The capacitor plague was a problem with a large number of premature failures of aluminum electrolytic capacitors with non-solid or liquid electrolyte of certain brands, especially from some Taiwanese manufacturers. The capacitors failed because of a special water based corrosion effect, due to a poorly formulated electrolyte.
The first flawed capacitors were reported in September 2002. Many publicized press releases about the widespread problem with premature failures of Taiwanese electrolytic capacitors appeared. Most of the affected capacitors failed in the early to middle years of the first decade of the 2000s. High failure rates occurred in various electronic equipment, particularly motherboards, video cards, compact fluorescent lamp ballasts, LCD monitors, and power supplies of personal computers. News of the failures (usually after a few years of use) forced many equipment manufacturers to repair the defects. As of 2013[update] the problem seems to have receded, with the last major surge of complaints being reported in 2010.
Faulty capacitors have been discovered in electronic equipment at various times, but mainstream electronics journals began to report widespread defective capacitors from Taiwanese manufacturers in motherboards around 2002/2003. Problems with "bad caps" have affected equipment manufactured up to at least 2007 and beyond. Many well-known motherboard companies have unknowingly assembled and sold boards with faulty capacitors sourced from other manufacturers. Major vendors such as IBM, Intel, Dell, HP, Samsung, and Apple Inc. were affected. Circa 2005, Dell spent some US$420 million replacing motherboards outright and on the logistics of determining whether a system was in need of replacement. HP reportedly purged its product line in 2004. The motherboards and power supplies in the Apple iMac G5 and some eMacs were also affected.
While the capacitor plague has affected large numbers of desktop computers, the problem is by no means limited to that category. Bad capacitors can also be found in external power supply adaptors, network switches, audio equipment, flat panel displays, and a wide range of other devices. "Bad caps" can cause a simple failure to turn on, or a wide range of bizarre (often intermittent) behavior of afflicted electronic equipment.
In failures of general electronics devices, "bad caps" are often found in the power supply circuitry. In failed computer systems, "bad caps" are often found in power supply units, but also on motherboards next to CPUs, and soldered near GPUs.
Visual symptoms 
Direct visual inspection is a common method of identifying capacitors which have failed because of bad electrolyte. Failed capacitors may show one or more of these visible symptoms:
- Bulging or cracking of the vent on top of the capacitor (the "vent" is shaped by an impression stamped into the top of the can, forming the seams of the vent. It is designed so that if the capacitor becomes pressurized it will split at the vent's seams, relieving the pressure rather than exploding.)
- Capacitor casing sitting crooked on the circuit board, as the bottom rubber plug is pushed out
- Electrolyte leaked onto the motherboard from the base of the capacitor or vented from the top, visible as crusty rust-like brown deposits. The petroleum-based adhesive that is sometimes used to secure the capacitors to the board if vibration or shock occurs during transportation can be confused with leaked electrolyte; electrolyte is usually wet, adhesive is dry. The glue is a thick elastic covering usually of a sandy yellow color, which darkens (towards black) with heat. A dark brown crust up the side of a capacitor is invariably glue, not electrolyte. The glue is itself sometimes harmful if it contains chlorine, and can corrode leads and tracks covered by it, causing leakage current or an open circuit; it is often not required for anything else than transport and can be removed if application is without vibration or shock. The presence of black-colored glue is a reliable sign that the capacitor has overheated, due either to internal failure or to inadequate ventilation.
- Detached or missing capacitor casing. Sometimes a failed capacitor will literally explode, ejecting its contents violently and shooting the casing off the circuit board. Grayish aluminum foil and shredded paper (the remnants of the capacitor internals) may still be attached to the circuit board, or scattered in the vicinity.
Sometimes, electrolytic capacitors fail without any visible changes in appearance of the external SMD or metal can package. Since the electrical characteristics of capacitors are the reason for their use, these parameters must be tested with instruments to definitively decide if the devices have failed.
Electrical symptoms 
As an electrolytic capacitor ages, its capacitance usually decreases and its equivalent series resistance (ESR) usually increases. The capacitance may abnormally degrade to as low as 4% of the original value, as opposed to an expected 50% capacity degradation over the normal life span of the component. When this happens, the capacitors no longer adequately serve their purpose of filtering the direct current voltages on the motherboard, and a result of this failure is an increase in the ripple voltage that the capacitor is supposed to filter out. This results in a system instability. Capacitors with high ESR and low capacitance can make power supplies malfunction, sometimes causing further circuit damage. In computers, CPU core voltage or other system voltages may fluctuate or go out of range, possibly with an increase in CPU temperature as the core voltage rises.
Computer symptoms 
Some common behavioral symptoms of "bad caps" seen in computer systems are:
- Intermittent failure to turn on, requiring user to press reset or try turning the computer on repeatedly
- Instabilities (hangs, occurrences of the "Blue Screen of Death", kernel panics, etc.), especially when symptoms get progressively more frequent over time
- Memory errors, especially ones that get more frequent with time
- Spontaneous restarts or resets
- In on-board or add-on video cards, unstable image in some video modes
- Failure to complete the Power-On Self Test ("POST"), or spontaneous rebooting before it is completed
- Failure to even start the POST; fans spin but the system appears dead
Unlike physical signs which are conclusive evidence that the capacitors are failing, many of the operational signs may be caused by other factors, such as a failing power supply (often due to failing capacitors within this sub-unit), dust clogging a fan, bad RAM, or other hardware problems. Once the operating system has loaded, instability might also indicate a software problem (such as some types of malware, poorly-written device drivers or software), and not a hardware problem at all. Computer crashes or hangs may occur only when the system is heavily loaded, which can cause marginal hardware to fail, but which also can activate obscure software bugs. The wide variety of possible symptoms makes it difficult to quickly and definitively diagnose a capacitor plague problem, in the absence of a well-recognized pattern of characteristic failures. Some particularly exasperating intermittent problems may be repeatedly misdiagnosed, and only resolved by wholesale replacement of an entire system.
If any of the listed symptoms are experienced, removing the system unit's case and inspecting the capacitors, especially those around the CPU, may immediately identify bad capacitors as the cause. However, if there are no physical signs, an oscilloscope may be used to examine the AC ripple voltage across capacitors during operation, or an ESR meter may be used to measure ESR on a powered-down system. Excessive ripple voltage or ESR is a definitive sign that the capacitors are faulty.
|Visible symptoms of failed electrolytic capacitors (click each image for enlarged view)|
Industrial espionage implicated 
The large number of failures of aluminum electrolytic capacitors with liquid electrolytes are based on millions of faulty capacitors produced in the years 1999 to 2007 by some (not all) Taiwanese manufacturers whose products started failing prematurely after only a few months of operation. Many of the capacitors had a life span specification (load life) of 2000 hours at 105°C. With a lower average internal temperature of 45°C on a printed circuit board and a ripple current within the data sheet specifications, these capacitors should have a life expectancy of about 18 years of continuous operation; a failure after 1.5 to 2 years is very premature.
The images of the failures were quite spectacular — bulged or burst cans, expelled sealing rubber and leaking electrolyte were found on countless circuit boards. Many well-known equipment manufacturers such as Apple, Dell, Cisco, Intel, Asus and Abit had to carry out recalls and reimburse repair costs because of these capacitors. In addition to manufacturer recall programs, detailed repair instructions for self-help can be found on the Internet.
A major cause of the plague of faulty capacitors was industrial espionage in connection with the theft of an electrolyte formula. A researcher is suspected of having taken, when moving from Japan to Taiwan, the secret chemical composition of a new low-resistance, inexpensive, water-containing electrolyte. The researcher subsequently tried to imitate this electrolyte formula in Taiwan, to undersell the pricing of the Japanese manufacturers. However, the secret formula had apparently been copied incompletely, and it lacked important proprietary ingredients which were essential to the long-term stability of the capacitors.
There are no known public court proceedings related to alleged theft of electrolyte formulas. However, independent laboratory analysis of defective capacitors has shown that many of the premature failures do appear to be associated with high water content and missing inhibitors in the electrolyte, as described below.
Development of electrolytic capacitors with water-based electrolytes 
|Internal structure of an electrolytic capacitor with non-solid electrolyte|
The first electrolytic capacitor produced was an aluminum electrolytic capacitor with a liquid electrolyte, invented by Charles Pollak in January 1896. Modern electrolytic capacitors are based on the same fundamental design. On an aluminum anode, a dielectric of a very thin aluminum oxide layer is deposited chemically. A liquid electrolyte in intimate contact with the dielectric layer forms the liquid cathode of the capacitor. A spacer made of paper prevents direct contact of the oxide layer with a second aluminum foil (cathode foil), which provides the electrical connection to the liquid cathode. Hermetically sealed and provided with terminal connections, this design is used in billions of inexpensive and reliable (within their specified life span) capacitors used for electronic devices.
The electrolyte as an ionic conductor causes most of the ohmic (resistive) losses in the capacitor. Great efforts have been made over the years to reduce these losses thus increasing the ripple current handling capability, because without such improvements the most important target of development — size reductions (volumetric efficiency) — cannot be realized.
With this goal in mind, some Japanese manufacturers have developed a new, low-ohmic water-based class of electrolytes. The conductivity of water-based electrolytes compared to electrolytes with organic solvents like GBL was significantly improved. Water, with its relatively high permittivity of ε = 81, is a powerful solvent for electrolytes. As such, it dissolves salts in high concentration. The high concentration of dissolved salt ions in the electrolyte increases the conductivity. But water will react quite aggressively and even violently with unprotected aluminum. It converts metallic aluminum (Al) via a highly exothermic reaction into aluminum hydroxide (Al(OH)3). This is accompanied by strong heat and gas development in the capacitor, and may even lead to the explosion of the capacitor. Therefore, the main problem in the development of new water-containing electrolytes is to hinder the aggressiveness of the water against aluminum, to get capacitors having a sufficiently good long-term stability.
The Japanese manufacturer Rubycon was a leader in the development of new water-based electrolyte systems with enhanced conductivity in the late 1990s. In 1998, Rubycon announced two series, ZL and ZA, of the first capacitors on the market using an electrolyte with a water content of about 40%, which were suitable for a wide temperature range from −40 to +105°C.
The improvement achieved in the conductivity of the new electrolyte can be seen by a comparison of two capacitors, both of which have a nominal capacitance of 1000 µF at 16 V nominal voltage in a package with a diameter of 10 mm and a height of 20 mm. The capacitors of the Rubycon YXG series are provided with an electrolyte based on an organic solvent, and can attain an impedance of 46 milliohms when loaded with a ripple current of 1400 mA. ZL series capacitors with the new water-based electrolyte can attain an impedance of 23 milliohms with a ripple current of 1820 mA, an overall improvement of 30%.
Other manufacturers, such as NCC, Nichicon, and Elna followed with their own new products a short time later. The new type of capacitor was called "Low-ESR" or "Low-Impedance", "Ultra-Low-Impedance" or "High-Ripple Current" series in the data sheets. The highly competitive market in digital data technology and high-efficiency power supplies adopted these new components rapidly, because of their improved performance. Even better, by improving the conductivity of the electrolyte, capacitors not only can withstand a higher ripple current rating, they are even cheaper to produce, since water is very low cost compared to other solvents. Better performance and low cost drove widespread adoption of the new capacitors for high volume products like PCs, LCD screens and power supplies.
Aluminum oxide — solid dielectric and corrosion protection 
The electrolyte in an electrolytic capacitor is from an electrical point of view, the actual cathode of the capacitor. But it is also a chemical mixture, an acid or alkali, which must be non-corrosive (chemically inert) so that the capacitor, whose inner components are made of aluminum, remains stable over its expected lifetime. But aluminum is a very reactive, easily oxidized metal, and aqueous alkali solutions behave quite aggressively against aluminum. Only a stable aluminum oxide (Al2O3) layer on the surface of the aluminum anode, aided by protective substances known as inhibitors or passivators in the electrolyte, is able to protect metallic aluminum from water-driven corrosive reactions.
The fundamental issue of water-containing electrolyte systems lies in the control of aggressiveness of the water towards metallic aluminum. This issue has dominated the development of electrolytic capacitors over many decades. The first commercially-used electrolytes in the mid-20th century were mixtures of ethylene glycol and boric acid. But even these so-called glycol electrolytes had an unwanted chemical water-crystal reaction, according to the scheme: "acid + alcohol" → "ester + water". Thus, even in the first apparently water-free electrolytes, esterification reactions could generate a water content of up to 20%. These early electrolytes were originally suitable only for a limited temperature range of -25 to +85°C. They had a voltage-dependent life span, because at higher voltages the leakage current based on the aggressiveness of the water would increase exponentially, and the associated increased consumption of electrolyte would lead to a faster drying out and eventual failure.
On the other hand, water contains the oxygen needed for "self-healing" of electrolytic capacitors, via the so-called "formation" of anodic aluminum oxide, the dielectric layer of the capacitor. This normal process of oxide formation or self-healing is carried out in two reaction steps. First, a strongly-exothermic reaction transforms metallic aluminum (Al) into aluminum hydroxide, Al(OH)3:
- 2 Al + 6 H2O → 2 Al(OH)3 + 3 H2 ↑
This reaction is accelerated by a high electric field and by high temperatures, and is accompanied by a pressure buildup in the capacitor housing, caused by the released hydrogen gas. The gel-like aluminum hydroxide Al(OH)3 (also called alumina trihydrate (ATH), aluminic hydroxide, aluminum(III) hydroxide, or hydrated alumina) is converted, via a second reaction step (usually slowly over a few hours at room temperature, more rapidly in a few minutes at higher temperatures), into the crystalline form of aluminum oxide, Al2O3:
- 2 Al(OH)3 → 2 AlO(OH) + 2 H2O → Al2O3 + 3 H2O
Only newly-formed stable aluminum oxide can heal naturally-occurring microscopic "pinhole" defects that are present in a leaky dielectric layer on the anode of the electrolytic capacitor, forming a stable dielectric for the capacitor. The oxide also protects the capacitor from the aggressive reactions of metallic aluminum in the presence of water. However, with the conversion process of dielectric forming or self healing, a small amount of water from the electrolyte will be consumed by these chemical reactions. The net reaction is that oxygen from the water is used to form aluminum oxide dielectric, while the gaseous hydrogen diffuses out of the capacitor (provided that it is not generated too rapidly) or is scavenged by special chemicals added to the electrolyte for that purpose..
Aluminum hydroxide — loss of self-healing 
|Scanning electron microscope (SEM) images of failed electrolytic capacitors|
The aluminum oxide layer in the electrolytic capacitor is resistant to chemical attacks, as long as the pH value of the electrolyte is in the range of pH 4.5 to 8.5. However, the pH value of the electrolyte is ideally about 7 (neutral). Measurements of leakage current, which were carried out as early as the 1970s have shown that the leakage current is increased due to chemically induced defects when the pH value deviates from this ideal value. It is also known that the "normal" course of building a stable aluminum oxide layer by the transformation of aluminum through the intermediate step of aluminum hydroxide can be interrupted by an excessively alkaline or basic electrolyte. For example, alkaline disruption to the chemistry of this reaction results instead in the following reaction:
- 2 Al (s) + 2 NaOH (aq) + 6 H2O → 2 Na+ (aq) + 2[Al(OH)4]− (s) + 3 H2 (g)
In this case, it may happen that the hydroxide formed in the first step becomes mechanically detached from the metallic aluminum surface and will be not be transformed into the desired stable form of aluminum oxide. The initiating cause of the healing process for building a new oxide layer, a defect or a weak dielectric point, remains unremediated. Then there is further additional formation of aluminum hydroxide at this point, which occurs without converting into the stable aluminum oxide. The self-healing of the oxide layer inside the electrolytic capacitor no longer takes place. The reactions do not come to a standstill, since the hydroxide in the pores of the anode foil grows and the first reaction step produces more and more hydrogen gas in the can, increasing the pressure.
Evidence of defective electrolyte 
|Autopsy of a failed electrolytic capacitor|
The situation of unimpeded formation of hydroxide (hydration) and associated hydrogen gas production occurred during "capacitor plague" or "bad capacitors" incidents involving the failure of large numbers of aluminum electrolytic capacitors. This has been demonstrated by two researchers at the University of Maryland who analyzed the failed capacitors. They initially determined, by ion chromatography and mass spectrometry, that there really is hydrogen gas present in failing capacitors, which is what leads to bulging of the capacitor’s case or bursting the vent. Thus it was proved that the oxidation takes place according to the first step of the formation of aluminum oxide.
Because it has been customary in electrolytic capacitors to bind the excess hydrogen with the help of reducing or depolarizing compounds to reduce the resulting pressure, the researchers then searched for compounds of this type. Usually aromatic nitrogen compounds or amines are used for this purpose. Although the above-mentioned analysis methods are very sensitive to detecting such pressure-relieving compounds, no traces of such agents were found within the failed capacitors.
With 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, then the pH value of the electrolyte could be measured. The electrolyte of the faulty Taiwanese capacitors was alkaline with pH (7 < pH < 8). Comparable Japanese capacitors on the other hand had an electrolyte with a pH in the acidic range (pH ≈ 4). As it is known that aluminum can dissolve in alkaline liquids, but not in mildly acidic media, then with the electrolyte of the faulty capacitors an energy dispersive X-ray spectroscopy (EDX or EDS) fingerprint analysis was made, which actually detected dissolved aluminum.
To protect the metallic aluminum 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 to electrolytic capacitors with aqueous electrolytic systems. Since in the investigated Taiwanese electrolytes, phosphate ions were missing and the electrolyte was also alkaline, they evidently lacked any protection against water, and the formation of more-stable alumina oxides was inhibited. Therefore, only aluminum hydroxide was generated.
The results of chemical analysis were reinforced by the measurement of electrical capacitance and leakage current in a long-term test lasting 56 days. Due to the chemical attack, the oxide layer of these capacitors had been weakened, so that after a short time the capacitance and the leakage current increased briefly, before both parameters dropped abruptly upon opening of 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. The further conclusion that the electrolyte with its alkaline pH value then had the fatal flaw of continual growth of hydroxide wíthout conversion 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.
|Micrograph and EDX analysis of the anode surface|
Even in a microscopic image with only 10-fold magnification, as shown in the pictures above, a significant change in the structure of the anode surface is visible. On the surface of the "fresh" anode from an unused electrolytic capacitor the parallel scratches from manufacturing processing of the anode are clearly visible. However, the enlargement is not sufficient to show the openings of the pores in the anode, which are visible using a scanning electron microscope (SEM). In the picture of the used anode, which comes from a failed capacitor out of Taiwanese production, the surface is overgrown with a plaque-like substance transverse to the running direction of the scratches. An EDX-fingerprint analysis showed the chemical difference in the surface oxide. The surface of the "fresh" electrolytic capacitor was covered with stable aluminum oxide. The surface of the failed capacitor was covered with unstable aluminum hydroxide; the EDX scan shows a significantly higher oxygen peak.
Electrical effects 
|Measured electrical characteristics|
A slightly different electrical behavior of almost all electrolytic capacitors with water-based electrolytes can be measured in comparison to electrolytic capacitors with electrolyte systems based on organic solvents. The turn-on current leakage after a period of disuse is at a higher level for water-based electrolytes. However, if a water-based electrolyte is still in stable condition, not yet fallen into the alkaline pH range, then the leakage current declines after a few minutes, to a low value. Any pinhole defects that had been formed by the aggressive behavior of water on aluminum are healed quickly. But if the electrolyte pH has drifted into the alkaline range, then the process of dielectric self-healing will end after the formation of aluminum hydroxide. The subsequent conversion into stable aluminum oxide is prevented by the alkaline environment. The pinhole defects that cause the leakage current remain, covered only by hydroxide, and can be further attacked by the water in the electrolyte.
The dielectric strength of the hydroxide only can reach the level of the operating voltage applied, which is usually lower than the rated voltage. The decreased dielectric breakdown voltage of the anode can be measured. Pictured above, a typical measurement result is shown. The reduced dielectric breakdown voltage compared to the original anode breakdown voltage shows that a chemical process has caused damage to the oxide layer of the anode. This damage decreases the thickness of the insulating dielectric layer, which means according to the formula of the plate capacitor,
with the permittivity "ε", the electrode surface "A" and the distance between the electrodes to each other "d", that with a thinner dielectric the capacitance value increases. And indeed, electrolytic capacitors at the beginning of the fatal continual growth of hydroxide, showing a little bulging of the can but with the vent not yet open, exhibit an increased capacitance value. This temporary increase can be measured, as shown in the red-colored capacitance curve in the life test in the picture above. The final stage of this process is reached when the hydrogen gas generated by the constant continual growth of aluminum hydroxide has increased to such a high pressure that the vent pops open or the sealing rubber is expelled. Simply said, the capacitor bursts, whether quietly or catastrophically. Once the capacitor has opened its vent, it dries out very quickly, and drops its capacitance down to a minimum value while the ESR increases significantly up to the kilohm range. Because the ripple current still flows through the capacitor's now-higher ESR, the heat losses grow, rapidly increasing the temperature of the electrodes up to an overheat situation, and discoloring the paper separator to brown.
Electrolytic capacitor failures after 2007 
|SEM image and EDX fingerprint analysis|
Continuing failures 
The first publicized press releases about the widespread problem with premature failures of Taiwanese electrolytic capacitors appeared in September 2002. It might be assumed that by mid-2003 the affected capacitor manufacturers would have changed their production process and used a "correct" electrolyte mixture. With a typical shortened life span of about 1.5 to 3 years for the failing capacitors from mid-2003 up to mid-2006, the last of the bad capacitors should have failed by 2007. Commentators on the Internet often predicted the year 2007 would be the end point for "bad capacitors".
In theory, the defective capacitors should have "failed out" of active use, and very few new incidents should occur. But even after the year 2007, the year in which the failure of Taiwan bad capacitors with the wrong electrolyte should really be over, new complaints about failed capacitors are reported on the Internet.
The problem of bursting electrolytic capacitors still exists even with non-faulty wet e-caps, and recent images of failed capacitors show identical effects with open vents and expelled rubber plugs. Affected by these symptoms are capacitor series for rated voltages from 6.3 V to 100 V, which have one thing in common, they have a water-based electrolyte with a high water content of up to 75 %. In the catalogs of the manufacturers, they are characterized by the catchword "Low-ESR" capacitors or "Low-Impedance", "Ultra-Low-Impedance" or "High-Ripple-Current" capacitors. Electrolytic capacitors with these water-based electrolytes often show the same symptoms of corrosion caused by high electrical ripple current load or high thermal load or both together reaching the point of life end in a very short time. This behavior is quite different from wet electrolytic capacitors with non-aqueous organic electrolytes. Reaching the end of life this e-caps simply dry out with corresponding worse electrical values but without any visual signs.
These electrolytic capacitors must not be confused with aluminum-polymer solid-electrolyte capacitors, which are also often called "Low-ESR" electrolytic capacitors.
High ripple current and temperature 
The commonly-used 10-degree rule (Arrhenius equation, RGT-rule) to estimate a capacitor's life span (10°C reduction in temperature doubles the life span) often is not valid for electrolytic capacitors with water-based electrolytes. The 10-degree rule applies only when it is confirmed by the respective capacitor manufacturer.
Some manufacturers specify different life calculation formulas, sometimes even different formulas for their various series. Even though a graphical method may be specified to estimate the life span of a capacitor by a manufacturer and it may seem that the curves follow the 10-degree-law, one should not be fooled. In the following example, the slope of the specified curve is different than under the 10-degree rule.
The following two examples of electrolytic capacitor life calculations show the difference in results between the 10-degree rule and the formula that the manufacturer Rubycon has specified for their water-based electrolyte Series ZL.
For a personal computer power supply, a capacitor with the life span specification of 1000 hours at 105°C is selected. The average operating temperature of the capacitor, measured in the metallic region near the vent is 45°C. The ripple current load in the first example corresponds to the specified data sheet value (100%). This gives a predicted life of:
- 10-degree rule: 64,000 h, 7.3 years
- Rubycon formula: 64,000 h, 7.3 years
For a second example, the data sheet value for double the ripple current is obtained. This gives a predicted life of:
- 10-degree rule: 22.600 h, 2.6 years
- Rubycon formula: 6000 h, 0.7 years
The calculated life span at twice the value of the ripple current following the formula from Rubycon is significantly smaller than is predicted by the 10-degree rule. This reflects the fact that the operation of capacitors with water-based electrolytes at ripple current overload can be problematic. This is also reflected in a disclaimer of many capacitor manufacturers, who warn against operation with a higher ripple current than the specified maximum:
The difference in shortening the life span of electrolytic capacitors at higher loads, when comparing electrolytic capacitors with water-based electrolytes with those with electrolytes based on organic solvents, is due to the aggressiveness of the water against metallic aluminum. Capacitors with solvent electrolytes such as GBL have a significantly better leakage current behavior than those with water-based electrolytes. Because of the higher leakage current of water-based capacitors, they consume more electrolyte, thereby reducing the life of the capacitors. Measuring the dielectric strength of a cathode from a failed 10 V electrolytic capacitor, the specification was >1.5 V, and the measured dielectric strength was 2.9 V.
In addition, a high ripple current load can also result in consumption of electrolyte, especially during discharging of the capacitor. This is based on a physical effect that can sometimes lead to an abnormal "forming" process on the cathode foil in the capacitor. Normally the cathode foil is only covered with a minimal oxide layer that is formed naturally by contact with air on the aluminum surface. This oxide layer has a dielectric strength at room temperature of about 1 up to 1.5 V. At 105°C, the dielectric breakdown voltage decreases to about 0.7 to 1.2 V.
Now, if a charged capacitor is overly discharged during the discharging parts of the ripple current, then the polarity of the capacitor reverses: The cathode becomes an anode, the current flows out of the capacitor. Then the voltage distribution over the internal resistances builds up a voltage of opposite polarity to the cathode foil. The natural dielectric strength of the cathode oxide now can withstand the discharging loads up to the specified value in the relevant data sheet if the electrolytic capacitor has a correct design. The capacitor has a correct construction when the cathode capacitance CK is very large compared to the anode capacitance CA. This is usually the case when the cathode capacitance is a factor of 10 larger than the anode capacitance. However, increasing the ripple current load over the specified value, especially when the temperature is high, may generate a reverse voltage to the cathode foil higher than the natural dielectric strength, and may form up the oxide on the cathode foil. Formation of a thicker oxide layer on the cathode foil consumes electrolyte, which reduces the life span of the capacitor.
End-of-life processes 
The life span of an electrolytic capacitor with high water content in the electrolyte is thus determined not only by the operating temperature and the corresponding gradual evaporation of the electrolyte, but also by the leakage current and a possible forming process of the cathode foil at high ripple current load. All these factors, namely, the evaporation of electrolytes, the higher leakage current for capacitors with water-based electrolytes and, if it is applied, a high ripple current, will use up fluid electrolytes. From a certain point at the saturation limit for dissolved salts in the electrolyte, the salts will crystallize. As the electrolyte changes, initially the conductivity of the electrolyte decreases, and the ESR increases. For some product designs, the change in the electrolyte also may have an influence on the pH, which may deteriorate more rapidly as the end of the service life of electrolytic capacitors approaches.
When the pH of the electrolyte at the end of life moves into the alkaline region, which occurs often in capacitors with water-based electrolytes, the regeneration of pinhole defects ceases, and the fatal, unrestrained growth of aluminum hydroxide begins. When this behavior coincides with the end of predicted life and the electrolytic capacitor bursts, it may still look as if a new case of the "capacitor plague" has occurred.
The failure scenarios, involving a burst electrolytic capacitor, expelled sealing rubber, and leaked electrolyte are identical to those of capacitor production with the "wrong" electrolyte. If now with capacitors built after the year 2007, failures of this kind occur, it only can be determined by a careful recalculation of the entire circuit with all load conditions for the capacitor, such as temperature and ripple current load, whether there was a defect in the capacitor or an error in the design of the circuit.
Only when the capacitor fails prematurely, before it reaches the end of its calculated design life, may it be concluded that there is a faulty electrolyte versus some other failure cause. The root cause for failures was important in a court case between a well-known manufacturer of computer hardware and a capacitor manufacturer which occurred well after 2007.
Either an incorrect calculation of the service life or a faulty electrolyte results in the same failure scenario. However, bursting of an electrolytic capacitor, even if it has reached its end of life, is an extraordinary process. Until the widespread appearance of the capacitor plague problem, it could be assumed that electrolytic capacitors would very gradually dry out over time, showing no visible abnormalities. Now, it seems that water-based electrolytes in electrolytic capacitors of some manufacturers can cause a catastrophically different behavior at the end of life — they burst! When analyzing a prematurely-burst capacitor, it cannot be immediately determined whether thermal or electrical overload has led to the opening of the vent, or if the failure is due to a faulty electrolyte. Therefore, for a correct assessment of recent failures involving electrolytic capacitors, it is necessary to determine the exact operating conditions and to calculate the expected service life according to the manufacturer's specifications.
Date of manufacture code 
Many manufacturers use a 2-character abbreviation according to the IEC 60062 standard, to code the date of production (date code) of electrolytic capacitors:
- First character: Year of production, S = 2004, T = 2005, U = 2006, V = 2007, W = 2008, X = 2009, A = 2010, B = 2011, C = 2012, D = 2013
- Second character: Month of production, 1 to 9 = Jan. to Sept., O = Oct., N = Nov., D = Dec.
Example: X8 = August 2009
See also 
- "Capacitor plague", Facebook.
- "Badcaps" (forum). 2012-02-28. Retrieved 2012-03-07.
- Sperling, E; Morrison first3 = B, G; Levine, Got juice? Leaky capacitors shorting circuits; problem spreads – Taiwan-made capacitors causing problems.
- "Capacitor plague, identifizierte Hersteller" [Capacitor plague, identified vendors]. Open circuits. 2012-01-10. Retrieved 2012-03-07.
- Carey Holzman, Overclockers, Capacitors: Not Just For Abit Owners, 10. Sept. 2002, 
- Houtman, Ron (2010-09-01). "R. Houtman, September 1, 2010, The capacitor plague strikes again!". Ronhoutman.com. Retrieved 2012-03-07.
- Chiu, Samuel K; Moore (February 2003). "Faults & Failures: Leaking capacitors muck up motherboards". IEEE Spectrum 40 (2): 16–17. doi:10.1109/MSPEC.2003.1176509. ISSN 0018-9235. Retrieved 2012-03-08.
- "Motherboard Capacitor Problem Blows Up". Silicon Chip. AU. 2003-05-11. Retrieved 2012-03-07.
- Vance, Ashlee (June 28, 2010). "Suit Over Faulty Computers Highlights Dell’s Decline". The New York Times. Retrieved 2012-03-08.
- Defekte PCs: Dells Gewinnmotor stottert (in German), Preß etext.
- "Apple iMac Repair Extension Program". Apple. 2008-12-15. Retrieved 2012-03-07.
- "Repair Extension Program". eMac. Apple. Retrieved 2012-03-07.
- "Bad Capacitors: Information and symptoms". Lowyat. 100211.
- Leeper, Low-ESR Aluminium Electrolytic Failures Linked to Taiwanese Raw Material Problems (PDF), Molalla.
- "Mainboardhersteller steht für Elko-Ausfall gerade", Heise (in German) (online ed.) (DE), 14.04.2005.
- Capacitor Replacement Video Tutorial (HD) (video), Afro tech mods.
- Repair and bad capacitor information, Capacitor Lab.
- "Products". JP: Rubycon. Retrieved 2012-03-07.
- Uzawa, Shigeru; Komatsu, Akihiko; Ogawara, Tetsushi, Ultra Low Impedance Aluminum Electrolytic Capacitor with Water based Electrolyte, Rubycon.
- "Catalog". NCC, ECC. JP: Chemi-con. Retrieved 2012-03-07.
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