications, the assignment of failure to the electrolyte problem is not a certainty.

Non-solid aluminium electrolytic capacitors without visible symptoms, which have improperly formulated electrolyte, typically show two electrical symptoms:

• relatively high and fluctuating leakage current
• increased capacitance value, up to twice the rated value, which fluctuates after heating and cooling of the capacitor body

Visible symptoms

Closeup of a broken electrolytic capacitor vent and dried electrolyte residue

When examining a failed electronic device, the failed capacitors can easily be recognized by clearly visible symptoms that include the following:

• Bulging of the vent on top of the capacitor. (The "vent" is stamped into the top of the casing of a can-shaped capacitor, forming a seam that is meant to split to relieve pressure build-up inside, preventing an explosion.)
• Ruptured or cracked vent, often accompanied by visible crusty rust-like brown or red dried electrolyte deposits.
• Capacitor casing sitting crooked on the circuit board, caused by the bottom rubber plug being pushed out, sometimes with electrolyte having leaked onto the motherboard from the base of the capacitor, visible as dark-brown or black surface deposits on the PCB. The leaked electrolyte can be confused with thick elastic glue sometimes used to secure the capacitors against shock. A dark brown or black crust up the side of a capacitor is invariably glue, not electrolyte. The glue itself is harmless.

Visible symptoms of failed electrolytic capacitors

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  Failed Chhsi capacitor with crusty electrolyte buildup on the top

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  Failed capacitors next to CPU motherboard socket

• 

  Failed Tayeh capacitors which have vented subtly through their aluminium tops

• 

  Failed electrolytic capacitors with swollen can tops and expelled rubber seals, dates of manufacture "0106" and "0206" (January and February 2006)

• 

  Failed capacitor has exploded and exposed internal elements, and another has partially blown off its casing

• 

  Failed Choyo capacitors (black color) which have leaked brownish electrolyte onto the motherboard

Investigation

Implications of industrial espionage

Industrial espionage was implicated in the capacitor plague, in connection with the theft of an electrolyte formula. A materials scientist working for Rubycon in Japan left the company, taking the secret water-based electrolyte formula for Rubycon's ZA and ZL series capacitors, and began working for a Chinese company. The scientist then developed a copy of this electrolyte. Then, some staff members who defected from the Chinese company copied an incomplete version of the formula and began to market it to many of the aluminium electrolytic manufacturers in Taiwan, undercutting the prices of the Japanese manufacturers. This incomplete electrolyte lacked important proprietary ingredients which were essential to the long-term stability of the capacitors and was unstable when packaged in a finished aluminium capacitor. This faulty electrolyte allowed the unimpeded formation of hydroxide and produced hydrogen gas.

There are no public court proceedings related to the alleged theft, as Rubycon's complete electrolyte formula remained secure. However, independent laboratory analysis of defective capacitors has shown that many of the premature failures appear to be associated with high water content and missing inhibitors in the electrolyte, as described below.

Incomplete electrolyte formula

Unimpeded formation of hydroxide (hydration) and associated hydrogen gas production, occurring during "capacitor plague" or "bad capacitors" incidents involving the failure of large numbers of aluminium electrolytic capacitors, has been demonstrated by two researchers at the Center for Advanced Life Cycle Engineering of the University of Maryland who analyzed the failed capacitors.

The two scientists initially determined, by ion chromatography and mass spectrometry, that there was hydrogen gas present in failed capacitors, leading to bulging of the capacitor's case or bursting of the vent. Thus it was proved that the oxidation takes place in accordance with the first step of aluminium oxide formation.

Because it has been customary in electrolytic capacitors to bind the excess hydrogen by using reducing or depolarizing compounds, such as aromatic nitrogen compounds or amines, to relieve the resulting pressure, the researchers then searched for compounds of this type. Although the analysis methods were very sensitive in detecting such pressure-relieving compounds, no traces of such agents were found within the failed capacitors.

In capacitors in which the internal pressure build-up was so great that the capacitor case was already bulging but the vent had not opened yet, the pH value of the electrolyte could be measured. The electrolyte of the faulty Taiwanese capacitors was alkaline, with a pH of between 7 and 8. Good comparable Japanese capacitors had an electrolyte that was acidic, with a pH of around 4. As it is known that aluminium can be dissolved by alkaline liquids, but not that which is mildly acidic, an energy dispersive X-ray spectroscopy (EDX or EDS) fingerprint analysis of the electrolyte of the faulty capacitors was made, which detected dissolved aluminium in the electrolyte.

To protect the metallic aluminium against the aggressiveness of the water, some phosphate compounds, known as inhibitors or passivators, can be used to produce long-term stable capacitors with high-aqueous electrolytes. Phosphate compounds are mentioned in patents regarding electrolytic capacitors with aqueous electrolytic systems. Since phosphate ions were missing and the electrolyte was also alkaline in the investigated Taiwanese electrolytes, the capacitor evidently lacked any protection against water damage, and the formation of more-stable alumina oxides was inhibited. Therefore, only aluminium hydroxide was generated.

The results of chemical analysis were confirmed by measuring electrical capacitance and leakage current in a long-term test lasting 56 days. Due to the chemical corrosion, the oxide layer of these capacitors had been weakened, so after a short time the capacitance and the leakage current increased briefly, before dropping abruptly when gas pressure opened the vent. The report of Hillman and Helmold proved that the cause of the failed capacitors was a faulty electrolyte mixture used by the Taiwanese manufacturers, which lacked the necessary chemical ingredients to ensure the correct pH of the electrolyte over time, for long-term stability of the electrolytic capacitors. Their further conclusion, that the electrolyte with its alkaline pH value had the fatal flaw of a continual buildup of hydroxide without its being converted into the stable oxide, was verified on the surface of the anode foil both photographically and with an EDX-fingerprint analysis of the chemical components.

See also

• RKM code

Further reading

• H. Kaesche, Die Korrosion der Metalle - Physikalisch-chemische Prinzipien und aktuelle Probleme, Springer-Verlag, Berlin, 2011, ISBN:978-3-642-18427-7
• C. Vargel, Corrosion of Aluminium, 1st Edition, 2 October 2004, Elsevier Science, Print Book ISBN:978-0-08-044495-6, eBook ISBN:978-0-08-047236-2
• W. J. Bernard, J. J. Randall Jr., The Reaction between Anodic Aluminium Oxide and Water, 1961 ECS - The Electrochemical Society [8]
• Ch. Vargel, M. Jacques, M. P. Schmidt, Corrosion of Aluminium, 2004 Elsevier B.V., ISBN:978-0-08-044495-6
• Patnaik, P. (2002). Handbook of Inorganic Chemicals. McGraw-Hill. ISBN:0-07-049439-8.
• Wiberg, E. and Holleman, A. F. (2001). Inorganic Chemistry. Elsevier. ISBN:0-12-352651-5