1. General Description Of Aluminum Electrolytic Capacitors
General Descriptions of Aluminum Electrolytic Capacitors1. General Description of Aluminum Electrolytic Capacitors1-1 Principles of Aluminum ElectrolyticCapacitors1-2 Capacitance of Aluminum ElectrolyticCapacitorsAn aluminum electrolytic capacitor consists of cathodealuminum foil, capacitor paper (electrolytic paper),electrolyte, and an aluminum oxide film, which acts as thedielectric, formed on the anode foil surface.A very thin oxide film formed by electrolytic oxidation(formation) offers superior dielectric constant and hasrectifying properties. When in contact with an electrolyte,the oxide film possesses an excellent forward directioninsulation property. Together with magnified effectivesurface area attained by etching the foil, a highcapacitance yet small sized capacitor is available.As previously mentioned, an aluminum electrolyticcapacitor is constructed by using two strips of aluminumfoil (anode and cathode) with paper interleaved. This foiland paper are then wound into an element andimpregnated with electrolyte. The construction of analuminum electrolytic capacitor is illustrated in Fig. 1-1.The capacitance of an aluminum electrolytic capacitormay be calculated from the following formula same as fora parallel-plate capacitor.-- 8 εS(1 - 1)(µF)C 8.855 10d;;;;;;;;;;;;;;;;;;;;;;Electrolyte(Real Cathode)Anode aluminumelectrodeOxide filmCathode Aluminumelectrode(Apparent Cathode)Electrolytic papercontaining electrolyteFig. 1 - 1Since the oxide film has rectifying properties, acapacitor has polarity. If both the anode and cathode foilshave an oxide film, the capacitors would be bipolar (nonpola) type capacitor.These technical notes refer to "non-solid" aluminumelectrolytic construction in which the electrolytic paper isimpregnated with liquid electrolyte. There is another typeof aluminum electrolytic capacitor, which is the "solid" thatuses solid electrolyte.ε : Dielectric constant of dielectricS : Surface area (cm2) of dielectricd : Thickness (cm) of dielectricTo attain higher capacitance "C", the dielectric constant" ε " and the surface area "S" must increase while thethickness "d" must decrease. Table 1-1 shows thedielectric constants and minimum thickness of dielectricsused in various types of capacitors.With aluminum electrolytic capacitors, since aluminumoxide has excellent withstand voltage, per thickness. Andthe thickness of dielectric can be freely controlledaccording to the rated voltage of the aluminum electrolyticcapacitor.Therefore, in compare to other dielectric, similar voltageendurance is provided by dielectric even if thickness ("d"in the above formula) is thin.Furthermore, by etching the surface of aluminum foil,the effective area of the foil as compared to the apparentarea can be enlarged 80 100 times for low voltagecapacitors and 30 40 times for middle / high voltagecapacitors. Therefore, aluminum electrolytic capacitorshave a higher capacitance for a specified apparent areathan other types of capacitors.High purity aluminum foil for the anode is etched byelectrochemical process in a chloride solution with DC,AC, or an alteration of DC and AC, or a concurring AC andDC current.Fine surface etching (photo 1-1)accomplished mainly by AC electrolysis is generally usedfor foil with a low voltage rating. Tunnel etching (photo 12) accomplished mainly by DC electrolysis is used formiddle / high voltage foil. The etching of the cathode foilis mainly accomplished by AC electrolysis to increase thesurface area.Table 1-1 Dielectric constants and minimum thickness of dielectrics used in various types of capacitorsType of CapacitorDielectricAluminum Electrolytic CapacitorAluminum OxideTantalum Electrolytic CapacitorFilm Capacitor (Metallized)Dielectric ConstantεDielectric Thickness d (µm)7 10(0.0013 0.0015/ V)Tantalum Oxide24(0.001 0.0015/ V)Polyester Film3.20.5 2Ceramic Capacitor (High Dielectric Constant Type)Barium Titanate500 20,0002 3Ceramic Capacitor (Temp. Compensation Type)Titanium Oxide15 2502 3TECHNICAL NOTES CAT.8101E-1NICHICON CORPORATION
General Descriptions of Aluminum Electrolytic CapacitorsSectionSurfacePhoto 1-1 Surface and section photo of etched aluminum foil for low voltage capacitors.Section (Replica)SurfacePhoto 1-2 Surface and section photo of etched aluminum foil for middle / high voltage capacitors.TECHNICAL NOTES CAT.8101ENICHICON CORPORATION
General Descriptions of Aluminum Electrolytic Capacitors1-3 Dielectric (Aluminum Oxide Layer)a0.0013 0.0015 (µm)/ V.Expanded photography of a dielectric (aluminum oxidelayer) on the foil that has not been etched (plain foil) isshown in photo 1-3.The fabrication reaction of the dielectric can beexpressed as follows: 3e - (Electron)2Al 3H2O a Al2O3 3H2 (Gas)dielectricdielectricdielectricA high purity etched aluminum foil is anodized in aboric acid-ammonium water type solution, for exsample,to form an aluminum oxide film on its surface. Thisaluminum oxide film is what we call the dielectric of thealuminum electrolytic capacitor. The DC voltage that isapplied to the foil to oxidize the anode foil is called"Forming Voltage".The thickness of the dielectric is nearly proportional tothe forming voltage and measures approximately20V Formed100V Formed250V FormedPhoto 1-3 Enlarged photo of oxide layer formed on a non-etched plain aluminum foil.Photo 1-4 Enlarged photo of middle, high voltage formed foil.(Condition of oxide layer formation in a pit)1-4 ElectrolyteAnode foil and a cathode foil facing each other areinterleaved with electrolytic paper and wound into acylindrical shape. This is called a "capacitor element." Atthis stage, it has configuration of a capacitor whenconsiders electrolytic paper and the aluminum oxide layerto be dielectric, however, the unit has few capacitance.When this capacitor element is impregnated with liquidelectrolyte, the anode foil and cathode foil are electricallyconnected. With the aluminum oxide layer formed on theanode foil acting as the sole dielectric, a capacitor with ahigh value of capacitance is now attainable. That is to saythat the electrolyte is now functioning as a cathode. Thebasic characteristics required of an electrolyte are listedbelow:(1) It must be electrically conductive.(2) It must have a forming property to heal any flaws onthe dielectric oxide of the anode foil.(3) It must be chemically stable with the anode andcathode foils, sealing materials, etc.(4) It must have superior impregnation characteristics.(5) Its vapor pressure must be low.The above characteristics of electrolyte greatlyinfluence the various characteristics of aluminumelectrolytic capacitors. For this reason, the properelectrolyte is determined by the electrical ratings,operating temperatures and the application of thecapacitor.NICHICON CORPORATIONTECHNICAL NOTES CAT.8101E-1
General Descriptions of Aluminum Electrolytic Capacitors1-5 Manufacturing Process of Aluminum Electrolytic CapacitorsProcessEtching(Enlargement of theSurface Area)Main MaterialsContentsHigh purity aluminum foilA 0.05 0.11 mm thick anode foil and a 0.02 0.05 mm thickcathode foil are continuously etched electrochemically in achloride solution with an AC or DC current. This enlarges theeffective surface area of the aluminum foils to attain smallercapacitor sizes.ChloridePure waterFormingEtched foil(Formation ofthe Dielectric)Borate, etc.SlittingThe process develops aluminum oxide (Al203) to form acapacitor dielectric.A high purity etched aluminum foil is anodized in a boric acidammonium water type solution, for example, to form analuminum oxide layer on the surface of the anode foil. As forthe cathode foil, an low DC voltage is sometimes used forformation, but there are also situations where formation is notconducted.Pure waterA foil is slited into specified widths according to capacitorcase sizes.Anode foilCathode foilSlited foils (anode/cathode)WindingElectrolytic paperLeadeAnode and cathode foils interleaved with an electrolytic paperare wound into a cylindrical capacitor element, with leadsbeing connected to both foils.Winding aftixing materialLeadWinding aftixingmaterialElementFoilElectrolyticpaperFig. 1 - 2TECHNICAL NOTES CAT.8101ENICHICON CORPORATION
General Descriptions of Aluminum Electrolytic n MaterialsContentsElementsElements are impregnated with liquid electrolyte.The clearance between the two electrode foils is filled withliquid electrolyte. With this impregnation, an element canfunction as a capacitor.ElectrolyteThe impregnated element, case and end seal are assembled.For the end seal , a rubber packing, a rubber lined bakeliteCase (usually aluminum)(with terminals) or a molded plastic plate (with terminals) areEnd sealused.Rubber packing,After assembly, the capacitors are covered with exteriorRubber-bakelite with terminals housing material. Sleeving is not used for laminate caseproducts, such as surface mount capacitors.Mold plastic with terminalsImpregnated elementsAssembly&Finishing()Exterior housing material(Sleeving, bottom plate, etc.)TerminalLead wireAluminum rivetCurled sectionAluminum lead tabRubber packingRubber-bakeliteCurled sectionAluminum washerAluminum lead tabElementSleevingAluminum caseAluminumcaseSleevingWinding affixing materialElement fixing material(may or may notbe - used)ElementBottom plateFig. 1 - 3Fig. 1 - 4laminate casing for laminate products (sleeveless)Assembled productsAgingDC voltage is applied under high temperature conditions toreform the oxide film.Plastic platformProcessingTaping materialAccessories(Capacitor mounting braket,terminal screws , etc.)Leads are processed and the plastic platform is attached tosurface mount capacitors.Depending on customer specification, the lead cutting,forming, snap - in and taping are processed.Accessories, such as mounting braket, are attached.Fig. 1 - 5An inspection based on the standard specification and testrequirements is performed to guarantee the quality ofproducts.InspectionPackagingPackaging materialsShippingTECHNICAL NOTES CAT.8101E-1NICHICON CORPORATION
General Descriptions of Aluminum Electrolytic Capacitors1-6 Characteristics1-6-1 CapacitanceThe capacitance of the dielectric portion of the anodealuminum foil can be calculated with the following formula(discussed in 1-1) :-- 8Ca 8.855 10εS（μF）dThe cathode foil has a capacitance (Cc) that uses theoxide layer, which formed by the forming voltage orformed naturally during storage (generally 1V or less), as adielectric. According to the construction of aluminumelectrolytic capacitors, Ca and Cc are connected in aseries. Therefore, the capacitance can be determined bythe following formula:C The impedance can be expressed by :1 jωL Rjω CZ Its absolute value can be expressed by :2Z R 2 （ωL ω1 ）CIts relation with frequencies is shown by a model curve.The inductance "L" is mainly from the wound electrodefoils and the leads.ESR "R" is from resistance of the electrode foils, theelectrolyte, the leads and each connection.Ca CcCa Cc10R (Ω), Z(Ω)The standard capacitance tolerance is 20%(M);however, capacitors with a capacitance tolerance of10%(K), etc. are also manufactured for special usage.The capacitance of aluminum electrolytic capacitorschanges with temperature and frequency of measurement,so the standard has been set to a frequency of 120Hz andotemperature of 20 C.110-1ZR10-21-6-2 Equivalent Series Resistance (R), DissipationFacter (tanδ), Impedance (Z)The equivalent circuit of an aluminum electrolyticcapacitor is shown below, The equivalent series resistanceis also known as "ESR".102103104105106Frequency (Hz)Fig. 1 - 8C Capacitance ( F )rRr Equivalent parallel resistance ofLanode oxide film (Ω)CR Equivalent series resistance (Ω)Fig. 1 - 6L Equivalent series inductance ( H )A reactance value due to the equivalent seriesinductance "L" is extremely small at low frequencies(50Hz 1kHz) and can be regarded as zero. Therefore,the following formula can be set up.ZR ω CRXctanδ DF tanδδXc10-3XLXcθRQ 1tanδ(ω 2πf)Fig. 1 - 7(1 - 3)100 (%)PF cosθ (1/ωc)(1 - 2)R ZXc RR2R 2(1 - 4)(ω1C)(1 - 5)1-6-3 Leakage CurrentThe causes of leakage current in aluminum electrolyticcapacitors are listed below :1)Distorted polarization of dielectric (aluminum oxidelayer)2)Resolution and formation of dielectric3)Moisture absorption by dielectric4)Breakdown of dielectric due to the existence ofchlorine or iron particles.The leakage current value can be decreased by properselection of materials and production methods; however,cannot be totally eliminated.Leakage current is also dependent upon time, appliedvoltage and temperature.The specified leakage current value is measured afterthe rated voltage of the capacitor is applied at roomtemperature for a specified time period. When selecting acapacitor for a particular application, characteristics suchas temperature dependency, aging stability and etc. mustbe taken into account.TECHNICAL NOTES CAT.8101ENICHICON CORPORATION
General Descriptions of Aluminum Electrolytic Capacitors1-6-4 Temperature CharacteristicsAluminum electrolytic capacitors have liquid electrolyte.This electrolyte has properties (conductivity, viscosity,etc.) that have rather conspicuous temperaturecharacteristics.Electrical conductivity increases as the temperatureincreases and reduces as the temperature decreases.Therefore, the electrical characteristics of aluminumelectrolytics are affected by temperature more than othertypes of capacitors. The following section explains therelationship between temperature and capacitance,tangent delta, ESR, impedance and leakage current.10-25oC1tan δ0.01100 20oCtan δ 65oC 105oC0.10.0110050V 1000µ F 105o C10k1kFrequency (Hz)Fig. 1 - 10 Tan δ vs. FrequencyCharacteristicsat 120HZ-10-2010-3050V 1000µF 105oC-402010-40-200204060Temperature (o C)80100120200V 470µ F 105 o Cat 120HZ0.01100-3010-40-40ESR Ω)-60Capacitance change (%)-25oC1-200204060Temperature (o C)80100120Fig. 1 - 9 Capacitance vs. Temperature Characteristics1k10kFrequency (Hz) 65oC 105oC100k200V 470µF 105oC-25oCESR(Ω)Impedance(Ω)Capacitance change (%)010k1kFrequency (Hz)10 200V 470µF 105oC2) Tanδ, Equivalent Series Resistance (ESR), ImpedanceThe Tan δ , equivalent series resistance (ESR) andimpedance changes with temperature and frequency. Anexample of the general characteristics is shown in Fig. 110 and 1-11.10 20oC 65oC 105oC0.11) CapacitanceThe capacitance of aluminum electrolytic capacitorsincreases as the temperature increases and decreases asthe temperature decreases. The relationship betweentemperature and capacitance is shown in Fig. 1-9.2050V 1000µF 105oC1ImpedanceESR0.1 20oC 65oC0.01100 105oC1k10kFrequency (Hz)100kFig. 1 - 11 Impedance, ESR vs. FrequencyCharacteristicsTECHNICAL NOTES CAT.8101ENICHICON CORPORATION
General Descriptions of Aluminum Electrolytic Capacitors3) Impedance RatiooThe ratio between the impedance at 20 C and theimpedance at various temperatures is called theimpedance ratio. Impedance ratio becomes smaller assmaller change of ESR and capacitance with temperature.The quality of performance at low temperatures isparticularly expressed with the impedance ratio at 120Hz.Leakage current (µA)10004) Leakage CurrentThe leakage current increases as the temperatureincreases and decreases as the temperature decreases.Fig. 1-12 shows the relationship between temperature andleakage current.50V 1000 µF 105oCMeasured after 1 minuteapplication of rated voltage100101-20Leakage current (µA)10000204060Temperature (oC)8010012080100120200V 470 µF 105oCMeasured after 5 minutesapplication of rated voltage100101-200204060Temperature (oC)Fig. 1 - 12 Leakage current vs. Temperature CharacteristicTECHNICAL NOTES CAT.8101ENICHICON CORPORATION
Application Guidelines for Aluminum Electrolytic Capacitors2. Application Guidelines for Aluminum Electrolytic Capacitors2-1 Application Guidelines2-1-1. Circuit Design( 1 ) Please make sure the application and mountingconditions to which the capacitor will be exposed arewithin the conditions specified in the catalog oralternate product specification (Referred as tospecification here after).( 2 ) Operating temperature and applied ripple currentshall be within the specification.qThe capacitor shall not be used in an ambienttemperature which exceeds the operatingtemperature specified in the specification.wDo not apply excessive current which exceeds theallowable ripple current.( 3 ) Appropriate capacitors which comply with the liferequirement of the products should be selected whendesigning the circuit.( 4 ) Aluminum electrolytic capacitors are polarized.Make sure that no reverse voltage or AC voltage isapplied to the capacitors. Please use bi-polarcapacitors for a circuit that can possibly see reversedpolarity.Note: Even bi-polar capacitors can not be used forAC voltage application.( 5 ) For a circuit that repeats rapid charging/dischargingof electricity, an appropriate capacitor that is capableof enduring such a condition must be used. Weldingmachines and photo flash are a few examples ofproducts that contain such a circuit. In addition,rapid charging/discharging may be repeated incontrol circuits for servomotors, In which the circuitvoltage fluctuates substantially.For appropriate choice of capacitors for circuit thatrepeat rapid charging/discharging, please consultNichicon.( 6 ) Make sure that no excess voltage (that is, higher thanthe rated voltage) is applied to the capacitor.qPlease pay attention so that the peak voltage, whichis DC voltage overlapped by ripple current, will notexceed the rated voltage.wIn the case where more than 2 aluminum electrolyticcapacitors are used in series, please make sure thatapplied voltage will be lower than rated voltage andthe voltage be will applied to each capacitor equallyusing a balancing resistor in parallel with thecapacitors.( 7 ) Aluminum electrolytic capacitors must be electricallyisolated as follows:The aluminum case and the cathode foil areconnected by the unstable resistance of a naturallyformed oxide layer inside the aluminum case and theelectrolyte.q(a) Case and negative terminal (except axial leadedpart such as JIS configuration 02 type)(b) Case and positive terminal(c) Case and circuit patternw(a) Auxialiary terminal of can type such as JIS stylesymbol 693, 694 or 695 and negative andpositive terminal, including the circuit pattern.eCase and both terminals of a bi-polarized capacitor.( 8 )qOuter sleeve of the capacitor is not guaranteed as anelectrical insulator. Do not use a standard sleeve on acapacitor in applications that require the electricalinsulation. When the application requires specialinsulation, please contact our sales office for details.wSecondary shrinkage, bulging and/or crack could beseen on outer sleeve of capacitor when capacitors areokept in more than 2 minutes at 150 C ambienttemperature during pre-heating at reflow process orresin curing process. Applying high temperature gas orheat ray to capacitor cause the same phenomenon.Further more, when temperature cycling test isperformed beyond JIS standard (Temperature Cycles),aforementioned sleeve problem could be seen. Thus,please confirm their adaptation before the use.( 9 ) Capacitors may fail if they are used under thefollowing conditions:qEnvironmental (climatic) conditions(a) Being exposed to water, high temperature & highhumidity atmosphere, or condensation of moisture.(b) Being exposed to oil or an atmosphere that isfilled with particles of oil.(c) Being exposed to salty water or an atmospherethat is filled with particles of salt.(d) In an atmosphere filled whith toxic gasses (such ashydrogen sulfide, sulfurous acid, nitrous acid,chlorine, bromine, methyl bromide, ammonia, etc.)(e) Being exposed to direct sunlight, ozone,ultraviolet ray, or radication(f) Being exposed to acidic or alkaline solutionswUnder severe conditions where vibration and/ormechanical shock exceed the applicable ranges ofthe specifications.(10) When designing a P.
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