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Aluminum electrolytic capacitor Effect of Halogens

Effect of Halogens.
 1  Effect of Flux
 2  Cleaning Agents
 3 Adhesive and Coating Materials
 4  Effect of Fumigation

Effect of Halogens.
Aluminum electrolytic capacitors are sensitive to contamination of halogen ions (especially to chlorine and bromine ions) though the degree of the effect depends on the properties of the electrolyte and/or sealing materials used in the capacitors. For using a halide-containing flux, solvent (cleaning agent, adhesive or coating materials) or fumigant, the halide may penetrate into the capacitor through the rubber seal materials and cause the following corrosion reactions to occur. These reactions can lead to an increase in leakage current, opening of the pressure relief vent, and/or open-circuit failure in the capacitor. The reactions are accelerated as the voltage and/or temperature rises.

[Corrosion reactions]
a)Decomposition of halides
b)Corrosion reactions RX:Halogenated compound
X-:Halogen ions(Cl-, F-, Br-)

Halides that penetrated the element inside a capacitor make contact with the electrolyte, by which the halides are hydrolyzed and release halogen ions as shown on Reaction (21). The halogen ions then attack aluminum by anodic half-cell reaction, producing AlX3 (Reaction 22 and 23).
AlX3 is then hydrolyzed, which is decomposed to aluminum hydroxide and the halogen ions (Reaction (24)). The halogen ions reproduced are repeatedly used and reproduced by the reactions of (22) ~ (24), and then the corrosion develops endlessly.
Shown below are precautions for use of flux, cleaning agents, adhesive, coating materials and fumigant.
1  Effect of Flux
Usually flux products contain an activator of ionic halide system, which has been associated with the corrosion issues of capacitors, and nowadays non-ionic halide system type flux products have been increasingly available on the market. Some of the latter flux type have been classified into the so called “non-halogen flux” or “halogen-free flux”, and parts of the “non-halogen” or “halogen-free” flux products may contain a large amount of non-ionic halides, which can also adversely affect the capacitors.
2  Cleaning Agents
Where cleaning the solvent resistance type of aluminum electrolytic capacitors, confirm the following conditions:
a. C ontrol the contamination (the conductivity, pH, specific gravity, water content, etc.) of the cleaning agents.
b. A fter the cleaning, do not leave the capacitors (assembly boards) in an environment of cleaning agent-rich or in a closed container. Sufficiently evaporate the residual cleaning agent from the assembly boards and the capacitors by forced hot air at temperatures less than the upper limit of category temperature range for more than 10 minutes. In general, aluminum electrolytic capacitors are sensitive to contamination of halogen ions (particularly to chlorine ions). Depending on the properties of the electrolyte and rubber seal materials used in a capacitor, the halogen ions lead up to catastrophic failures on the capacitor. Where the inside of a capacitor has been contaminated with more than a certain amount of halogen ions and the capacitor is in use, the corrosion reaction of aluminum occurs. The corrosion causes the capacitor to have a significant increase in leakage current with heat produced, open the pressure relief vent and become open circuit mode failure.
Due to global environmental issues (greenhouse effects and other environmental destruction by depletion of the ozone layer), the conventional cleaning solvents of CFC 113, Trichloroethylene and 1,1,1-trichloroethylene were replaced by substitutes.

2-1 Alcohol Cleaning Agents
Fatty-alcohol cleaning agents (New type of solvent)
Pine Alpha ST-100S (Arakawa Chemical)
Clean Through 750H, 750K, 750L, and 710M (Kao)
Technocare FRW-14 through 17 (GE Toshiba Silicones)
 IPA (Isopropyl alcohol)
[Compatible capacitor products]

[Cleaning conditions]
Either of Immersion or ultrasonic cleaning, for a maximum of 10 minutes at a maximum liquid temperature of 60°C.
a.  Make sure that the markings on a capacitor are not rubbed against any other component or the PC board during cleaning. Note that shower cleaning can cause the markings on the capacitor to be washed off.
b.Depending on the cleaning method, the markings may be erased or blur.
c.drying process following a water cleaning or rinsing process may cause the outer sleeve materials of a capacitor to swell or shrink.
d.After using a weak-alkaline cleaning agent (e.g. Clean Through 750H), rinse with water to make sure that no alkaline residue is left on the capacitor.
e.Control a flux concentration in a cleaning agent within 2 wt%.
f.IPS (Isopropyl Alcohol), if containing xylene or other solvent to improve its cleanability, may swell the rubber seal materials.
g.Depending on the type of cleaning agent or conditions, note that the outer sleeve of a capacitor may lose a gloss or whiten in appearance.

2-2  HCFC (Freon-225), as Alternative CFCs
AK225AES (Asahi Glass)
[Cleaning conditions]
Solvent resistant type capacitors, which were originally developed to intend to resist Freon TE or Freon TES, are also capable of withstanding either of immersion or ultrasonic cleaning, for a maximum of 5 minutes (or 2 minutes for KRE series or 3 minutes for SRM series). However, in view of global environmental issues, HCFCs has not been recommended.
[Compatible capacitor products]

When a capacitor is mounted closely flush on the PC board, a residual cleaning agent may be left in the gap between the body of the capacitor and PC board surface. Dry out the residue with a forced hot air of 50 to 85°C for 10 minutes or more.
6-2-3 Other Solvents
To avoid capacitor failures, do not use the following cleaning agents:
・Halogenated system: causes capacitor failures due to corrosion.
・Alkali system: corrodes (dissolves) the aluminum can case.
・Terpene and petroleum system: deteriorates the rubber seal materials.
・Xylene and toluene: deteriorates the rubber seal materials as well.
・ Acetone: erases the markings printed on a capacitor.
3 Adhesive and Coating Materials
To use adhesives and/or coating materials for aluminum electrolytic capacitors, make sure of the following conditions:
a.Do not use any of adhesive or coating materials containing halogenated solvents.
b.No flux residue nor stain is left between the rubber seal of a capacitor and PC board.
c.Dry the capacitor to remove residual cleaning agents before applying adhesive and coating materials. Do not cover up the entire surface of the rubber seal of the capacitor with adhesive and coating materials.
d.Improper heating and/or curing conditions for adhesives and coating materials may cause the sleeve to swell or shrink. Please consult us for proper conditions.
e. For a non-solid aluminum electrolytic capacitor, covering up the entire surface of the rubber seal with resin mold materials will obstruct the normal diffusion of internal hydrogen gas from the capacitor and result in serious failures. Also, where the adhesive and coating materials contain a large amount of halogen ions, the halogen ions will contaminate the inside of the capacitor through the rubber seal materials, which cause the capacitor to become a failure.
f.The outer sleeve of a capacitor may lose a gloss or whiten in appearance depending on solvent materials that the adhesive or coating materials contains.
g.Some adhesives or coating materials contain organic solvent such as Xylene. Xylene can deteriorate the rubber seal materials, which cause the flux ingredients to penetrate into the capacitor.
4  Effect of Fumigation
In exporting or importing electronic devices, they may be exposed to fumigation with halide such as methyl bromide. Where aluminum electrolytic capacitors exposed to halide such as methyl bromide, the capacitors will be damaged with the corrosion reaction with the halogen ions. For the export and import, Nippon Chemi-Con considers using some packaging method and so forth that the fumigation is not required to. For customers to export or import electronic devices, semi-assembly products or capacitor components, confirm if they will be exposed to fumigation and also consider final condition of packaging. (Note that either cardboard or vinyl package has a risk of fumigation gas penetration.)

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