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Technical Note Judicious Use of Aluminum Electrolytic Capacitors Contents 1. Overview of Aluminum Electrolytic Capacitors 1 － 1 Basic Model of Aluminum Electrolytic Capacitors 1 － 2 Structure of Aluminum Electrolytic Capacitors 1 － 3 Features of Capacitor Materials 1 － 4 Manufacturing process 2. Basic Performance 2 － 1 Basic Electrical Characteristics 2 － 2 Frequency Characteristics of Impedance 3. Reliability 4. Failure Modes 5. Lifetime of Aluminum Electrolytic Capacitors 5 － 1 Ambient Temperature Effect on Lifetime 5 － 2 Applying Voltage Effect on Lifetime 5 － 3 Ripple Current Effect on Lifetime 5 － 4 Charge and Discharge Operation Effect on Lifetime 5 － 5 Inrush Current 5 － 6 Abnormal Voltage Effect on Lifetime 6. Effect of Halogens 6 － 1 Effect of Flux 6 － 2 Cleaning Agents 6 － 3 Adhesive and Coating Materials 6 － 4 Effect of Fumigation 7. Recovery Voltage 8. Storage 9. Tips for Selecting Capacitors Appropriate for Individual Applications 9 － 1 Input Filtering Capacitors for Switching Mode Power Supplies 9 － 2 Output Filtering Capacitors for Switching Mode Power Supplies 9 － 3 Filtering Capacitors for Inverter Main Circuits 9 － 4 Capacitors for Control Circuits 9 － 5 Photoflash Capacitors TECHNICAL NOTE 1．Overview of Aluminum Electrolytic Capacitors d Dielectric 1-1 Basic Model of Aluminum Electrolytic Capacitors Capacitors are passive components. Among the various kinds S of capacitors, aluminum electrolytic capacitors offer larger CV product per case size and lower cost than the others. εr In principles of capacitor, its fundamental model is shown in Fig. 1 and its capacitance (C) is expressed by Equation (1) below: εrS C ＝ 8.854×10 － 12 （F） …………………………………（1） Fig-1 Basic model of capacitor d εr ： Dielectric constant Dielectric（Al2O3） Ｓ ： Surface area of dielectric（m2） ｄ ： Thickness of dielectric（m） Equation (1) shows that the capacitance (C) increases as the dielectric constant (εr) and/or its surface area (S) increases and/or Separator the dielectric thickness (d) decreases. Anode foil Cathode foil An aluminum electrolytic capacitor comprises a dielectric layer of aluminum oxide (Al2O3), the dielectric constant (εr) of which is 8 to 10. This value is not significantly larger than those of other types of Electrolyte capacitors. However, by extending the surface area (S) of the aluminum foil DA DC electrode by means of etching, and by electrochemically forming a LA LC R thinner but highly voltage-withstandable layer of oxide layer dielec- CA CC tric, the aluminum electrolytic capacitor can offer a larger CV prod- uct per case size than other types of capacitors. RA RC A basic model of aluminum electrolytic capacitor is shown in Fig. 2. An aluminum electrolytic capacitor comprises: CA、CC：Capacitance due to anode and cathodes foils DA、DC：Diode effects due to oxide layer on anode and cathode foils Anode …Aluminum foil LA、LC ：Inductance due to anode and cathode terminals Dielectric…Electrochemically formed oxide layer (Al O ) on 2 3 R ：Resistance of electrolyte and separator the anode R 、R ：Internal resistance of oxide layer on anode and cathode foils Cathode …A true cathode is electrolytic solution (electrolyte). A C Other component materials include a paper separator that Fig-2 Basic model and equivalent circuit of aluminum holds electrolyte in place and another aluminum foil that func- electrolytic capacitor tions as a draw-out electrode coming into contact with the true cathode (electrolyte). In general, an aluminum electrolytic capacitor is asymmetrical Lead Wire (Terminal) in structure and polarized. The other capacitor type known as a Aluminum Tab bi-polar (non-polar) comprises the anodic aluminum foils for Separator Paper both electrodes. Cathode Foil Anode Foil 1-2 Structure of Aluminum Electrolytic Capacitor The aluminum electrolytic capacitor has, as shown in Fig. 3, a roll of anode foil, paper separator, cathode foil and electrode terminals (internal and external terminals) with the electrolyte impregnated, which is sealed in an aluminum can case with a sealing material. Fig-3 Basic model of element The terminal draw-out structure, sealing material and structure differ depending on the type of the capacitor. Figure 4 shows typical examples. Vent Element Can Sleeve Can Coated Can Sleeve Rubber Seal Element Element Aluminum Tab Lead Wire Rubber Seal （Terminal） Aluminum Tab Aluminum Tab Terminal Plate Sealing Material Lead Wire（Terminal） （Surface Mount Type） Terminal （Radial Lead Type） （Snap-in Type） Fig-4 Construction of Aluminum Electrolytic Capacitors Product specifications in this catalog are subject to change without notice.Request our product specifications before purchase and/or use. Please use our products based on the information contained in this catalog and product specifications. CAT. No. E1001V 2021 TECHNICAL NOTE 1-3 Features of Capacitor Materials 1-4 Manufacturing Process Aluminum, which is main material in an aluminum electrolytic ① Etching (for extending the surface area) capacitor, forms an oxide layer (Al O ) on its surface when the 2 3 This etching process serves to aluminum is set as anode and charged with electricity in elec- extend the surface area of the trolyte. Aluminum base aluminum foil. This is an AC or material The aluminum foil with an oxide layer formed thereon, as DCcurrent-employed electrochem- shown in Fig. 5, is capable of rectifying electriccurrent in elec- Etching Model ical process for etching the foil trolyte. Such a metal is called a valve metal. surface in a chloride solution. Al2O3 I ② Formation (for forming a dielectric) This is a process for forming a dielectric layer (Al O ), which is V 2 3 0 normally performed on the anode aluminum foil. Forming Model ③ Slitting Blade Fig-5 V-I characteristics of aluminum oxide This is a process for slitting alumi- num foils (both the anode and <Anode aluminum foil> cathode) and paper separators to First, the foil material is electromechanically etched in a chloride the specified product size. Slitting Model solution to extend the surface area of the foil. Secondly, for the foil to form an aluminum oxide layer (Al2O3) as a Lead Wire ④ Winding (Terminal) Anode Foil dielectric, more than the rated voltage is applied to the foil in a solu- Separator Paper tion such as ammonium borate. This dielectric layer is as dense and This is a process for rolling a set of thin as 1.1 - 1.5 nm/volt and showing a high insulation resistance anode and cathode foils into a cylin- (108 - 109 Ω/m). drical form with a paper separator The thickness of the oxide layer determines the withstand voltage inserted between them. During this Cathode Foil according to their direct proportional relationship. For the etching process, an inner terminal (called a tab) is attached to each of the alumi- pits to be shaped to the intended thickness of the oxide layer, the pit Electrolyte patterns have been designed to have efficient surface area exten- num foils. The roll made at this sion depending on the intended withstand voltage (see Fig. 6) process is called a capacitor element. <Cathode aluminum foil> ⑤ Impregnation An etching process is performed to the cathode aluminum foil as This is a process for impregnating well as the anode foil. However, the formation process for oxide the element with electrolyte as a Impregnation layer is generally not performed. Therefore, the surface of the true cathode. The electrolyte also cathode foil only has an oxide layer (Al2O3) that has spontane- functions to repair the dielectric ously formed, which gives a withstand voltage of about 0.5 volt. layer. Low Voltage Foil High Voltage Foil ⑥ Sealing Aluminum Can This process seals the element using the aluminum can case and sealing materials (rubber,rubber- lined cover, etc.) for keeping the Element case airtight. ⑦ Aging (reforming) （Fracture surface of AC etched foil） （Fracture surface of DC etched foil） Replica The process of applying voltage to a post-sealed capacitor at high tem- Fig-6 Cross section of aluminum etched foil SEM) Rubber （ perature is called “aging”. This serves to repair defective dielectrics <Electrolyte> that have been made on the foil The electrolyte, an ion-conductive liquid functions as a true during the slitting or winding process. cathode coming into contact with the dielectric layer on the sur- face of the anode foil. The cathode foil serves as a collector ⑧ 100% inspection and packaging electrode to connect the true cathode with the external circuit. Electrolyte is an essential material that controls the perfor- After the aging, all products shall mance of the capacitor (temperature characteristics, frequency undergo testing for checking their characteristics, service life, etc.). electrical characteristics with chip termination, lead reforming, taping <Paper separator > etc. finished, and then be packaged. The separator maintains uniform distribution of the electrolyte and keeps the anode-to-cathode foil distance unchanged. ⑨ Outgoing inspections Outgoing inspections are per- <Can case and sealing materials> formed as per standard inspection An aluminum can case and seal materials mainly consisting of procedures. rubber are used for the purpose of keeping airtightness. ⑩ Shipment Product specifications in this catalog are subject to change without notice.Request our product specifications before purchase and/or use. Please use our products based on the information contained in this catalog and product specifications. CAT. No. E1001V 2021 TECHNICAL NOTE Ex. 35V470µF Radial Lead Type at 105℃ ２．Basic Performance 20 15 10 5 2-1 Basic Electrical Characteristics 0 -5 2-1-1 Capacitance -10 -15 The larger the surface area of an electrode is, the higher the -20 -25 capacitance (capacity for storing electricity) is. For aluminum Capacitance Change (%) -30 -35 electrolytic capacitors, the capacitance is measured under the -40 -60 -40 -20 0 20 40 60 80 100 120 standard measuring conditions of 20°C and a 120Hz AC signal Temperature(℃) of about 0.5V. Generally, as the temperature rises, the capaci- Fig-7 Temperature Characteristics of Capacitance tance increases; as the temperature decreases, the capaci- tance decreases (Fig.
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